Abstract
Although moderate‐size earthquakes are poorly studied by lack of near‐fault observations, they can provide key information about larger damaging earthquakes. Here we propose a new approach, inspired by double‐difference relocation, 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, 5.2 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 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 be useful in better understanding the preparation phase and rupture of both tectonic and induced earthquakes.
Highlights
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 ∼2.8 km/s, highlighting two main rupture events imaged by InSAR
We present a new data-driven method, called seismic stereometry, to estimate finite fault rupture parameters for intermediate-size earthquakes, which does not rely on inversion nor deconvolution by an empirical or synthetic Green's function
Seismic stereometry can be seen as a generalization of earthquake location by double-difference methods (Waldhauser & Ellsworth, 2000) applied to the different high-frequency pulses generated during an earthquake source
Summary
Questions such as what drives small rupture instability (Campillo & Ionescu, 1997; Dieterich, 1979; Latour et al, 2013; Rubin & Ampuero, 2005) to grow seemingly to either small or large earthquakes, or what a fault rupture history can tell about its potential to generate a large earthquake (Bouchon et al, 2011, 2013; Ellsworth & Bulut, 2018; Ruiz et al, 2017; Tape et al, 2018; Yoon et al, 2019), are still largely debated in seismology (Ellsworth & Beroza, 1995; Beroza & Ellsworth, 1996; Mori & Kanamori, 1996; Mignan, 2014; Olson & Allen, 2005). Assessing these attributes accurately for small-to-intermediate earthquakes is of paramount importance to constrain fundamental earthquake physics and scaling laws across all magnitude ranges, such as the approximately constant stress-drop for all earthquake sizes (Aki, 1967; Shaw, 2009). The uncertainties on the structure or the small event induce uncertainties on the source parameters of the mainshock (Mai et al, 2016) Another way to estimate some finite fault earthquake source properties is by using a dense seismic network with the back-projection technique which maps the spatiotemporal distribution of high-frequency radiations along the fault Because of the targeted earthquake size, we believe that seismic stereometry can have a strong potential to study, among others, induced seismicity generated by resource production and help mitigate the associated seismic risk
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