PART I
GUIDANCE FOR THE LOCATION STANDARDS
Chapter 2
Locating Hazardous Waste Facilities in Seisoically Active Areas
This Section Prepared By:
Woodward-Clyde Consultants
3 Embarcadero Center, Suite 700
San Francisco, California 94111
and
Cynthia Hoppmann
Offica of Solid Waste
U.S. Environmental Protection Agency
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TABLE OF CONTENTS
LIST OF ILLUSTRATIONS 2-5
LIST OF TABLES 2-5
1.0 INTRODUCTION 2-7
2.0 REGULATOR! BACKGROUND 2-9
2.1 The Seismic Location Standard 2-9
2.2 Summary of Technical Rationale 2-14
3.0 DEFINITIONS 2-15
4.0 DEMONSTRATING COMPLIANCE WITH THE SEISMIC LOCATION 2-21
STANDARD
4.1 Methods and Tools of Geologic Investigations 2-24
4.1.1 Review of Existing Data 2-24
4.1.2 Analysis of Aerial Photographs 2-27
4.1.3 Aerial Reconnaissance 2-30
4.1.4 Ground Geologic Reconnaissance 2-31
4.1.5 Subsurface Exploration 2-32
4.2. Information in Part B of the RCRA Permit 2-36
5.0 REFERENCES 2-39
APPENDIX A: GENERAL DISCUSSION OF EARTHQUAKES AND FAULTING 2-43
APPENDIX B: FAULTING AND GE0M0RPHIC FEATURES OF FAULT 2-52
ZONES
APPENDIX C: HOLOCENE DEPOSITS AND ACTIVE FAULTING 2-63
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LIST OF ILLUSTRATIONS
Figure Number
1
2
3
4
Table Number
1
2
Areas of Che United States Listed In 2-13
Appendix VI
Types of Surface Faulting 2-20
Log of an Exploratory Excavation 2-35
Across the Active Eayward Fault
Three Types of Fault Displacement 2-58
LIST OF TABLES
Page
Political Jurisdictions In Which 2-11
Compliance with 5264.18(a) oust be
Demonstrated (Appendix VI to Part 264)
Public Inquiries Offices of the U.S. 2-26
Geological Survey
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1.0 INTRODUCTION
This chapter of the Guidance Manual for the Location Standards
provides guidance to EPA permit writers and owners or operators of
new hazardous waste management facilities concerning the seismic
location standard in 40 CFR 264.18(a) and the corresponding Part B
(RCSA permit) information requirements in 40 CFR 122.25(a)(11).
Beyond this introduction, the second section of this chapter
describes the seismic location standard and provides a summary of the
technical basis for the standard. Section 3.0 defines geological
terms used in the standard and this Manual. Section 4.0 provides a
detailed discussion of the Part 122 information requirements and the
methods and tools of geologic investigations. The references are in
Section 5.0. . Three appendices follow, providing background
information on earthquakes, faulting, and Holocene deposits.
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2.0 REGULATORY BACKGROUND
2.1 The Seismic Location Standard
The potential threat that a hazardous waste management facility
presents to human health and the environment is increased by locating
the facility in seismically active areas. Damage and loss of life in
earthquakes occur as a result of ground shaking (ground motion),
secondary effects of the shaking such as liquefaction, and permanent
surface displacement along faults (surface faulting). The siesmie
location standard addresses one of these hazards, surface fault
displacement, and the associated ground deformation in the vicinity
of the displacement. Specifically, the seismic location standard
prohibits hazardous waste management facilities from locating within
61 meters (200 feet) of a fault that has had displacement in Holocene
time (approximately the last 11,000 years)* Such a fault is referred
to as a "Holocene fault" within this document.
Surface fault displacement and deformation do not represent a
significant risk to hazardous waste facilities in the entire United
States. Even though large earthquakes have occurred in the East*,
a surface fault has not been conclusively identified as being
associated vith these earthquakes. Because displacement cc
deformation along Holocene faults, the very processes that the
*As used in this manual, "in the East" means east of the eastern
front of the Rocky Mountains.
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seismic standard is intended to protect against, do not present a
significant risk to hazardous waste facilities in the East, the
seismic location standard Impacts only those new facilities that are
proposed to be located In certain areas vest of the eastern front of
the Rocky Mountains. Appendix VI to P. ~t 264 lists those political
jurisdictions where ZPA has determined that applicants must
demonstrate compliance with the seismic location standard.
For reasons specified In the ___________Federal Register
( FB. ) EPA amended the January 12th version of Appendix VI. The
preceding discussion is consistent with that amendment. The amended
version of Appendix VI is given in Table 1 and mapped in Figure 1.
Sections 122..25(a) (11) (i) and (il) of Part 122 contain the
information requirements for Part B of "he RCRA permit application
relative to the seismic location standard (see 46 FR 2889). Part 122
requires permit applicants whose facilities ace located in areas
listed is Appendix VI to demonstrate either that Holocsne faults are
not present within a 3,000-foot radius of the facility or that
Bolocene faults are not present within 200 feet of the facility.
However, if Holocene faults are determined to be present within a
3,000-foot radius of the facility, the applicant must also
demonstrate that Holocene faults are not present within.200 feet of
the facility. Part 122 also specifies investigative methods that may
be used to-make the above described demonstrations.
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TABLE 1
POLITICAL JURISDICTIONS* IN WHICH COMPLIANCE WITH
5264.18(A) MOST BE DEMONSTRATED (APPENDIX VI TO PART 264)
Alaska
Colorado (Concluded)
Aleutian Islands
Anchorage
Bethel
Bristol Bay
Cordova-Valdez
Fairbanks-Fort Yukon
Juneau.
Keaai-Cook. Inlet
Ketchikan-Priace of Wales
Kodlak
Lynn Canal-Icy Straits
Palaer-Wasilla-Talkeena
Seward
Sitka
Wade Hampton •
Wrangell-Petersburg
Yukon-Kuskokwlm
Arizona
Cochise
l^pliam
Greenlee
Yuma
Mineral
Rio Grande
Saguache
Hawaii
Hawaii
Idaho
Bannock
Bear Lake
Bingham
Bonneville
Caribou
Cassia
Clark
Franklin
Fremont
Jefferson
Madison
Oneida
Power
Teton
California
All
Colorado
Archuleta
Conejos
Hinsdale
Montana
Beaverhead
Broadwater
Cascade
Deer Lodge
Flathead
Gallatin
Granite
*These include counties, city-county consolidations, and indepen-
dent cities. In Che case of Alaska, the political jurisdictions
are election districts, and, In the case of Hawaii, the political
jurisdiction listed is the island of Hawaii.
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TABLE 1 (Concluded)
Montana (Concluded)
Jefferson
Lake
Lewis and Clark
Madison.
Meagher
Missoula
Park
Powell
Sanders
Silver Bow
Stillwater
Sweet Grass
Teeon
Wheatland
Nevada
All
New Mexico
Bernalillo
Catron
Grant
Hidalgo
Los Alamos
Bio Arriba
Sandoval
Santa Fe
Sierra
Socorro
Xaos
Torrance
Valencia
Ptah
Bearer
Box Elder
Cache
Carbon
Davis
Duchesne
Emery
Garfield
Ir^n
m
U
Utah (Concluded)
Juab
Millard
Morgan
Piute
Rich
Salt Lake
Sanpete
Sevier
Summit
Tooele
Utah
Wasatch
Washington
Wayne
Weber
Washington
Chelan
Clallam
Clark
Cowlitz
Douglas
Ferry
Grant
Grays'Harbor
Jefferson
King
Kitsap
Kittitas
Lewis
Mason
Okanogan
Pacific
Pierce-
San Juan Islands
Skagit
Skamania
Snohomish
Thurston
Wahkiakum.
