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Rupture directivities of 70 M 3.5-5.5 Ridgecrest earthquakes obtained from energy envelope deconvolution

Zhe Jia, Peter M. Shearer, & Wenyuan Fan

Submitted September 10, 2023, SCEC Contribution #13108, 2023 SCEC Annual Meeting Poster #032

Earthquake rupture directivity characterizes rupture propagation and impacts ground motion. This source property can be used to infer rupture dynamics and fault zone properties, having important implications in earthquake physics. However, rupture directivity is challenging to measure, which requires an even azimuthal coverage of seismic stations for a robust analysis. For small to moderate size earthquakes, rupture directivity estimation is particularly challenging due to their compact rupture sizes. Here, we develop a novel deconvolution approach that uses energy envelopes of S coda waves to remove path effects and extract rupture characteristics. Our method is similar to the commonly used empirical Green's Function (EGF) method in which we use smaller co-located events to remove the path effects for larger target earthquakes. However, our method benefits from better coherency of energy envelopes at high frequencies, which often cause cycle-skipping issues in the conventional waveform deconvolution. We validate our energy deconvolution analysis using well-studied moderate size events and apply the algorithm to determine rupture directivities of 70 Magnitude (M) >3.5 aftershocks in the 2019 Ridgecrest earthquake sequence. Their rupture directivities agree with the orthogonal interlocking fault branches inferred from relocated aftershock catalogs, but the ruptures do not show a preference for a single orientation, which may suggest insignificant bimaterial effect yet heterogeneous fault properties within an immature fault system. Our approach enables directivity measurements at lower magnitudes than most existing methods and has great potential for mapping fault structures in high resolution.

Jia, Z., Shearer, P. M., & Fan, W. (2023, 09). Rupture directivities of 70 M 3.5-5.5 Ridgecrest earthquakes obtained from energy envelope deconvolution. Poster Presentation at 2023 SCEC Annual Meeting.

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