Integrated seismic source models: Spatiotemporal slip-rate and high-frequency radiation distributions of large earthquakes

Abstract:

The detailed and stable seismic source model of large earthquake is important to estimate strong ground motion and to calculate accurate tsunami waveforms as well as to understand the nature of earthquake. Slip-rate distributions of large earthquakes can be estimated by waveform inversions, which provide the broad features of the seismic source process. Since rapid acceleration and deceleration of a dynamic rupture generate high-frequency seismic waves, to comprehend fully the evolution of the rupture process during a large earthquake, it is necessary to construct a spatiotemporal slip-rate distribution that can explain the high-frequency components. However, it is difficult to estimate the slip-rate distribution including the high-frequency components by waveform inversion because of the uncertainty of the Green’s functions.

Recently, the back-projection (BP) method has been widely used to estimate the spatiotemporal distribution of the high-frequency radiation source. The clear advantage of BP is that it makes possible to obtain the high-frequency radiation without the theoretical Green’s functions. However, the timing of the sub-events estimated by the BP methods can be distorted by the effects of reflected phases (e.g., pP and sP phases), As a result, it is quite difficult to reliably compare the distribution of sub-events obtained by BP and the spatiotemporal slip-rate distributions inferred by waveform inversion. The Hybrid BP (HBP) method was developed to avoid the distortion effects of reflected phases. The HBP method uses the Green’s functions to mitigate the effect of reflected phases, and the HBP result can thus be compared to the slip-rate distribution obtained by the waveform inversion.

 In this study, we used the newly developed inversion and HBP methods to estimate the slip-rate distribution and high-frequency radiation (around 1 Hz) related to rapid acceleration and deceleration of a dynamic rupture, respectively, of recent large earthquake from teleseismic P-wave data. We compared the high-frequency radiation event and the slip-rate distribution, and then constructed an integrated source model that we are able to use to infer the detailed dynamic rupture process during large earthquakes.