Whatcom
Yakiaa'
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FIGURE 1
AREAS OF THE UNITED STATES LISTED
IN APPENDIX VI
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As Indicated In the preamble to the January 12 rules, EPA did
not promulgate location standards addressing ground motion and ground
failure because the Agency lacked sufficient data and information
relating ground motion and ground failure risks to hazardous waste
facility siting and design. These issues are discussed in greater
depth on page ZS11 of the January 12th Federal Register (Vol. 46, Ho.
7) (U.S. Environmental Protection. Agency, 1981).
2.2 Stannary of Technical Rationale*
It is generally considered economically infeasible and, in some
2
eases, Impossible to design a critical structure to resist
significant fault displacement. Tor this reason many regulatory
agencies prohibit the construction of certain structures adjacent to
faults that have the potential for surface faulting during the life
of the structures (SIamnions, 1977) ..
SPA prepares Background Documents which contain technical support
for regulations promulgated under the authority of RCRA. The
Background Document General Facility Standards for Location of
Facilities (December 30, 1980; MS. 1941. 34) should be read for an
in-depth discussion of the Agency's technical rationale with
respect to the seismic location standard.
"Examples of critical structures are dams, reservoirs, nuclear
reactors, tall building, schools, prisons, and structures
containing large quantities of potentially explosive or toxic
materials (California Seismic Safety Committee, 1979).
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Hazardous waste management facilities encompass treatment,
storage or disposal of hazardous waste in containers, tanks, surface
impoundments, vaste piles, landfills, incinerators, and structures or
mediums for thermal, chemical, physical, and biological-treatment.
These facilities contain structures similar to those that have been
damaged during past historical earthquakes and episodes of surface
faulting (U.S. Geological Survey, 1971; Murphy, 1973; and Earthquake
Engineering Research Institute, 1979). Therefore, in order to
protect human health and the environment, there is a need to regulate
the location of hazardous waste management facilities in areas
subject to fault displacement*
The basic premise applied to Identifying and locating faults
that may be significant to man-made structures is that the type,
amount, and location of fault displacement In the future will be
similar to that which has occurred in the recent geologic past. This
premise has been substantiated by the results of studies that
demonstrate that surface fault rupture typically is confined to a
relatively narrow zone along a pre-existing fault trace (Cluff, 1968;
Rogers, 1973; Slemmons, 1969; Swan, Schwartz, and Cluff, 1980; and
Vallace, 1968).
The evaluation of a given site with regard to the potential
hazard of surface fault rupture is based extensively on the concepts
of recency and recurrence of faulting along existing faults. In a
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general way, the sore recent the faulting, the greater the
probability for future faulting (Ziony, Wentworth, and Buchanan,
1973). In other words, faults that have had displacnent in Holocene
time are more likely to displace in the near future than faults whose
last displacement occurred during the Eocene (58 to 36 million years
before the present) and earlier.
In almost all known Instances of historical faulting, surface
displacements have occurred along a pre-existing fault that had
previous displacement in Eolocene time and could have been recognized
by geologists prior to the faulting as a potential source of future
activity (Cluff, Slemmons, and Waggoner, 1970). The geologie and
historic record of fanlt activity shows that is is very likely that
the displacement along a given fault will occur on or near the most
recently active fault trace (Sherard, Cluff, and Allen, 1974;
Wallace, 1968). For an engineering project or structure located
across or in the vicinity of a fault,, the primary consideration is
the potential for recurrent movement on that fault within a time
period that is significant to that project, or structure. ZPA has
determined that faults that have had displacement during Holocene
time are likely to experience recurrent movement at a frequency that
is significant to hazardous waste facilities.
Non-compliance with the seismic location standard could result
in the placement of a facility across a Holocene fault. These faults
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have a high probability of displacement within the life of the
facility, and therefore, such displacement could result in loss of
life, damage to the environment, or both.
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3.0 DEFINITIONS
Branch fault - A fault or fault trace that diverges from a main fault
(see Figure 2).
Displacement* - The relative movement of any two sides of a fault
measured in any direction.
Fault* - A fracture along which rocks on one side have been displaced
with respect to those on the other side.
Fault trace - The line formed by the intersection of a fault and the
ground surface or near-surface materials. The representation of a
fault as depicted on a map.
Fault zone - A zone of related faults, which are commonly braided and
parallel but may be branching and divergent.
Holocene* - The most recent epoch of the Quaternary period, extending
from the end of the Pleistocene to the present. A geological
epoch that represents about the last 11,000 years. In some parts
of the United States the upper limits of the Holocene may range
from 10,000 to 15,000 years ago. This definition also includes
recent historic time of about the last ZOO years.
Main fault - The fault with the greatest displacement, length, and
continuity. Sometimes referred to as first, original, primary, or
principal fault trace (see Figure 2)•
Secondary fault - A fault that is completely separate spatially from
the main fault. The displacement is generally of the same type as
the main fault, but the amount of displacement is less (see Figure
2).
Surface faulting - Displacement or deformation at or near the ground
surface caused by movement along a fault.
*These terms are also defined in the seismic location standard in
Section 264.18(a).
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I
III
/
III
II
No Sal*
SOURCE: SonilU. 1967
I - Main
II - Branch
III - Secondary
FIGURE 2
TYPES OF SURFACE FAULTING.
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4.0 DEMONSTRATING COMPLIANCE WITH THE SEISMIC LOCATION STANDARD
Compliance with the seismic location standard may be
demonstrated using either published geologic data or data obtained
from field investigations carried out by the permit applicant. The
information submitted to EPA oust demonstrate either that Holocene
faults are not present within a 3,000-foot radius of the facility or
that Holocene faults are not present within 200 feet of the
facility. However, if Holocene faults are determined to be present
within a 3,000-foot radius of the facility, the applicant must also
demonstrate that Holocene faults are not present within 200 feet of
the facility.
Part 122 [40 CFR 122.25(a)(11)] specifies that the 3,000-foot
demonstration must be based on information obtained from published
geologic studies, aerial reconnaissance within a five-mile radius of
the facility, analysis of aerial photographs for an area within a
3,000-foot radius of the facility, and if necessary to make the
demonstration, a reconnaissance based on walking portions of the area
within 3,000 feet of the facility. The 200-foot demonstration must
be based on data from a comprehensive geologic analysis of the site
and, if necessary to make the demonstration, a subsurface exploration
(See 46 FR 2889).
General guidance can be given as to when it would be more
efficient to conduct a 200-foot study rather than a 3,000-foot
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study• la the following instances It is generally advisable to do a
200-foot study:
(1) If reliable data Indicate that active faults are located
near the site
(2) If the age of surface materials at the site demonstrates
that the site (and the area within a 200-foot radius of
those portions of the facility where hazardous waste will
be treated, stored, or disposed of) Is underlain by
unfanlted materials older than Eolocene age.
Because EPA's intent In the Part 122 language Is not always
clear, the Agency hopes that the bulleted information produced here
will help in that regard.
