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Journal Articles Journal of Geophysical Research : Solid Earth Year : 2022

Seismic Waveform-Coherence Controlled by Earthquake Source Dimensions

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Tong Zhou
  • Function : Author
Lingsen Meng
  • Function : Author
Ailin Zhang
  • Function : Author
Jean Paul Ampuero

Abstract

Rupture size is a fundamental earthquake source parameter that is challenging to infer independently from far-field seismological observations. Here, we develop a novel observational constraint on source size based on the decay rate of wavefield coherence across a seismic array. For a given earthquake, waveform coherence decays with increasing interstation distance or, more precisely, with increasing projection difference defined as the difference between the takeoff vectors associated to the two stations projected along the rupture direction. We find that coherence generally falls off with projection difference faster for earthquakes of larger magnitudes. The magnitude dependence of the coherence decay rate can be explained by a finite source effect: larger source sizes cause larger differences of phase delays between waves arriving from different parts of the rupture at different stations, hence a stronger spatial variability of the wavefield, resulting in a breakdown of waveform coherence. Assuming a 1-D Haskell's source model, the rupture size can be estimated from the coherence decay rate. We apply this method to USArray data of earthquakes in three subduction zones, the Sea of Okhotsk, South America and Japan. The source sizes inferred from the coherence decay patterns are consistent with scaling relations intermediate between width-saturated L-models and quasi equi-dimensional rupture models. Our observation captures a unique pattern of array waveform coherence and demonstrates the potential of utilizing waveform coherence to study earthquake source parameters.
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Dates and versions

insu-03688501 , version 1 (04-06-2022)

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Tong Zhou, Lingsen Meng, Ailin Zhang, Jean Paul Ampuero. Seismic Waveform-Coherence Controlled by Earthquake Source Dimensions. Journal of Geophysical Research : Solid Earth, 2022, 127 (5), pp.e2021JB023458. ⟨10.1029/2021JB023458⟩. ⟨insu-03688501⟩
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