Rapid rupture directivity determination of moderate dip‐slip earthquakes with teleseismic body waves assuming reduced finite source approximation

Abstract For an earthquake with along‐dip rupture, there is opposite directivity effects on downgoing direct P wave and upgoing depth phases (pP and sP), and this can be exploited for resolving fault plane and rupture direction. We propose a method to calculate the reduced finite source synthetics for teleseismic P wave and determine the rupture directivity via waveform fitting. We verified the effectiveness of this method with forward tests and investigated its robustness against station selection, uncertainties in point source parameters, and uncertainties in source finiteness parameters. We applied this method to the 2011 Mw5.8 Virginia earthquake, the 2008 Mw6.0 Nevada earthquake, and six other dip‐slip earthquakes. For most cases, we obtained rupture directivity results consistent with previous studies, but the method could fail for along‐strike ruptures and very shallow earthquakes. Our method may help mitigate earthquake hazard by improving shake map with rapid rupture directivity analysis.