• The sequential listing of investigative methods in Section
' 122.25(a)(11)(1)(A) is not meant to imply that the permit
applicant must obtain data using each method listed. Rather,
only those Investigative methods that will provide needed
information should be used. The Agency certainly does not
want the applicant to repeat geological studies that have
already been performed in the area. To this end, It is
always advisable to review and analyze all geological
information that Is available for the area before proceeding
to conduct new geologic studies.
» If an aerial reconnaissance or analysis of aerial
photographs will not yield pertinent Information because the
geology of an area is obscured by development or forestatlon,
then such areas should not be studied using those methods.
• The last sentence under Section 122.25(a) (H)(1)(B), "Such
investigation shall document with supporting maps and other
analysis, the location of any faults found," is also meant to
apply to investigations carried out under
122.25(a) (H)(1)(A).
» In Section 122.25(a)(ll)(i)(B)v the 200-foot study is based
on data from a "comprehensive geologic analysis of the
site**. EPA intended for this comprehensive geologic analysis
to include, at a minimum, a review of available geological
information for a distance of 3,000 feet from the facility
and'a ground geological reconnaissance for the same
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distance. If this information or any additional information
that the applicant provides is not sufficient to conclude
that it is extremely unlikely that Holocene faults exist
within 200 feet of the facility, some type of subsurface
exploration will have to be conducted.
Because of the potential complexity of the required
demonstration, Regional Offices that are responsible for political
jurisdictions listed in Appendix 71 to Part 264 and owners and
operators of new facilities that are proposed to be located in these
jurisdictions should consider seeking the help of a geologic
consultant experienced in identifying and evaluating fault activity.
In summary, Part 3 of the RCRA permit application should contain
documentation, by a qualified geologist, that portions of the
facility where treatment, storage, or disposal of hazardous waste
will be conducted will not be located within 200 feet of a Holocene
fault. The documentation should be appropriate for the site and the
tectonic environment and should be of such quality as to be
acceptable to geologists experienced In identifying and evaluating
fault activity.
The remainder of this section contains a discussion of the
methods and tools for conducting geological investigations and the
information that should be included in Part B of the RCRA permit
application.
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4.1 Methods and Tools ef Geologic Investigations
The methods aad tools for conducting both the 3,000-foot and
200->£oot geologic investigations include a review of published data,
aerial reconnaissance, interpretation of aerial photographs, ground
reconnaissance, and subsurface investigations. These tools are used
to id en faults and llneatlons (linear features that suggest the
presence of a fault) that nay be associated with 3olocene fault
displacement and to determine if such faults have had displacement In
Holocene time.
4,1.1. Review of Existing Data
The review of existing data Is directed toward obtaining
geologic and seismic information about the areas surrounding the
facility. Any available Information on the area's geology, degree
and reer -jcy of fault activity, and earthquakes for which recorded
information exists should be reviewed to determine if any Holocene
faults have been identified and to further identify any structural
trends that may be related to faulting. Also, concentrations of
earthquake activity, and historical accounts of major earthquakes and
surface effects in the project area, may Indicate the presence and
location of faults.
Published Information on the location of faults near the site
and the recency of their activity may exist. Because fault-related
studies of a particular site will not exist in many cases, geological
Information will usually have to be reviewed for a larger area.
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The purpose of reviewing existing data is to determine what Is
currently known about the geology of the area surrounding the
facility. After this knowledge has been gained, one can determine if
some type of field investigation (e.g., aerial reconnaissance, ground
reconnaissance, borings) must be conducted to demonstrate compliance
with the seismic location standard.
Before new field studies are conducted, it is advisable for the
permit applicant to inform the appropriate permitting official of his
plans for the study. Potential problems may surface at this stage
and can be worked out before time and money are spent on field
studies that may be inadequate.
The United States Geological Survey (USGS) and the geological
surveys of the Individual states are good sources of information
concerning geology, faults, and historic earthquakes. The USGS
operates nine Public Inquiries Offices, listed In Table 2, to provide
Federal and state agencies and the general public with convenient
access to Information about Survey activities and products.
Over-the-counter and mall order sales Include topographic, geologic,
and hydrologic maps and book reports relating to the geographic area
of each office. Offices provide question-answering, interpretive,
and referral services. Other sources Include local offices of the
Soil Conservation Service of the U.S. Department of Agriculture,
local colleges and universities, county and city building departments
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TABLE 2
PUBLIC INQUIRIES OFFICES OF THE
U.S. GEOLOGICAL SURVEY
108 Skyline Building
508 Second Avenue
Anchorage, Alaska 99501
(907) 277-0577
FTS 399-0150 (Seattle number -
ask for Anchorage number)
7638 Federal Building
300 North Los Angeles Street
Los' Angeles, California 90012
(213) 688-2850
FTS 798-2850
1045 Federal Building
1100 Comerce Screet
Dallas, Texas 75202
(214) 749-3230
FTS 749-3230
8102 Federal Building
125 South Seate Street
Salt Lake City, Utah 84138
(801) 524-5652
FTS 749-5652
504 Customhouse
555 Battery Street
San Francisco, California 94111
(415) 556-5627
FTS 556-5627
302 National Center
Room 16402
12201 Sunrise Valley Drive
Reston, Virginia 22092
(703) 860-6167
FTS 928-6167
1012 Federal Building
1961 Stout Street
Denver, Colorado 80202
(303) 837-4169
FTS 327-4169
1028 General Services
Administration Building
19th and F Streets, N.W.
Washington, D.C. 20244
(202} 343-8073
FTS 343-8073
67? U.S. Courthouse
West 920 Riverside Avenue
Spokane, Washington 99201
(509) 456-2524
FTS 439-2524
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or public works departments, and consulting geologists. The
references used during the study and the sources of data should be
cited in Part B of the RCRA permit application to support information
obtained that demonstrates compliance with the seismic location
standard.
4.1.2 Analysis of Aerial Photographs
Studies of aerial photographs and other remote-sensing images
are an essential part of fault investigations. However, aerial
photographs may be of limited use In forested areas or in areas that
were developed before the photographs were taken. In many cases,
features of faults can be observed on aerial photographs that could
not be readily Identified during land-based studies. The traces of
some faults can be easily and immediately Identified. At the other
extreme, the.surface features of some faults seen on the aerial
photographs may be so small and relatively Insignificant that they
can only be recognized as suspicious features by a geologist with
considerable experience in studying faults -and In aerial phtographlc
interpretation. There is a. large element of experience and judgment
in the interpretation of aerial photographs, particularly in the
interpretation of Holocene fault activity.
Until the past few years, ordinary black-and-white photographs
have been used for aerial photography. Much o£ the world has been
photographed at scales of 1:30,000 to 1:60,000. These photographs
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are especially good for preliminary regional investigations and
should be obtained if possible, because a large area is covered by
few photographs. For more detailed studies, scales of 1:12,000 to
1:20,000 are preferable. For stereoscopic viewing, which is
absolutely necessary, 60 percent overlap and 30 percent sidelap ar
standard' practice. The ability to interpret the photographs is
somewhat dependent on the quality of the photography, but it is, t a
larger degree, dependent on the quality of the printing.
