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Earthquake Source Complexity Controls the Frequency-Dependence of Near-Source Radiation Patterns
  • Daniel T. Trugman,
  • Shanna X Chu,
  • Victor Chen Tsai
Daniel T. Trugman
The University of Texas at Austin

Corresponding Author:[email protected]

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Shanna X Chu
Brown University
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Victor Chen Tsai
Brown University
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The spatial patterns of earthquake ground motion amplitudes are commonly represented using a double couple model that corresponds to shear slip on a planar fault. While this framework has proven successful in explaining low-frequency seismic recordings, at higher frequencies the wavefield becomes more azimuthally isotropic for reasons that are not yet well understood. Here we use a dense array of nodal seismometers in Oklahoma to study the radiation patterns of earthquakes in the near-source region where wavefield scattering effects are limited. At these close distances, the radiation pattern is predominantly double couple at low frequencies (<15Hz). At higher frequencies, the recorded wavefield contains significant isotropic and residual components that cannot be explained as path or site effects, implying complexity in the rupture process or local fault zone structure. These findings demonstrate that earthquake source complexity can drive variability in the ground motions that control seismic hazard.
08 Sep 2021Published in Geophysical Research Letters volume 48 issue 17. 10.1029/2021GL095022