Empirical Laws of Location and Rupture Time of Asperities for Strong Ground Motion Prediction

Abstract

The location of asperities on a fault plane, together with rupture times, has a significant influence on strong ground motion. If these positions for predicting strong ground motions of future earthquakes could be set empirically based on data from actual earthquakes, it would be possible to predict ground motions with better accuracy and greater adherence to reality. For some earthquakes, data and dynamic rupture simulations have shown that the time from the beginning of the seismic waveform until the amplitude increases scales with the earthquake magnitude. In this study, the author extracted asperities from fault slip data inferred by waveform inversion and showed that asperity rupture times and distances between asperities (or maximum slip subfault)and hypocenters are proportional to the cube root of the seismic moment. It was also confirmed that this relationship is not merely attributed to an increase in fault area with the increase in magnitude of the earthquake. Scaling laws were also obtained for each earthquake type (inland, inter-plate, and intra-plate) and focal mechanism. The distance from the hypocenter to the asperities (or maximum slip subfault) is the greatest for the strike-slip and inland earthquakes. Furthermore, in 71.1% of the strike-slip earthquakes and 71.8% of the inland earthquakes, the maximum slip point was found to be located shallower than the hypocenter. In addition, 70.5% of the asperities closest to the hypocenter are the largest asperities on the fault plane. The percentages of maximum slip points located at the asperities closest to the hypocenter and at the largest asperity on the fault plane are 73.5% and 86.8%, respectively. The empirical rules presented in this study are useful for improving the accuracy of prediction results by setting the location of asperities and rupture times in the models used for strong ground motion prediction to match those of actual earthquakes.