Aerial photographs not taken specifically for fault studies s
usually taken during midday. Starting in 1967, a research prograr
was carried out jointly by the University of Nevada Department of
Geology-Geography and Woodward-Lundgren & Associates; In this prog us
new photographic techniques were developed for the specific puzpos
of studying active faults. A recent procedure of low-sun-engle
aerial photography utilizes photographs taken at different times c
the day, and sometimes in different seasons of the year, depending m
the fault trend and the azimuth of the sunlight (Cloff. and Brograc
1974). The purpose of the photography is to enhance shadows from
subdued ground-surface irregularities. The optimum light condltic
Is obtained when the sun is shining nearly perpendicular to the tx id
of the fault, in the direction from the uphill side of the fault
scarp toward the downhill side, at an angle slightly lower than tfc
average slope of the scarp (usually 10® to 25°). The most
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universally useful scale Is about 1:12,000, with scales of 1:6,000
and 1:3,000 good for detailed analyses. While it is desirable to
repeat the photography in both the early morning and late afternoon,
experience has shown that photographs taken either in the early
morning or late afternoon pick up most of the detail that can be
obtained by flying at both times (Cluff and Brogan, 1974). Other
types of images that are helpful include infrared and color images,
photographs from satellites, and high-altitude aircraft photographs.
In summary, the following points may be made:
• The most useful type of photograph is the black-and-white,
low-sun-angle, vertical aerial photograph.
• When photographs are taken for the purpose of a fault study,
color photographs are superior to black-and-white photographs
taken at midday, but not to low-sun-angle black-and-white
aerial photographs.
•> The infrared photograph occasionally gives a better
indication of differences in ground-water level or vegetation
contrasts on the opposite sides of a fault, but low-sun-angle
photographs appear to be better for evaluating fault
activity.
» Satellite and high-altitude aircraft images can be useful
for Identifying structures that need careful evaluation using
low-sun-angle photography or field studies.
Documentation of analysis of aerial photographs should include
sources of photographs, photograph numbers, data photographs were
taken, type of photographs, and either copies of photographs or
plastic overlays on which analysis Is made. Aerial photographs can
generally be obtained from local aerial photographic companies, the
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Agricultural Stabilization and Conservation Service, Soil
Conservation Service, or U.S. Geological Survey.
4.1.3 Aerial Reconnaissance
Aerial reconnaissance can be used to identify geomorphic fault
features that are not readily identifiable on the ground. Of course,
use of this method is United by the degree that the subject area is
forested or developed. Faults may appear visually as lineations or
linear alignments of features resulting from various physical
conditions created by faulting, such as disruption of the normal
ground surface along the traces of previous fault breaks; different
soils, rock types, and vegetation on opposite sides of the fault; and
displaced topographic features. These features Include scarps,
offset drainage channels, saddles-, sag pondsr ponded alluvium, closed
depressions, and shutter ridges or parallel ridges» The gecmorphic
features of fault zones are discussed is Appendix B of this document
and are wall described by Slemons (1977) .
Aerial reconnaissance is best done in a high-winged aircraft
when the visibility is good. Early morning or late afternoon flights
are generally better than midday flights because shadows enhance
subdued ground-surface irregularities Along fault zones. The flight
lines should consist of two different orientations: one
perpendicular to the geologic structures and the other one parallel
to the geologic structures. In most cases it is best to have two
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observers, one oil each side of the aircraft, in order to take
advantage of the difference in lighting conditions. The observers
should have previous experience in identifying fault-related features
from aircraft. Documentation of aerial reconnaissance should include
the name of the flying service, the date of the flight, the type of
aircraft, observations outlined on a topographic nap, and 35nm slides
of flight observations.
4.1.4 Ground Geologic Reconnaissance
A ground geologic reconnaissance is made to observe geological
and geomorphic features that nay be associated with faults,
especially Holocene faults. If a fault has been active recently,
geooorphic evidence will be expressed at a few locations along its
length. Therefore, more confidence in conclusions drawn from a
ground reconnaissance can be obtained by extending the reconnaissance
beyond the site (i.e., out to 3,000 feet fron the facility),
examining locations of known faults in the area for type of faulting
and evidence of activity, examining lineatlons or suspicious features
identified during the aerial reconnaissance or on aerial photographs,
and describing any stratlgraphic evidence that would demonstrate a
lack of Holocene fault activity in the vicinity of the site. Ground
reconnaissance should be documented by showing observations on a
topographic map or photo overlay and by providing 35mm slides of
observations and an original geologic map.
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4.1.5 Subsurface Exploration
The purpose o£ subsurface exploration is to demonstrate (1) the
presence or absence of faults within 200 feet of portions of the
facility where treatment, storage, or disposal of hazardous waste
will be conducted and (2) to determine whether any of these faults
have had displacement in Holocene time or at some older time period.
Subsurface exploration may consist of:
» Trenching and other extensive excavations to permit detailed
and direct subsurface observations
» Borings and test pits to permit collection of data at
specific locations and depths
•- geophysical Investigations of subsurface conditions
Geophysical methods are indirect methods to measure variations
and* anomalies in subsurface strata. These variations and anomalies
may or may not be faults. Therefore, they require specific knowledge
of subsurface conditions for reliable interpretation. Geophysical
methods alone do not prove the absence of a fault nor the recency of
fault activity.
The purpose of a geophysical Investigation is to detect and.
locate subsurface geological structures or masses. During the
investigation, measurements of variations In subsurface properties
are obtained* These data are analyzed to surmise the causes of the
variations. Geophysical methods used for fault studies may include
seismic refraction, seismic reflection, magnetism, resistivity, or
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gravity* These methods are described In standard textbooks on
applied geophysics.
Exploratory excavations are the most positive and detailed
method to establish the location and activity of faults on a given
site. The exploratory excavation Is commonly made by a backhoe, a
dozer, or some other means of exposing the subsurface materials.
Selection of the excavation equipment depends upon accessblllty,
depth of excavation, difficulty of excavation, cost, length of time
the excavation Is to remain open, and the environmental Impact of the
excavation.
The purpose of the excavation Is to expose the subsurface
materials to a depth sufficient to enaule geologists to make a
detailed inspection and evaluation of the excavation walls to
determine if there are any fault features. In order to ensure that
the maximum amount of Information is obtained from each excavation,
the following procedures are necessary:
• The excavation should be perpendicular to the trend of known
faults, Lin eations, or suspicious features since faults
generally occur parallel to other faults. Thus, maximum
coverage can be obtained by perpendicular trenches.
• The excavation should be at le. 3t 10 to 20 feet deep. It is
necessary to excavate the tren i below the depth influenced
by man-made activities and soil processes and to locate
materials that will show fault offset. Generally, at these
depths, the strata are older and will show any fault offset.
These strata also aid in determining the recency of fault
activity.
• The excavation must be constructed with worker safety in
mind; it must comply with local, state, and Federal
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requirements for saiet7 and permits. For instance, it say be
required that the excavation be shored or vails layed back.
• The trench should be inspected and logged (see Figure 3) by
individuals experienced in logging fault features la test
trenches. Since some of the significant fault features are
difficult to recognize, experience is Invaluable.
• Sufficient time should be allowed to inspect and log the
excavation. Once the excavation is backfilled, the
excavation log is the only evidence available. Therefore, it
is very important that the log refleet the actual conditions
observed in the excavation. The graphic log should show
scale, tha length and depth, of the trench, the contacts
between various subsurface oaterlals, representative strike
and dip of bedding or joints, faults and shears, lithology,
and. continuous oafsuited material within the lenth of the
trench. See Figure 3, Taylor and Cluff (1973), and Sleamons
(197-7) for examples of trench logs.
