The Capabilities of Seismogeodesy with Low-Cost MEMS Accelerometers and Very-High-Rate GNSS Data and Implications for Earthquake and Near-Shore Tsunami Early Warning

Abstract:

Studies of the number of fatalities for near-source coastal communities during the 2011 Mw 9.0 Tohoku-Oki earthquake and tsunami show that evacuation start time was a critical factor. The extent of the evacuation area was predetermined according to earthquake magnitude, which in this case was severely underestimated primarily due to magnitude saturation experienced with seismic data. Rapid magnitude-estimation schemes that utilize magnitude-scaling relationships based on maximum P-wave amplitude and peak ground displacement require accurate near-field displacements that are difficult to obtain with traditional strong-motion data alone because of baseline offsets at low frequencies. Here we describe a real time seismogeodetic approach that computes accurate near-field broadband displacements and velocities by combining collocated accelerometer data and high-rate GNSS displacement observations. The number of collocated stations currently operating in Western North America is insufficient for routine application of the method, especially for intermediate size events, and expansion is limited by the high cost of observatory-grade accelerometers. To ameliorate this, we have developed an inexpensive MEMS accelerometer package to upgrade established GNSS stations and an SIO Geodetic Module to transmit very-high-rate (10 Hz and greater) displacement and velocity waveforms via on-site precise point positioning. These packages have already been installed at 25 stations in California but have yet to experience a large event. We use experiments on the NEES@UCSD Large High-Performance Outdoor Shake Table to demonstrate the capabilities. We find that the seismogeodetic solutions using the MEMS and 10Hz GNSS data are comparable to those using observatory-grade accelerometers. We describe the expected performance of the MEMS seismogeodetic combination in the field based on these results and the benefits of such seismogeodetic data to earthquake and tsunami early warning.