Seismic Stereometry reveals preparatory behavior and source kinematics of intermediate-size earthquakes

Abstract:

Although moderate-size earthquakes are poorly studied due to a lack of near-fault observations, they can provide critical information about larger damaging earthquakes. Here we propose a new approach, inspired by double-difference relocation and based on stereoscopic effects produced at two stations by the propagating rupture, that uses high coherency waveforms recorded at neighboring sensors to study the preparation phase and dynamics of moderate-size earthquakes. We validate this technique by analyzing the 2016, Mw5.2 Borrego Springs earthquake in Southern California, and find consistent rupture velocities of 2 km/s highlighting two main rupture asperities. The analysis of the 2019, Ml5.2 Le Teil earthquake in France reveals slow nucleation at depth that migrates to the surface and propagates Northward with a velocity of $\sim$2.8 km/s, highlighting two main rupture events also imaged by InSAR. By providing unprecedented resolution in our observation of the rupture dynamics, this approach will find it useful to understand better the preparation phase and rupture of both tectonic and induced earthquakes.