•• The excavation, or series of excavations, should extend to a
distance on either side of the fault and the proposed
structure to identify and parallel fault planes. Generally
more than one excavation should be made across a fault or
suspected fault to conclusively determine its location and.
relative activity. The number of trenches will depend on
size of the facility (small-large), tectonic environment
(active-inactive), style of faulting (strike-slip, normal, or
reverse), type of surface materials (Rock-Eolocene
materials), and results of initial trenching (simple*
complex). One trench might be sufficient for a small site
with a simple, narrow, vall-deflned fault la the subsurface;
well-recognized surface features;, and continuous Holocene
deposits. At least two trenches should be used at large
sites; sites ulth.no evidence of subsurface faulting, but
surface lineatlons or Holocene faults within 300 feet; a wide
or complex fault pattern; a. fault that changes width,
direction, or pattern; or thrust or normal type faults.
Three, four, or more trenches may be needed to adequately
locate a fault zone across a site, show that the site is
usfaolted, and show that any faults that cross the site have
not had Holocene displacement.
The logging of exploratory excavations and the observations of
"active" faults la test trenches is discussed by Taylor and Cluff
(1973).
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ZOHg OF 6BOUNO gUPTUgf ON
WEST FAULT TRACS IB fUT WIDE
?PW OF TTLTTWIt TW
-------
Exploratory trenches have been used with increased frequency for
fault investigations. These trenches provide a better view of the
nature of the fault than can be obtained from a study of the ground
surface. The trenches allow examination of surface soils above a
fault and can provide an opportunity to assess the relative movement.
4.2 Information in Part B of the RCRA Permit
The results of the geologic study should be presented In a
report signed by the geologist(s) responsible for the study, and the
contents should be of a quality acceptable to a geologist experienced
in identifying and evaluating faults. Contents of the report should
include, but not be limited to, the following:
Location and map of study area
0 Sources of available data
• List.* of key scientists/engineers conducting study
r Description of geologic setting and site conditions
» Investigative methods and approaches
Aerial photographs or remote sensing images interpreted
(type, scale, source, index number)
» Logs of subsurface exploration (shoving.details, not
diagrammatic), if appropriate
• Geologic site map with exploration locations (1" • 200 feet,
for example), If appropriate
#¦ Regional geology map (1" ¦ 2000 feet, for example)
• Results, conclusions, and basis of findings
• References cited
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• Signature of geologist(s) responsible for conducting the
study.
Each step of the study will need to be documented for the permit
writer. The above contents provide an outline of that documentation.
'2-37
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5.0 REFERENCES
Botxllla, M. G., 1967. Historic Surface Faulting In Continental
United States and Adjacent Parts of Mexico. U.S. Geological Survey
TID-24124.
Bonllla, M. G., 1970. Surface Faulting and Related Effects. Chapter
3 in Earthquake Engineering (R. L. Wiegel, Editor). Prentice-Hall,
Division of Mines and Geology Special Publication 42, Revised March
1980.
California Seismic Safety Commission, 1979. Goals and Policies for
Earthquake Safety in California. SSC 79-04.
Cluff, L. S., 1968. Urban Development Within the San Andreas Fault
System, Proceedings of a Conference on Geologic Problems of the San
Adnreas Fault System. In Dickenson, W. R., and A. Gantz, editors,
Stanford University Publications, Geological Sciences, v. II. School
of Earth Sciences, Stanford University, California.
Cluff, L. S., and G. E. Brogan, 1974. Investigation and Evaluation
of Fault Activity in the U.S.A. Second International Congress of the
International Association.of Engineering Geology, Sao Paulo, Brazil.
Cluff, L. S., D. B. Slemmons, and E. B. Waggoner, 1970. Active Fault
Zone Hazards and Related Problems of Siting Works of Man. Proceeding
of the Fourth International Symposium on Earthquake Engineering.
Roorkee University, India. Indian Society of Earthquake Technology
Bulletin. 761. 1:401:410.
Earthquake Engineering Research Institute, 1980. Imperial County,
California, Earthquake of October IS, 1979. Berkeley, California.
Murphy, L. M., 1973. San Fernando, California, Earthquake of
February 9, 1971. In Volume II, Utilities, Transportation and
Sociological Aspects, U.S. Department of Commerce.
Rogers, T. H., 1973. Fault Trace Geometry Within the San Andreas and
Calaveras Fault Zones - A Clue .to the Evolution of Some Transcurrent
Fault Zones. In the Proceedings of the Conference on Tectonic
Problems of the Amos Hur, Stanford University Publications,
Geological Sciences, v. 13. School of Earth Sciences, Stanford
University, Stanford, California.
Sherard, J. L., L. S. Cluff, and C. R. Allen, 1974. Potentially
Active Faults in Dam Foundations. Geotechnlque, v. 24, No. 3, p.
367-428.
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Siemens, D. B., 1969. New Methods of Studying Regional Seismicity
and Surface Faulting. Transactions of the American Geophysical
Union, Vol. 50:397.
Siemens, D. B., 1977. Faults and Earthquake Magnitude,
State-of-the-Art for Assessing Earthquake Hazards In the United
States. U.S. Any Engineer Waterways Experiment Station
Miscellaneous Paper 5-73-1, Vicksburg, Mississippi.
Swan, F. H., D. P. Schwartz, and L. S. Cluff, 1980. Recurrence of
Moderate-to-large Earthquakes Produced by Surface Faulting on the
Wasatch Fault Zone,. Utah: Bulletin of the Saismalogical Society of
American, v. 70, No.5.
Taylor, C. L., and L. S. Cluff, 1973. Fault Activity and its
Significance Assessed by Exploratory Excavation. Conference on
Tectonic Problems on the San Andreas Fault- System Proceedings,
Geological Sciences, v. 13, School of Earth Sciences, Stanford
University, Stanford, California.
Taylor, C. L., and L. S. Cluff, 1977. Fault Displacement and Ground
Deformation Associated with Surface Faulting: Current State of
Knowledge of Lifeline Earthquake Engineering Proceedings, ASCE, Los
Angeles, California.
Taylor, C. L., and. L» S. Cluff, 1978* Geologic/Seismic Hazards
Evaluation, Fairmont Hospital - Juvenile Hall, San Laaadro,
California. Report Prepared for Alameda County Public Works Agency,
Hayward, California.
Taylor, C. L., and L. S. Cluff, 1978. Geologic/Seismic Hazards
Evaluation, Fairmont Hospital - Juvenile Hall, San Leandro,
California. Report Prepared for Almeda County Public Works Agency,
Hayward, California.
U.S. Environmental Protection Agency, 1980.' Background Document:
General Facility Standards for Location of Facilities (60 CFR 264,
Subpart B, Section 264.18). MS. 1941.34.
U.S. Environmental Protection Agency, 1981. Standards Applicable to
Owners and Operators of Hazardous Wiste Treatment, Storage, and
Disposal Facilities, 40 CFR Part 264. Federal Register, 46 FR 7:
2802. January 12.
U.S. Geological Survey and National Oceanic and Atmospheric
Administration, 1971. The San Fernando, California, Earthquake of
February 9, 1971. U.S. Geological Survey Professional Paper 733.
2-40
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Wallace, R. E., 1968. Notes on Scream Channels Offset by the San
Andreas Fault, Southern Coast Ranges, California. Conference on
Geologic Problems of the San Andreas Fault System Proceedings. In
Dickenson, W. R., and A. Gantz, Editors, Stanford University
Publications, Geological Sciences, v. 11, School of Earth Sciences,
Stanford University, Stanford, California.
