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Published 2002 | Published
Technical Report Open

Report for passive data acquired in the 1998-1999 Los Angeles Region Seismic Experiment II: a transect from Santa Monica Bay to the Westernmost Mojave Desert

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Between October, 1998 and April, 1999, 83 seismic stations were installed in the greater western Los Angeles, California area to record teleseismic, regional, and local earthquakes. The near-linear 93-km long array extended between Santa Monica Bay and the western Mojave Desert, through the epicentral region of the Northridge earthquake. The goals of the experiment were to determine crustal thickness below the western Transverse Ranges, San Fernando Valley basin, and western Mojave Desert, measure anistropy along the line with special emphasis on the San Andreas fault region, evaluate the potential for future strong ground shaking at sites in the basins, and determine the kinematic relationship between crustal and uppermost mantle deformation by three-dimensional tomographic inversion using regional network data combined with the array data. The stations consisted of three-component, broadband and short-period seismometers, and timing was controlled by Global Positioning System (GPS) receivers. The array recorded 165 Gb of raw waveform data in continuous (25 sps) and triggered (50 sps) streams. Approximately 144 teleseismic earthquakes with magnitudes ≥ 5.5, and 2025 local earthquakes with magnitude ≥ 2.0 were recorded. Preliminary results from three-dimensional teleseismic traveltime inversion tomography indicate that uppermost mantle seismic anomalies strongly correlate with thickened crust in the Transverse Ranges suggesting that the width of the compressional region and convergence rate control the location of deformation more than the San Andreas shear zone does.

Additional Information

The 1998-1999 Los Angeles Region Seismic Experiment II was made possible by the generous help of many volunteers many of whom spent multiple days in the field installing and picking up seismic equipment. We extend our thanks and appreciation to S. Baher, J. Behr, R. Clayton, J. Deng, B. Dollar, J. Franck, G. Fuis, D. Given, C. Glavich, K. Hafner, H. van Heijst, S. Hough, D. Icenogle, E. Jewel, C. Ji, K. Kähler, N. King, H. Kumagai, N. LeFleur, J. Mori, J. Murphy, A. Nguyen, N. Oerlemans, J. Ritsema, P. Roberts, J. Rubenstein, J. Santillan, N. Scheckel, S. Schwarz, S. Van Wyk, M. Watkins, C. Woodruff, and L. Zhu. We especially thank the IRIS PASSCAL and SCEC PBIC staffs who aided with the station design, installation, and testing, and with data processing. The staff includes M. Alvarez, N. Barstow, P. Friberg, I. Macham, A. Martin, R. Sell, and M. Templeton. The equipment loan and maintenance were made possible by the existence of IRIS PASSCAL and the SCEC PBIC. This research was supported by the Southern California Earthquake Center. SCEC is funded by NSF Cooperative Agreement EAR-8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. The SCEC contribution number for this report is 631.

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August 19, 2023
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