A Study of Ground Motion Excitation Based on the Earthquake of September 8, 2017: Evidence that Normal Faults Influence the Stress Parameter

Abstract

We performed a study of ground motion modeling based on multiple linear regression and random vibration theory using the earthquake sequence of September 8, 2017 (Mw = 8.2). Our results show that there is high attenuation in the region of Oaxaca–Chiapas and central Mexico; however, the peak amplitude excitations of normal fault earthquakes are higher than those of thrust fault earthquakes. The earthquake sequence involved a large number of events, but not all the seismic events were aftershocks because many earthquakes had different rupture styles. The thrust events follow a simple scaling relation with a constant stress parameter, but the normal fault events are difficult to represent with a constant self-similar model. Our best result consists of a $$Q_{0} = 240 \pm 032$$ with a frequency-dependent factor of $$0.63 \pm 0.05$$ . The excitation term is well determined with a stress parameter of 80 bars for the thrust faults, but for the normal faults, the stress parameter is at least 180 bars with a non-self-similar model. Our results show that it is necessary to include new ground motion prediction equations in seismic hazard analysis for “meganormal” faults, which have not previously been considered in subduction zones.