Ziony, J. I., C. M. Wentvorth, and J. M. Buchanan, 1973. Recency of
Faulting:. A Widely Applicable Criterion for Assessing the Activity
of Faults. Fifth World Conference on Earthquake Engineering (June
1973), Rome, Italy.
•2w41
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APPENDIX A - GENERAL DISCUSSION OF EARTHQUAKES AND FAULTING
CAUSES OF EARTHQUAKES
There Is no one cause of all earthquakes. A minor cause of
earthquakes Is volcanic activity. Some deeper earthquakes may
perhaps be related to sudden changes in rock properties due to motion
deep within the Earth's mantle. However, most destructive,
shallow-focus earthquakes appear to be associated with a sudden
rupturing (faulting) of the Earth's crust1. The resulting
earthquakes are caused by the sudden release of accumulative strain
energy. The rupture, or break, is called a fault and is generally
accompanied by displacement of blocks either vertically or
horizontally or both on opposite sides of the fracture.
The seismic waves that are generated when the fauxt ruptures
arise from the movement of the rocks In the vicinity of the fault.
SIZE OF EARTHQUAKES
Two measures of earthquakes size, intensity and magnitude, have
been found to be useful. Unfortunately, these terms are often
confused and sometimes even used synonymously. Magnitude attaches a
single number that is independent of the distance from the earthquake
center and independent of geological and soil conditions to an
earthquake. For a measure of the variation of ground motion from
*"The crust is a rock layer of varying thickness, ranging from 30
miles under the continents to 3 miles under Che oceans, which is
found world-wide and is composed of mainly basaltic and granitic
rocks.
"2-4 3
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point to polar, as intensity scale Is used. The intensity value is
assigned by an experienced observer using a descriptive scale. Both
measures are too simple to describe the full complexity of an
earthquake and should be used Judiciously.
Intensity Scales
Intensity is a rating of the severity of the ground motion at a
specific location. The scale of measurement is based upon the
sensations of persons, the behavior of natural objects, and the
physical damage to natural and man-made objects. Intensity scales
came into being long before magnitude scales because intensity does
not require instrumental observation. Over the years, different
Intensity scales have been devised. The scale must reflect the
geologic setting of a particular region. The most widely accepted
intensity scale In the United States is the Modified Mercalli
Intensity Scale. It goes from I to XXX on a twelve-point scale.
Intensity ratings are bound to be subjective, as reported
intensities may take on several meanings, depending on who reports
them and the type of construction in an area. The reported Intensity
may be the nrnffTtmrn intensity at the bullt-op area nearest the
epicenter, or it may be what that intensity should have been at the
epicenter based on observations at a center of population some
distance away. Many circumstances arise that make it difficult to
assign intensities. The lack of precision in the intensity
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should be recognized. Basically, intensity refers to the measures of
earthquake effects of all types at a specified place. It is not
based on true measurement, but it is a riting assigned by an
experienced observer using a descriptive scale.
Because intensity is defined by the observed effects on the
Earth's surface, such as landslides or broken underground pipes, the
intensity of an earthquake on a mid-oceanic ridge might be taken as
zero. On the other hand, a smaller shock centered near weak man-made
structures on poor ground might yield a high intensity. For a given
earthquake, intensity differs betveen localities depending upon the
distance from the source, the severity of the shaking, the duration
of the shaking, the geologic foundation, and the quality of design
and construction.
Magnitude Scales
Magnitude is based on ground motion as recorded by distant
seismographs. The most commonly used method of calculating magnitude
in the United States for moderate to large earthquakes is that of
C.F. Richter. Other magnitude scales are, however, widely used by
seismologists, both in the United States and in other countries,
sometimes leading to what appear to be conflicting magnitudes. To
briefly illustrate the technique used to calculate a magnitude for an
earthquake consider the following case. A particular kind of
seismograph (called a Wood-Anderson instrument) at a distance of
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about 62 miles (100 kilometers) from the epicenter records the
earthquake ground motion. The recording is called a seismogram.
Using a ruler with a centimeter scale, the half-width ("amplitude")
4
of the largest wave is measured and coverted to microns (10
microns ¦ 1 cm). The logarithm (to base 10) of this number is the
Richter magnitude of the earthquake. For example, if the maximum
aplitude measured is 1 cm, the Richter magnitude is 4.0. Empirical
tables provide the necessary adjustment when the seismograph Is at
various epleentral distances, when other types of seismographs are
used, for various focal depths, and for various types of vaves.
EARTHQUAKE-ASSOCIATED DAJ1AGE
Earthquake damage depends on many variables: earthquake
magnitude, epleentral location, depth of focus, duration of shaking,
intensity of shaking, near-surface soil and geologic conditions,
structural type, and design. Damage related to ground (or soil)
conditions depends upon <~vsurface properties such as material
density, shear strength, thickness, and water level.
Earthquake-associated damage is usually manifest in three
separate forms: (1) fault displacement, (2) strung ground motion
(shaking), and (3) ground (or soil) failure.
FAULTING
Faulting, as the movement or fracturing along faults is called,
may have horizontal and vertical components of displacement and may
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vary from a fraction of an Inch to many feet. In the California
earthquake of April L8, 1906, horizontal offsets along the San
Andreas fault averaged from 8 to 15 feet and extended from just north
of San Juan Batista to north of Point Arena, a distance of more than
200 miles.
Fracturing and shearing associated with faulting are often
observed in the field to be of a multiple and en echelon character,
with several planes of displacment being formed through geologic time
(millions of years); thus the term "fault zone" is a more realistic
designation. The exact location and characteristics of a fault zone
are of vital concern in estimating the hazard from faulting. Once a
fault is formed, it constitutes a plane of weakness that localizes
further adjustments.
Some fault zones, such as the San Andreas fault, are more than a
mile vide in places, containing many "fault traces" within the broad
zone. On might ask, "What is the relative risk of developing or
locating structures within such a wide active fault zone?" It
depends upon factors such as type of development, intended land use,
type of structure, and site location with respect to the active fault
traces. The broad fault zones have been formed over long periods of
geologic time, and in some future geologic time (millions of years)
not only may the present fault traces be reactivated, but new traces
may be formed. However, if we consider this problem from the
• 2-47
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standpoint of "engineering design time" (on the order of 100 years),
the probability of fault movement is ouch high along the more
recently active fault traces that lie within the broad fault zone.
Types of Surface Faulting
Surface faulting can generally be divided Into three types
(Bonilla, 1967): main fault, branch fault, and secondary fault as
shown on Figure 2 (test). The main fault is actually a band of
varying vidth, which includes closely spaced faults that are the
location of the major surface displacement and associated faults that
decrease rapidly in number and amount of displacement away from the
location of major fault displacement.-'The main fault trace is the
surface fault with the greatest displacement, length, and
continuity. The main fault trace generally receives the greatest
consideration because the amount of fault displacement and the width
of the bend of faulting are greater than with the other two
.categories of faulting.
A branch fault generally originates as part of a main fault, but
laterally it diverges from and extends well beyond the main zone of
faulting. The branch fault generally shows the same type of
displacement as the main fault and either joins it at 'be surface or
is Inferred to join In the subsurface. While branch faults may form
during surface faulting and may be found associated with the main
fault at several locations along its length, branch faults do not
•2-48
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exist along a major part of the main fault's length nor do they
result in a continuous zone of faulting from the main fault trace out
to the branch fault trace.
