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A Search for Temporal Variations in Station Terms in Southern California from 1984 to 2002

Guoqing Lin, Peter M. Shearer, & Egill Hauksson

Published 2008, SCEC Contribution #1123

We use relative arrival times and locations for similar earthquake pairs that are found by using a cross-correlation method to analyze the time dependence of P and S station terms in southern California from 1984 to 2002. We examine 494 similar event clusters recorded by Southern California Seismic Network (SCSN) stations and compute absolute arrival-time variations from the differential arrival-time residuals obtained following event relocation. We compute station terms from the robust means of the absolute arrival-time residuals from all events recorded by each station at 3-month intervals. We observe 9 stations with abrupt offsets in timing of 20 to 70 milliseconds, which are likely caused by equipment changes during our study period. Taking these changes into account could improve the relative location accuracy for some of the event clusters. For other stations, we generally do not see systematic temporal variations greater than about 10 ms. Analysis of residuals along individual ray paths does not reveal any localized regions of apparent velocity changes at depth. These results limit large-scale temporal variations in P and S velocities across southern California during this time period to less than about 0.2%. However, there is an increased fraction of travel-time residuals exceeding 20 ms immediately following major earthquakes from source regions near the mainshock rupture.

Key Words
United States, p-waves, body waves, statistical analysis, elastic waves, variations, California, Southern California, seismicity, crosscorrelation, temporal distribution, seismic waves, algorithms, seismic networks, arrival time, earthquakes, s-waves

Lin, G., Shearer, P. M., & Hauksson, E. (2008). A Search for Temporal Variations in Station Terms in Southern California from 1984 to 2002. Bulletin of the Seismological Society of America, 98, 2118-2132. doi: 10.1785/0120070243.