Department of Conservation
- California Geological Survey
- www.quake.ca.gov
- Turkey Flat Main Page
- Contacts
- Steering Committee
- Contributors
- Weak-motion Test Results
- References
- Links
- Turkey Flat Workshop
- Registration
- Schedule
- Ground Motion Data
- Geotechnical Site Data
- Standard Geotechnical Model
- Input Record Format
- Data Format for Predictions
CGS Links
Other Resources
Right Column
TURKEY FLAT, USA SITE EFFECTS
TEST AREA
Strong-Motion Test
This is the official website for the Turkey Flat “blind” strong-motion prediction test, based on recordings obtained by the CSMIP instruments in the Turkey Flat array during the September 28, 2004 M6.0 Parkfield earthquake. The purpose of the test is to validate current methods of estimating the effects of soil/ground conditions on earthquake shaking that are used in designing earthquake resistant structures. Nearly all transactions with participants in the test will be conducted through this website, including online registration and distribution of prediction criteria, input records, format standards, etc. References and reports regarding the Turkey Flat test site will also be made available through this site.
Overview of Turkey Flat Project
Goals:
Systematically compare and evaluate the reliability of
contemporary methods used to estimate the effect of surface
geology on, and to test the linearity of, shallow stiff-soil
site response.
Approach:
Collect high quality ground motion data from local earthquakes,
quantify the geotechnical properties of the site geology, and
distribute the information to experts in California and around
the world. Conduct “blind” prediction tests using predicted
calculations made by ground motion experts for sensor sites
where the response is known, but not made available until all
predictions have been received. Results of each prediction will
be compared with one another and with actual observed ground
motion. As with a similar test using weak-motion recordings in
1990’s, submitted calculations will be kept anonymous.
Products: A
database of weak and strong-motion records from the array, and
predictions based on a variety of ground motion models; a
database of geotechnical properties of the test area; a series
of reports describing each principal phase of the project (see
references); an analysis of all prediction results, including
statistical comparisons of the predictions and the recorded
data; and technical papers from participants.
Background: At
the 1985 General Assembly of the International Association of
Seismology and Physics of the Earth’s Interior (IASPEI), held
jointly with the International Association of Earthquake
Engineering (IAEE) in Tokyo, Japan, a resolution was passed
forming a Joint Working Group on the Effects of Surface Geology
on Seismic Motion (IASPEI/IAEE JWG-ESG). The purpose of the
group is to coordinate the establishment of an international
series of test areas designed to provide a database for
comparing and testing contemporary methods, and develop new
methods, to predict the effects of local geology on earthquake
ground motion. Although methods for assessing site effects are
being used in the design of critical facilities around the
world, the reliability of these methods has not been rigorously
tested. It is the goal of this program to fulfill this need. An
international program provides a forum for experts around the
world to exchange ideas, and significantly increases the
prospects for acquiring the necessary data much sooner than
would otherwise be possible. Recognizing the importance of the
effort to earthquake safety in California, in 1986 the
California Geological Survey established a test site at Turkey
Flat, California. At the XIX General Assembly of the
International Union of Geodesy and Geophysics in Vancouver,
British Columbia, 1987, a resolution was passed incorporating
the experiment at Turkey Flat into the international program.
Summary of Strong-Motion Test
Eighteen years ago, in anticipation of the Parkfield earthquake,
the California Geological Survey (CGS) established a test area
in a sedimentary valley at Turkey Flat, near Parkfield,
California, where the California Strong Motion Instrumentation
Program (CSMIP) installed a strong motion array. CGS partnered
with the IASPEI/IAEE Joint Working Group on Effects of Surface
Geology on Seismic Motion as well as members of the geotechnical
community to thoroughly characterize the geophysical properties
of the site. The strong motion array consists of surface and
downhole accelerometers, with surface instruments at the two
valley edges, at one quarter of the valley width, and at the
center of the small, shallow stiff-soil (25 m) sedimentary
valley. The instruments at the valley center also include a
downhole array, with instruments just beneath the rock interface
and at mid-height in the sediments.
The September 28, 2004 M6.0 Parkfield earthquake
was well recorded throughout the test site array, and this
provides the ground motion records necessary to conduct the long
awaited blind prediction test. In this prediction experiment,
acceleration time histories recorded on bedrock near one valley
edge will be provided along with a “standard” model of the
geotechnical properties at all recording sites to interested
participants. Participants will be asked to make predictions of
the ground motions at the five other recording locations (3
surface and 2 downhole), where, as part of a long-term plan,
recordings are being withheld by CSMIP until the predictions
have been received and officially logged. Details of the test
area and the test procedure will be distributed in an open
invitation for all interested parties to participate in the
blind test. A workshop at which predictions can be presented and
comparisons made with the recorded motions is planned for Fall
2005.
Click here for details of Test
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