Calibration of ElarmS using earthquakes in southern California

Louisa L.H. Tsang, Richard M. Allen and Gilead Wurman
University of California Berkeley

AGU Fall Meeting, San Francisco, December 2007.

We derive empirical magnitude scaling relationships for southern California using a dataset of 59 past earthquakes recorded in southern California by the Southern California Seismic Network (SCSN) between 1992 and 2003. The events range in magnitude from 3.0 to 7.3. We use the maximum predominant period (tau-p-max) and the peak displacement amplitude (Pd) measured from the first 4 seconds of P-wave arrivals to determine period-magnitude and amplitude-magnitude scaling relationships respectively. Our calibration study shows that the scaling relationships are similar to those derived for northern California. The average error in magnitude estimates is 0.2 magnitude units for events with magnitudes smaller than 4.5, 0.3 magnitude units for events with magnitudes ranging from 4.5 to 6.5, and 0.5 magnitude units for events with magnitudes greater than 6.5. All 59 events are processed offline by the ElarmS algorithms to generate the realtime AlertMap predictions of peak ground shaking. When the station density is high (as in the greater Los Angeles metropolitan region) the performance of ElarmS is good. In regions with lower station density the system becomes slower and the errors become larger. The AlertMap animations for these events will be available at the meeting.

© Richard M Allen