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Abstract Slow slip events (SSEs) have been observed in spatial and temporal proximity to megathrust earthquakes in various subduction zones, including the 2014Mw7.3 Guerrero, Mexico earthquake which was preceded by aMw7.6 SSE. However, the underlying physics connecting SSEs to earthquakes remains elusive. Here, we link 3D slow‐slip cycle models with dynamic rupture simulations across the geometrically complex flat‐slab Cocos plate boundary. Our physics‐based models reproduce key regional geodetic and teleseismic fault slip observations on timescales from decades to seconds. We find that accelerating SSE fronts transiently increase shear stress at the down‐dip end of the seismogenic zone, modulated by the complex geometry beneath the Guerrero segment. The shear stresses cast by the migrating fronts of the 2014Mw7.6 SSE are significantly larger than those during the three previous episodic SSEs that occurred along the same portion of the megathrust. We show that the SSE transient stresses are large enough to nucleate earthquake dynamic rupture and affect rupture dynamics. However, additional frictional asperities in the seismogenic part of the megathrust are required to explain the observed complexities in the coseismic energy release and static surface displacements of the Guerrero earthquake. We conclude that it is crucial to jointly analyze the long‐ and short‐term interactions and complexities of SSEs and megathrust earthquakes across several (a)seismic cycles accounting for megathrust geometry. Our study has important implications for identifying earthquake precursors and understanding the link between transient and sudden megathrust faulting processes.
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The Earth's Surface Controls the Depth‐Dependent Seismic Radiation of Megathrust Earthquakes
Abstract Megathrust earthquakes exhibit a ubiquitous seismic radiation style: low‐frequency (LF) seismic energy is efficiently emitted from the shallowest portion of the fault, whereas high‐frequency (HF) seismic energy is efficiently emitted from the deepest part of the fault. Although this is observed in many case‐specific studies, we show that it is ubiquitous in global megathrust earthquakes between 1995 and 2021. Previous studies have interpreted this as an effect of systematic depth variation in either the plate interface frictional properties (Lay et al., 2012) or the P wavespeeds (Sallarès & Ranero, 2019). This work suggests an alternative hypothesis: the interaction between waves and ruptures due to the Earth's free surface is the leading mechanism that generates this behavior. Two‐dimensional dynamic rupture simulations of subduction zone earthquakes support this hypothesis. Our simulations show that the interaction between the seismic waves reflected at the Earth's free surface and the updip propagating rupture results in LF radiation at the source. In contrast, the downdip propagation of rupture is less affected by the free surface and is thus dominated by HF radiation typical of buried faults. To a second degree, the presence of a realistic Earth structure derived from P‐wave velocity (VP) tomographic images and realistic VP/VSratio estimated in boreholes further enhances the contrast in source radiation. We conclude that the Earth's free surface is necessary to explain the observed megathrust earthquake radiation style, and the realistic structure of subduction zone is necessary to better predict earthquake ground motion and tsunami potential.
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- Award ID(s):
- 2124722
- PAR ID:
- 10368131
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- AGU Advances
- Volume:
- 2
- Issue:
- 3
- ISSN:
- 2576-604X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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