obtaining and reviewing these maps, government
presence in the landscape indicates geologically
geologists who may be actively working on the
recent tectonic activity.
geology of the area including the site should be
contacted as needed.
It has experienced at least one episode of surface
$
rupture (including fault creep) during
$ A review of topographic maps available from the
approximately the past 11,000 years (Holocene
U.S. Geological Survey. These maps depict the
time) or multiple episodes of rupture during the
topography in the general site vicinity and can be
last 100,000 years (the late Quaternary period).
used to identify geomorphic features that might
indicate the presence of faults.
(1) Regional potential for surface fault rupture. The
potential for surface fault rupture varies greatly in
$ A reconnaissance of the site and review of aerial
different parts of the United States. The potential exists
photographs. With respect to the surface fault
mainly along and near the active deformation boundary
rupture hazard, a site reconnaissance and review
between the North American and Pacific tectonic
of available aerial photographs, aimed at
plates, which extends along coastal California, Oregon,
detecting geologic or geomorphic evidence of
Washington, and southeastern and southern Alaska.
faulting, should be conducted if adequate geologic
The tectonic effects of this plate boundary, including
and topographic maps are not available.
surface faulting, extend to the eastern margin of the
Rocky Mountains. Beyond the plate boundary,
(3) Screening criteria. It can be assumed that a
intraplate earthquakes occur within the North
severe hazard due to surface fault rupture does not exist
American plate but generally have not been
at the site if, based upon a review of the available
accompanied by surface fault rupture. In the eastern
information, both of the following screening criteria are
United States, the only active faults that have been
met:
mapped at the ground surface to date are the Meers and
Criner faults in southern Oklahoma. These faults,
(a) Geologic and topographic maps show no faults
which comprise two segments of the Frontal Wichita
passing beneath the site or in the vicinity of the site; or
Fault System, have well developed geomorphic
if the maps show faults and folds in the vicinity of the
expression and geologically documented episodes of
site, the geologic maps and related cross sections
slip during Holocene time. Intraplate earthquakes
clearly show that earth materials that are as least as old
within the Pacific plate occur beneath the state of
as Quaternary (1.8 million years old), like soils,
Hawaii and are triggered by the underground
alluvium, terrace surfaces and/or deposits, lie across
movement of basaltic magma from which the island
the folds and faults and are not deformed by them.
volcanoes have been built. Ground fissuring can occur
due to the swelling of volcanoes prior to eruption.
(b) Site reconnaissance and air photo review does
not detect evidence of faulting at the site.
(2) Steps involved in screening. Screening for
surface fault rupture should include:
(4) Example. An example of screening for surface
fault rupture potential is given in Appendix G.
$ A review of geologic maps available from the
U.S. Geological Survey, state geological
agencies, and local government agencies. The
b. Soil liquefaction. The potential for experiencing
geologic maps typically show the location of
liquefaction (or not) at a site during an earthquake is
faults and identify the ages of the geologic units
primarily influenced by the characteristics of the
displaced by the fault. Large-scale geologic maps
subsurface soils (e.g., geologic age and depositional
(e.g., 1:24,000 or larger scale) prepared within
environment, soil type,
the last 30 years generally provide the most
reliable information for this type of assessment.
In California, "Alquist-Priolo" maps, published by
the California Division of Mines and Geology,
define those zones within the state in which
surface fault rupture is a significant risk. The
U.S. Geological Survey in Denver is currently
preparing maps that show the major active faults
in the Western Hemisphere. In the process of
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