Long-Period Surface Motion of the Multi-Patch Mw9.0 Tohoku-Oki Earthquake

Abstract:

The GPS displacement time series are today mostly used for the estimation of the transient (period <2sec) and coseismic (static) displacement of an earthquake. In this study, we show that it is possible to capture the oscillatory ground motion (acceleration, velocity, displacement) induced by the Tohoku-Oki event for periods ranging from 3 to 100s by using GPS data processed in Precise Point Positioning (PPP) mode. We find that the ground motions of the sedimentary basins of Japan were large, corresponding to velocity and acceleration larger than 0.15m/s and 0.15m/s² , respectively, even for periods greater than 3s. We compare the GPS observables with a Ground Motion Prediction Equation (GMPE) designed for Japan seismicity and find that the Spectral Acceleration (SA) is well estimated for periods larger than 3s and distances ranging from 100 to 500km. Finally, through the analysis of the displacement attenuation plots for the examined period band, we show that the 2011 Tohoku-Oki event is likely composed of multiple rupture patches as suggested before by time-reversal inversions of seismic data.