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A new seismogeodetic approach applied to GPS and accelerometer observations of the 2012 Brawley seismic swarm: Implications for earthquake early warning

Jianghui Geng, Yehuda Bock, Diego Melgar, Brendan W. Crowell, & Jennifer S. Haase

Published July 2013, SCEC Contribution #1732

The 26 August 2012 Brawley seismic swarm of hundreds of events ranging from M1.4 to M5.5 in the Salton trough, California provides a unique data set to investigate a new seismogeodetic approach that combines Global Positioning System (GPS) and accelerometer observations to estimate displacement and velocity waveforms in real time. First, we analyzed 1-5 Hz GPS data collected by 17 stations, fully encircling the swarm zone from near-field distances to about 40 km, using the novel approach of precise point positioning with ambiguity resolution (PPP-AR). We used a reference network of North American GPS stations to estimate fractional-cycle biases and satellite clock parameters, which were then combined with ultra-rapid orbits from the International GNSS Service and the PPP-AR methodology to estimate positions during the Brawley seismic swarm. Next, we performed a seismogeodetic analysis of the GPS data and 100-200 Hz accelerometer data collected at three collocated stations, using a new tightly-coupled Kalman filter approach integrated with the PPP-AR process. We can clearly discern body waves in the velocity waveforms, including P-wave arrivals not detectable with the GPS-only approach for earthquake magnitudes as low as Mw 4.6. We reproduce the full spectrum of broadband motions including the static component for magnitudes as low as Mw5.4. Our study shows that GPS networks upgraded with strong motion accelerometers can effectively provide in real time alerts for any earthquake of societal significance and can be of critical value in creating a robust early warning system.

Citation
Geng, J., Bock, Y., Melgar, D., Crowell, B. W., & Haase, J. S. (2013). A new seismogeodetic approach applied to GPS and accelerometer observations of the 2012 Brawley seismic swarm: Implications for earthquake early warning. Geochemistry, Geophysics, Geosystems, 14(7), 2124-2142. doi: 10.1002/ggge.20144.