Secondary faults are completely separated spatially from the
main fault trace and from the branch fault trace. Secondary faults
occur infrequently and generally consume a very small percentage of
the total fault length.
When considering the potential for future surface faulting, it
is important to remember that a continuous band of faulting is likely
along the main fault trace; branch faults may occur adjacent to the
main faulting but only along a small percentage (about 20 percent) of
the total fault length and the width of faulting is generally
smaller; and secondary faulting is a relatively rare event along a
very small percentage of the total fault length (about 5 percent)t
and the amount and width of faulting is generally much smaller. Even
in those cases where the surface faulting consists of a main fault,
branch faults, and secondary fauls, this does not represent a
continuous zone of faulting, but a zone in which the three types of
faulting occur as restricted bands of varying width with considerable
unfaulted material in between the bands as shown in Figure 2 (text).
The - important consideration is not the distinction between the types
of faulting (main fault, branch fault, or secondary fault) nor the
width In which these categories of faulting may occur, but the actual
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width of the fault zone adjacent to a proposed structure and, more
specifically, the distance between the structure and any fault.
Width of Surface Faulting and Defornation
Surface fault rupture along a fault trace may be accompanied by
displace. r>r along the individual faults and by horizontal or
vertical deforaation (distortion or warping) of the ground surface
extending from soma distance on either side of the fault trace. The
occurrence and the amount of deformation depend upon the type of
faulting, the amount of fault displacement, and the properties
(strength, type, and depth) of materials at specific sites along a
fault trace.
On the basis of statistical analysis of historical earthquakes,
Boni1la (1970), reports that at least half of the historical faulting
events In North America include subsidiary faulting (i.e., branch
and/or secondary faulting). If one were to take the historical
faulting data presented by Bon11la (1970) at face value, it could be
inferred that the main zone of faulting could be up to 917 meters
(3,000 feet) vide; the zone of branch faulting could be up to 4.8-
kUoaeters (3 miles) wide, and the zone of secondary faulting could
be up to 14.5 (9 miles) vide—all measured from the center line of
the faulting. However, these data refer to the composite zone In
which these different categories of faulting occur and not to a
continuous zone of faulting along the entire length of the surface
*-50
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faulting. Such an interpretation of these data gives an erroneous
and overly pessimistic viev of the potential width of surface
faulting and,, therefore, the impact upon adjacent structures. Based
on a review of historical earthquakes and reported surface faulting,
reconnaissance and interpretation of aerial photographs along faults
that have had displacement within historic times, and review and
examination of test trenches excavated across faults that have had
displacement during historic times, it is concluded that the width of
faulting and associated ground deformation generally ranges from
several feet to as much as several hundred feet (Taylor and Cluff,
1977).
Taylor and Cluff (1978) reviewed fourteen cases of documented
deformation associated with the 1906 faulting along the San Andreas
fault (a strike-slip fault) near San Francisco, California. From
those data it was concluded that the width of the faulting and
deformation ranges from 3 meters (10 feet) to 211 meters (690 feet),
including 3 cases (212) having a width greater than 61 meters (200
feet), 3 cases (21%) having a width between 30.5 and 61 meters (100
to 200 feet), and 8 cases (58%) with a width less than 30.5 meters
(100 feet). It was also concluded that at distances greater than
about 61 meters (200 feet) the deformation is generally
insignificant. It is very important to emphasize that the
deformations were associated with a fault that had displacements
"S-51
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ganging from 12 eo 20 feet horizontally, and the width of faulting
and deformation would be less for surface faulting events with
displacements of lesser amounts.
A recent study at two sites along the Wasatch fault In Utah (a
normal fault with vertical displacement) by Swan, Schwartz, and Cluff
(1980) reports that: (1) the fault has had accumulative vertical
displacement an the order of 10 to 13.5 meters (33 to 44 feet) during
about the last 12,000 to 13,000 years (within Holocene time), (2) the
width of faulting is about 68 meters (222 feet), and (3) the width of
deformation is about 120 meters (392 feet), i.e., it extends about 52
meters (170 feet) beyond the limits of faulting.
Based on exploratory excavations across Holocene faults, the
following general comments are made by Taylor and Cluff (1977):
» "Surface faulting is generally confined to narrow
fault-traces in a wider zone of disturbance. The width of
the fault-traces can range from a few feet to several tens of
feet and is dependent on the type of faulting, amount of '
faulting, and geometry of the fault plane. Many times the
major surface faulting and fault displacement occur along a
single fault-trace which is referred to as the main
fault-trace."
» "The zone of disturbance can have a width of from a few feet
up to more than 50 feet and frequently has a width of several
hundred feet. This zone of disturbance Includes the
Individual fault-traces (or main fault-trace) and auxUliary
or secondary cracks branching obliquely from or lying
parallel to the fault-traces."
» "Surface deformation and distortion of structures is
frequently reported within a zone several tens to several
hundreds of feet wide adjacent to the surface faulting and
within the zone of disturbance."
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• "The geologic and historic record of fault activity
demonstrates that the\location of future' surface faulting
will most likely occur on or near the most recently active
fault-trace."
• "For an engineering project or structure located across or
in the vicinity of a fault, the primary consideration Is the
possibility of recurrent movement on that fault within a time
period which is considered significant to that project or
structure."
A review of the above data will show that while the width of
surface faulting and deformation may in some cases be several
thousand feet wide, it generally ranges from a few feet to several
hundred feet. However, the major consideration should not be the
width of the zone of faulting but the distance from the fault that
has had Holocene displacement.
Strong Ground Motion (Shaking)
Damage from strong ground motion (shaking) is caused by the
transmission of earthquake vibrations from the ground into the
structure. The main variable factors that determine the extent of
vibrational damage are: characteristics of ground, design of
structure, quality of materials and construction, and intensity and
duration of shaking. During moderate to large earthquakes, it is the
strong shaking that usually inflicts the most damage to man-made
structures..
Damage from Ground Failure
Damage from ground failure may occur In several different forms,
such as landslidlng, liquefaction, lurching, settlement, and
selsaically Induced flooding.
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It Is common for earthquake-triggered landslides to occur as
renewed movements of old landslide deposits. Areas subject to slope
Instability could be subject to earthquake-triggered landslides.
Liquefaction occurs when granular, essentially cohesionless
soils undergo loss of shear strength due to the buildup of fluid
pressures In the soil pore water (caused by cyclic loading during
earthquakes). When the loss In strength is low to moderate, partial
liquefaction may cause ground settlement and associated ground
cracking. However, when liquefaction is complete, the soil can
behave as a fluid, and catastrophic failures. Including soil flows
and landslides, have occurred as a result. Partial liquefaction
during strong ground shaking may occur In dense to very dense
cohesionless soils; complete liquefaction typically occurs only In
loose to medium dense cohesionless soils.
Seismic settlement is. also associated with cohesionless soil
deposits in poorly placed or uncompacted man-made fill. The strong
ground shaking that occurs during earthquakes will densify loose
granular soils. When these soils are above the groundwater table,
their denslflcatlon and resulting ground subsidence will occur
rapidly. When located below the groundwater table, the pore water
pressures that have developed during the shaking must begin to
dissipate before a decrease in soil volume can occur and, as a
result, settlement occurs at a rate commensurate with.the flow of
water from the cohesionless soil layer.
