Bay Area Earthquake Hazards Arrays

 We have deployed several dense arrays of Kinemetrics K2 accelerographs in the San Jose, California area to determine the effects of  sedimentary basins on ground motions in this high seismic-risk area so that strong shaking from future large earthquakes can be predicted more accurately. The instruments were purchased with funding from Pacific Gas and Electric Co.

  The San Jose array was installed beginning in February, 1999 and was operated intact until about May of 2004. Instruments were then gradually moved from San Jose to form other dense arrays in nearby Saratoga, CA, Los Gatos, CA, Milpitas, CA, and the Niles District of Fremont, CA.

  The San Jose array was located near the eastern edge of the Santa Clara Valley and had an average station spacing of 1 km forming equilateral triangles. This urban array was very successful at triggering on recording local and regional earthquakes. We have constructed maps of spectral amplitudes across the array that generally show higher amplitudes at stations farther from the eastern edge of the Santa Clara Valley, for the frequency range studied (0.125-8 Hz). We have produced computer animations of the long-period (2-8 sec) seismic waves as they cross the array. We observe basin surface waves traveling across the array from south to north for regional events located east of the array. It is remarkable that the largest long-period arrivals are basin surface waves traveling from a direction 70 degrees from that to the epicenters. We find that 3D finite-difference simulations generally reproduce the major features of the observations.

   The data are organized into event folders with the SAC format station data in those folders. Only events that triggered 10 or more array stations are saved in the folders.  The headers of the records have been corrected using the Header Data file that is included in the directory. The Catalog Locations file in the directory contains either the Northern California Earthquake Catalog location or the USGS/NEIC location for the associated event, the number of array stations that recorded the event and the associated event files name. We have also included the Associated Event file primarily for use as an indicator of timing accuracy. The field immediately after the tab indicates the number of hours since the last GPS lock. Our tests indicate that the K2’s timing accuracy is within 2 ms if the last lock was within 2 hours of the event recording. Fortunately, almost all of the data has a lock within 2 hours.

  Please feel free to contact us with comments or questions.


David Carver 
carver@usgs.gov
(303)378-2910