Publications

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2016
Saunders, JK, Goldberg DE, Haase JS, Bock Y, Offield DG, Melgar D, Restrepo J, Fleischman RB, Nema A, Geng JH, Walls C, Mann D, Mattioli GS.  2016.  Seismogeodesy using GPS and low-cost MEMS accelerometers: Perspectives for earthquake early warning and rapid response. Bulletin of the Seismological Society of America. 106:2469-2489.   10.1785/0120160062   AbstractWebsite

The seismogeodetic method computes accurate displacement and velocity waveforms by optimally extracting high-frequency information from strong-motion accelerometers and low-frequency information from collocated Global Positioning System (GPS) instruments. These broadband observations retain the permanent (static) displacement, are immune to clipping and magnitude saturation for large earthquakes, and are sensitive enough to record P-wave arrivals. These characteristics make seismogeodesy suitable for real-time applications such as earthquake early warning. The Scripps Institution of Oceanography (SIO) has developed an inexpensive microelectromechanical systems (MEMS) accelerometer package to upgrade established GPS stations. We compare the performance of our MEMS accelerometer with an observatory-grade accelerometer using an experiment at the University of California San Diego Large High-Performance Outdoor Shake Table. We show that the two types of accelerometers agree in frequency ranges of seismological and engineering interest and produce equivalent seismogeodetic estimates of displacement and velocity. To date, 27 SIO MEMS packages have been installed at GPS monitoring stations in southern California and the San Francisco Bay area and have recorded four earthquakes (M4.2, M4.1, and two of M4.0). The P-wave arrivals are distinguishable in the seismogeodetic observations at distances of up to similar to 25 km away but not in the GPS-only displacements. There is no significant permanent deformation for these small events. This study demonstrates the lower limit of detectability and that seismogeodetic waveforms can also be a reliable early confirmation that an event is not large or hazardous. It also raises the possibility of rapid magnitude estimation through scaling relationships.

2013
Melgar, D, Crowell BW, Bock Y, Haase JS.  2013.  Rapid modeling of the 2011 Mw 9.0 Tohoku-oki earthquake with seismogeodesy. Geophysical Research Letters.   10.1002/grl.50590   AbstractWebsite

Rapid characterization of finite fault geometry and slip for large earthquakes is important for mitigation of seismic and tsunamigenic hazards. Saturation of near-source weak motion and problematic integration of strong-motion data into displacements make this difficult in real time. Combining GPS and accelerometer data to estimate seismogeodetic displacement waveforms overcomes these limitations by providing mm-level three-dimensional accuracy and improved estimation of coseismic deformation compared to GPS-only methods. We leverage collocated GPS and accelerometer data from the 2011 Mw 9.0 Tohoku-oki, Japan earthquake by replaying them in simulated real-time mode. Using a novel approach to account for fault finiteness, we generate an accurate centroid moment tensor solution independently of any constraint on the slab geometry followed by a finite fault slip model. The replay of GPS and seismic data demonstrates that robust models could have been made available within 3 min of earthquake initiation.