Regional location in western China Page: 4 of 13
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REGIONAL LOCATION IN WESTERN CHINA
Allen H. Cogbill & Lee K. Steck
Earth & Environmental Sciences Division
Los Alamos National Laboratory
Los Alamos, NM 87545
Sponsored by DOE
Accurately locating seismic events in western China using only regional seismic stations
is a challenge. Not only is the number of seismic stations available for locating events small, but
most stations available to researchers are often over 100 distant. Here we describe the relocation,
using regional stations, of both nuclear and earthquake sources near the Lop Nor test site in
western China. For such relocations, we used the Earthquake Data Reports provided by the U. S.
Geological Survey (USGS) for the reported travel times. Such reports provide a listing of all
phases reported to the USGS from stations throughout the world, including many stations in the
People's Republic of China. LocSAT was used as the location code. We systematically relo-
cated each event in this study several times, using fewer and fewer stations at each relocation,
with the farther stations being eliminated at each step. We found that location accuracy, judged
by comparing solutions from few stations to the solution provided using all available stations,
remained good typically until fewer than seven stations remained. With a good station distribu-
tion, location accuracy remained surprisingly good (within 7 km) using as few as 3 stations.
Because these relocations were computed without good station corrections and without source-
specific station corrections (that is, path corrections), we believe that such regional locations can
be substantially improved, largely using static station corrections and source-specific station
corrections, at least in the Lop Nor area, where sources have known locations. Elsewhere in
China, we must rely upon known locations of regionally-recorded explosions. Locating such
sources is clearly one of the major problem to be overcome before we can provide event loca-
tions with any assurance from regional stations. Inasmuch as small events may only be detected
at regional stations, it is paramount to find such sources, as they represent "ground truth".
Key words: seismic, location, regional
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Cogbill, A.H. & Steck, L.K. Regional location in western China, report, October 1, 1996; New Mexico. (digital.library.unt.edu/ark:/67531/metadc680366/m1/4/: accessed August 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.