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Full-waveform Modeling Explains Surface-wave Diffraction Patterns Observed on Large Dense Seismic Networks

Description: 

Stripe-like patterns of amplitude and wavefront deviations of surface waves have been observed at large dense networks of broadband seismic stations such as USArray and, recently, AlpArray and AdriaArray. We have previously shown that the patterns are not caused by the structure beneath the observation location, but rather imported with the wavefield from outside the network footprint. We have confirmed the hypothesis that these patterns are caused by diffraction and interference after the wavefield has passed a strong scatterer. The wavefield carries the diffraction imprint for thousands of kilometers and allows for localizing the position of the scatterer, its size and strength. This previous explanation was based on modeling of the travel-time delays caused by the interference after passing a single scatterer.

The next step is confirming the viability of this explanation using full-waveform modeling in 3-D Earth structure. We utilize AxiSEM3D to simulate global wavefield propagation through 1) a simple case of a single scatterer, and 2) a more complex structure with several scatterers to compute teleseismic seismograms for hundreds of stations. We process the synthetics with the same methods as the real data, showing that the full-waveform modeling is capable of reproducing the interference patterns observed in real data. We demonstrate how the stripes emerge in synthetic amplitudes, group velocity deviations, wavefront distortion and arrival angle deviations, and how it affects the dispersion curve measurement. In addition, we also observe deviations elongated transversely to the direction of propagation in our model predictions. Such regions of apparently faster and slower velocities have also been observed in real data, but had no explanation until now. Our full-waveform modeling thus not only confirms our previous hypotheses but allows for new interpretations of the observed interference phenomena. Our findings have implications for surface-wave tomographic imaging of structure beneath the network and allow us to image distant anomalies that are causing diffraction far outside of the network footprint.

Session: Earth’s Structure from the Crust to the Core - III

Type: Oral

Date: 4/16/2025

Presentation Time: 02:00 PM (local time)

Presenting Author: Petr

Student Presenter: No

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