From California to British Columbia, the Pacific Northwest coast bears an omnipresent earthquake and tsunami hazard from the Cascadia subduction zone. Multiple lines of evidence suggests that magnitude eight and greater megathrust earthquakes have occurred ‐ the most recent being 321 years ago (i.e., 1700 A.D.). Outstanding questions for the next great megathrust event include where it will initiate, what conditions are favorable for rupture to span the convergent margin, and how much slip may be expected. We develop the first 3‐D fully dynamic rupture simulations for the Cascadia subduction zone that are driven by fault stress, strength and friction to address these questions. The initial dynamic stress drop distribution in our simulations is constrained by geodetic coupling models, with segment locations taken from geologic analyses. We document the sensitivity of nucleation location and stress drop to the final seismic moment and coseismic subsidence amplitudes. We find that the final earthquake size strongly depends on the amount of slip deficit in the central Cascadia region, which is inferred to be creeping interseismically, for a given initiation location in southern or northern Cascadia. Several simulations are also presented here that can closely approximate recorded coastal subsidence from the 1700 A.D. event without invoking localized high‐stress asperities along the down‐dip locked region of the megathrust. These results can be used to inform earthquake and tsunami hazards for not only Cascadia, but other subduction zones that have limited seismic observations but a wealth of geodetic inference.
- Award ID(s):
- 1802364
- NSF-PAR ID:
- 10412025
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 51
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract On 29 July 2021, an
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Abstract Shallow slow-slip events (SSEs) contribute to strain release near the shallow portions of subduction interfaces and may contribute to promoting shallow subduction earthquakes. Recent efforts in offshore monitoring of shallow SSEs have provided evidence of possible interactions between shallow SSEs and megathrust earthquakes. In this study, we use a dynamic earthquake simulator that captures both quasi-static (for SSEs) and dynamic (for megathrust earthquakes) slip to explore their interactions and implications for seismic and tsunami hazards. We model slip behaviors of a shallow-dipping subduction interface on which two locally locked patches (asperities) with different strengths are embedded within a conditionally stable zone. We find that both SSEs and earthquakes can occur, and they interact over multiple earthquake cycles in the model. Dynamic ruptures can nucleate on the asperities and propagate into the surrounding conditionally stable zone at slow speeds, generating tsunami earthquakes. A clear correlation emerges between the size of an earthquake and SSE activities preceding it. Small earthquakes rupture only the low-strength asperity, whereas large earthquakes rupture both. Before a large earthquake, periodic SSEs occur around the high-strength asperity, gradually loading stress into its interior. The critically stressed high-strength asperity can be ruptured together with the low-strength one in the large earthquake, followed by a relatively quiet interseismic period with very few SSEs and then a small earthquake. An SSE may or may not directly lead to nucleation of an earthquake, depending on whether a nearby asperity is ready for spontaneously dynamic failure. In addition, because of different SSE activities, the coupling degree may change dramatically between different interseismic periods, suggesting that its estimate based on a short period of observation may be biased.more » « less
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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 2014
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2216843119
