ElarmS Earthquake Alarm Systems: Early Results in Northern California

Gilead Wurman and Richard M. Allen
University of California Berkeley

1906 Earthquake Conference/SSA April 2006

Earthquake Alarm Systems (ElarmS) is a program for earthquake early warning which uses measurement of P-wave predominant period to predict the magnitude of an earthquake in progress within the first four seconds of the Pwave arrival. ElarmS has potential applications in areas where seismically hazardous faults exist in close proximity to densely populated areas. In such areas, the use of the P-wave to assess hazard provides valuable additional seconds over more traditional frontal detection methods which make use of maximum ground shaking observations. ElarmS has been tested in an offline setting in Southern California.

We present early results of the application of ElarmS in Northern California generally and the San Francisco Bay Area particularly. The initial calibration of ElarmS for Northern California is complete. As of January 2006, ElarmS will be operating automatically at the Berkeley Seismological Laboratory but processing will be delayed by 10 to 15 minutes. This implementation simulates actual real-time processing, but the results do not realistically model telemetry problems or delays. The execution of the code is initiated by the receipt of an advisory e-mail from the Northern California Earthquake Data Center and delayed by ten minutes to allow for sufficient data to be logged for the processing to occur at one time after all the data are available. This is in contrast to future real-time processing which would occur while the data is being logged. Each event is also reprocessed one week after it has occurred, in order to evaluate the effect of data drop-out on the results.

The code is executed after all M > 3 events recorded by the NCEDC. The performance of ElarmS is presented in terms of predicted vs. actual magnitude, predicted vs. observed peak ground motions and warning time to peak ground motion in urban areas.