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Southern California Permanent GPS Geodetic Array: Continuous Measurements of Crustal Deformation in the Los Angeles Basin between the 1992 Landers and 1994 Northridge Earthquakes

Yehuda Bock, Matt van Domselaar, Peng Fang, & Kenneth W. Hudnut

Published 1998, SCEC Contribution #382

We investigate the time series of daily positions estimated for two continuously Global Positioning System (GPS) sites in the Los Angeles region in the 19-month period between the 1992 Landers and 1994 Northridge earthquakes. The site at the Jet Propulsion Laboratory in Pasadena (JPLM) was active througout the 19-month period; the site on the Palos Verdes Peninsula (PVEP) was activated only nine months before the Northridge earthquqke. A comparison of the post-Landers site velocities with those derived from Global Positioning System (GPS) and very long baseline interferometry measurements collected over 5-8 years prior to the earthquake indicate a significant change in the displacement rate at JPLM. The velocity difference after the Landers earthquake is manifested primarily as a decrease in magnitude of about 2 mm/yr in a direction nearly coincident with the direction of coseismic surface displacement. Since the same pattern of deformation is observed over a wide-aperture in southern California we infer that the entire Los Angeles basin experienced postseismic deformation in
order of 1-2 mm/yr in the 19-month period preceding the Northridge earthquake. By analyzing the coseismic and postseismic displacements at the JPLM and PVEP site locations, we infer (1) an increase in the contraction rate of the Los Angeles basin after the Landers earthquake, which is relieved by the Northridge earthquake; and (2) a possible role for the Landers earthquake in triggering the Northridge earthquake.

Citation
Bock, Y., van Domselaar, M., Fang, P., & Hudnut, K. W. (1998). Southern California Permanent GPS Geodetic Array: Continuous Measurements of Crustal Deformation in the Los Angeles Basin between the 1992 Landers and 1994 Northridge Earthquakes. Poster Presentation at Northridge Earthquake Research Conference.