Integration of GNSS and Seismic Data for Earthquake Early Warning: A Case Study on the 2011 Mw 9.0 Tohoku-Oki Earthquake

摘要

Earthquake early warning (EEW), which is considered to be a pragmatic and viable way to reduce the damage and casualties during a large earthquake, relies on the accurate estimation of broadband displacements and the capability of rapidly detection of the first arrival wave (P-wave). Real-time high-rate GNSS is a reliable tool to directly capture displacements including static offsets and dynamic motions at the near field, which does not suffer from the clip, rotation and tilt problems as the traditional seismic instrument does. However, due to the large high-frequency noise and the low sampling rates of GNSS measurements, it is hard to pick up the P-wave arrival accurately in GNSS-derived displacement history. To overcome this problem, the combination of high-rate GNSS and collocated accelerometers shows promise as a more reliable and effective way, because accelerometers perform very well with high precision in the high-frequency range. In this study, we investigate the method by using collocated GNSS and accelerometers for EEW. We first introduce a new approach, namely the temporal point positioning (TPP) method, which could directly obtain coseismic displacement with a single GNSS receiver in real-time. The TPP method overcome the convergence problem of precise point positioning (PPP), and also avoids the integration process of the Variometric approach. And then we apply a multi-rate Kalman filter to fuse GNSS-derived coseismic displacement with collocated accelerometer data for attaining integrated displacements with a high precision and reliability. Finally, we detect the arrival time of P-wave and determine the earthquake magnitude from the integrated results. The performance of collocated GNSS and accelerometers is validated using data from GEONET (1 Hz GPS) and K-NET/KiK-Net (100 Hz accelerometer) stations, with the collocated distance less than 2 km, in the near field of the Mw 9.0 Tohoku-Oki earthquake occurred on March 11, 2011. Using the broadband displacements derived by the above method, we detect the arrival time of P-wave with a mean value 0.15 s offset different from the USGS reference values, and the estimated magnitude is Mw 9.06, which is achievable within 2-3 min after earthquake initiation.