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.

Resolving Differences in the Rupture Properties of M5 Earthquakes in California Using Bayesian Source Spectral Analysis

“…Note that our technique does not assume horizontal rupture, but instead solves for the rupture dip angle as a free parameter. However, a complete resolution of the rupture dip requires station coverage with a wide range of ray takeoff angles (Abercrombie, Poli, & Bannister, 2017; He & Ni, 2017; Park & Ishii, 2015), which is a condition that is rarely met for our data set. Because of this issue, uncertainties in dip direction are substantially larger than those for strike (where prior knowledge from moment tensor solutions provides additional constraints).…”

Directivity Modes of Earthquake Populations with Unsupervised Learning

“…Some studies have included other information, such as depth phases (e.g. He & Ni, 2017), to help constrain these cases, but in general it is a challenge common to all directivity analyses.…”

“…It should be understood that this results from a lack of sensitivity to along‐dip ruptures. Some studies have included other information, such as depth phases (e.g., He & Ni, ), to help constrain these cases, but in general, it is a challenge common to all directivity analyses.…”

Source Characteristics and Exacerbated Tsunami Hazard of the 2020 Mw 6.9 Samos Earthquake in Eastern Aegean Sea

“…On the other hand, the dipping direction remains unresolved from this method, which could be due to the similar dip angles of the two nodal planes as suggested in He and Ni (2017). With the constraint from near-field strong motion, Taymaz et al (2022) suggested a north-dipping model with updip and westward propagation of the bilateral rupture pattern could best fit teleseismic waveforms and well explain the aftershock distributions.…”

“…In addition, we adopted the reduced finite source method (He & Ni, 2017) to constrain the rupture directivity parameters. In this algorithm, teleseismic P waves are decomposed into down‐going waves (P and SP) and upgoing waves (pP and sP).…”