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Lurching may be generally defined as the development of all
types and sizes of irregular ground fractures, cracks, and fissures
associated with shaking, settling, and the passage of surface waves
during earthquakes. In this general sense, ground cracks that occur
as a result of liquefaction, compaction, settlement, or landsliding
may be termed "lurch cracks". More specifically, lurching involves
the seismlcally induced lateral movement and spreading of ground
toward a "free face," together with the development of associated
tension cracks in the ground behind the free face.
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APPENDIX B - FAULTING AND GEOMORPHIC FEATURES OF FAULT ZONES
The three mala types of faults considered vlthin this discussion
are strike-slip, normal-slip, and reverse-slip faults. Each of these
three types of faults is characterised by a distinctive type of
movement and geometry. A discussion of these fault types follows.
Strike-Slip Fault
A strike-slip fault (Figure 4) Is one in which displacements are
essentially parallel to the strike of the fault; the movement is
primarily in a horizontal direction with little vertical
displacement. The fault planes on strike-slip faults are most often
nearly vertical. Strike-slip faults are of two types: right-lateral
and left-lateral. In a right-lateral fault the displacement is such
that, in plan view, the side opposite the observer appears displaced
to the right. In a left-lateral fault this displacement appears to
the left. Strike-slip faults -are common in an environment subject to
compression of blocks or plates. Depending on their orientations,
structures across or in the vicinity of a strike-slip fault can be
subject to compression, extension, displacement, or distortion.
Normal-Slip Faults
A normal-slip fault (Figure 4) is one in which one side has
moved downward relative to the other side* The movements may involve
vertical components only or combinations of vertical and horizontal
displacements. The angle of the fault plane In normal-slip faults Is
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STRIKE-SUP
MAY HAVE A
VERTICAL COMPONENT
IN EITHER DIRECTION
NORMAL-SLIP
MAY HAVE
STRIKE-SUP
COMPONENT IN
EITHER DIRECTION
v»- -Jr.
MAY HAVE
STRIKE-SLJP COMPONENT
IN EITHER DIRECTION
REVERSE-SUP
SOURCE: Ttvlor and duff, 1977
FIGURE A
THREE TYPES OF FAULT DISPLACEMENT
•2-58
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generally 45° to 90*, and these types of faults generally form in a
tenslonal environment characterized by a lengthening of the earth's
crust. The zone of faulting Is more pronounced and wider on the
downthrown (lower) side, although the fault displacement and slope
Instability appear more dramatic on the upper side about the steep
fault scarp.
Reverse-Slip Faults
A. reverse-slip fault (Figure 4) Is one in which the upper block
appears to have moved upward relative to the lower block. As in
normal-slip faults, the movement of reverse-slip faults may involve
vertical components only or a combination of both vertical and
horizontal dispU :ements. The fault plane of reverse-slip faults
dips at an angle of 45° and less and generally forms in a
compressionable environment characterized by a shortening of the
crust.
Of primary importance In the Identification, characterization of
length and type of movement, and assessment of future rupture
patterns in active fault zones is the study of fault-related
geomorphic features expressed at the earth's surface (Slemmons,
1977). Each el le three fault types discussed above exhibits
characteristic geomorphic features, with strike-slip faults
exhibiting the simplest features and reverse-slip faults exhibiting
the most complex. The morphology varies from small scale features to
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large-scale geomorphic features chat form the mala topographic
expression of the faulting. The following is a brief discussion of
the main geomorphic features associated with each of the three fault
types.
Landforms associated with strike-slip faults reflect the
primarily lateral sliding of opposing blocks past one another, with
branch faults and en echelon configurations common and characterizing
the fault 2one as an area o£ multiple blocks with complex lateral
sliding relations. As opposing blocks slide laterally, some blocks
are relatively depressed to form.sags or sag ponds, or elongated
graben may form between parallel breaks. Other slivers are raised,
tilted, or slid diagonally to produce Imolls and shutter ridges;
elongated horsts may be uplifted between traces~ Notches and
trenches or troughs along the fault may reflect increased erosion of
the crushed or broken rocks, or they may be primary features. The
most prominent Indicator of vertical movements and probably the most
useful in terms of recency of movement is the presence of and
freshness of scarps, which are often very long In extent; horizontal
shifts are probably best displayed by offsetting of drainage channels
and drainage related features. Typically, features associated with
strike-slip faults are In alignment with one another and define
lineations best observed from the air or in aerial photographs.
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Surface expression of faulting associated with normal-slip
faults is generally more complex than for strike-slip faults. In
general, normal-slip faults have.a large component of vertical
displacement and develop steep, high scarps. -Branch faults are
common and tend to transfer displacement to more than one fault, and,
In addition, the inclined nature of many of the fault planes provides
the possibility of faulting and secondary failures in surflcial
materials. Subsidiary faulting or disturbances are often restricted,
to the downthrown block. Sleamons (1977) describes the following
five features characteristic of normal faults:
• Simple Fault Scarps - Surface rupturing along a single break
which extends to the earth's surface. The scarp in this type
of break represents the main fault plane.
• Fault Fissure Scarps or Fissure Trace - Formation of a near
vertical fissure at some distance back from the tip of the
•downthrowu block, this fissure branching off the main fault
plane. This type of break Is more often formed in
unconsolidated alluvial materials and the unstable nature of
the unconsolidated surfieal materials generally results in
slumping into the fissure.
• Trench Trace Scarps or Graben Fault-Trace Scams - These
scarps result from the gravitational failure of slump blocks
into the fault fissure described above. The slumps may occur
on either side of the fault fissure.
• Longitudinal or Step Trace Scarps - These scarps result from
one or more slump blocks on the uphill side of the fault
fissures, resulting in a staircase arrangement.
• Subsidence Trace Faults or Scarps - This type of scarp
normally forms where the fault fissure Is filled by
semi-plastic flow of materials Instead of by slumping.
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The geomorphic features of reverse-slip faults are generally
more subtle and not aa easily distinguished as strike-slip and
normal-slip faults. In general, the low. c dip angles of the fault
plane result in less conspicuous, more irregular fault traces and
scarps of complex patterns. Often, nuae- "2us branch faults cut to the
surface from the main fault, resulting 1 complexly shattered surface
displacements. .The fault relations are further complicated and
obscured due to the formation of large landslides and gravity slips
in the upper block (Figure 4) as a result of the overthrusting. The
lowar block. In contrast, undergoes little distortion.
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APPENDIX C - HOLOCENE DEPOSITS AND ACTIVE FAULTING
The Holocene is generally defined as an epoch of the Quaternary
period extending frota approximately 11,000 years ago to the present
time. Holocene deposits are those formed within this time period,
during which climatic and sea level conditions and geomorphic
processes have been similar to or are ongoing with those now
prevailing. Holocene deposits primarily form In such environments as
floodplains; 'alluvial fans; coastal terraces; deltas in estuaries,
reservoirs, or bays; and mudflats or marshland. Deposits can also
form In relatively temporary depositional environments, such as in
stream channels or on adjacent beaches, as well as in areas
characterized by landsliding and landslide deposits.
Depending on such conditions as the physiographic and
climatologic regime, the type and degree of weathering, the relative
rates of erosion and deposition, and other factors, different areas
of the U.S. are characterized by relatively extensive or scanty
Holocene deposits. In areas where Holocene deposits are extensive,
observation of physiographic features to identify faults and to
assess the recency and types of movements is generally adequate. In
areas where Holocene deposits are scanty or formed in very localized
areas, fault-related features must be identified using older
Quaternary or Pre-Quaternary deposits.
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