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Abstract Elevated seismic noise for moderate‐size earthquakes recorded at teleseismic distances has limited our ability to see their complexity. We develop a machine‐learning‐based algorithm to separate noise and earthquake signals that overlap in frequency. The multi‐task encoder‐decoder model is built around a kernel pre‐trained on local (e.g., short distances) earthquake data (Yin et al., 2022,https://doi.org/10.1093/gji/ggac290) and is modified by continued learning with high‐quality teleseismic data. We denoise teleseismic P waves of deep Mw5.0+ earthquakes and use the clean P waves to estimate source characteristics with reduced uncertainties of these understudied earthquakes. We find a scaling of moment and duration to beM0 ≃ τ4, and a resulting strong scaling of stress drop and radiated energy with magnitude ( and ). The median radiation efficiency is 5%, a low value compared to crustal earthquakes. Overall, we show that deep earthquakes have weak rupture directivity and few subevents, suggesting a simple model of a circular crack with radial rupture propagation is appropriate. When accounting for their respective scaling with earthquake size, we find no systematic depth variations of duration, stress drop, or radiated energy within the 100–700 km depth range. Our study supports the findings of Poli and Prieto (2016,https://doi.org/10.1002/2016jb013521) with a doubled amount of earthquakes investigated and with earthquakes of lower magnitudes.
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Stress Drop Variation of Deep‐Focus Earthquakes Based on Empirical Green's Functions
Abstract We analyze source characteristics of global, deep‐focus (>350 km) earthquakes with moment magnitudes (Mw) larger than 6.0–8.2 using teleseismic P‐wave and S‐wave spectra and an empirical Green's functions approach. We estimate the corner frequency assuming Brune's source model and calculate stress drops assuming a circular crack model. Based on P‐wave and S‐wave spectra, the one standard deviation ranges are 3.5–369.8 and 8.2–328.9 MPa, respectively. Based on the P‐wave analysis, the median of our stress drop estimates is about a factor of 10 higher than the median stress drop of shallow earthquakes with the same magnitude estimated by Allmann and Shearer (2009,https://doi.org/10.1029/2008JB005821). This suggests that, on average, the shear stress of deep faults in the mantle transition zone is an order of magnitude higher than the shear stress of faults in the crust. The wide range of stress drops implies coexistence of multiple physical mechanisms.
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- Award ID(s):
- 2019379
- PAR ID:
- 10376561
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 47
- Issue:
- 9
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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