In the 1970s, the Shumagin Islands region of the Alaska subduction zone was identified as a seismic gap expected to host a future great [moment magnitude ( ) ≥8.0] earthquake. More recent geodetic data indicate that this region is weakly coupled, and the geologic record shows little evidence of past large events. From July to October 2020, a series of earthquakes occurred in this region, raising the possibility of greater coupling. The initial 7.8 thrust faulting earthquake straddled the eastern edge of the Shumagin Gap and was followed by an 7.6 strike-slip earthquake within the Shumagin Gap. Stress modeling indicates that this strike-slip earthquake is in fact favored if the Shumagin Gap has low coupling, whereas a highly coupled Shumagin Gap inhibits that type and location of earthquake. The initial thrust earthquake and its afterslip enhanced the strike-slip loading within the subducting slab, helping to trigger the October event.
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| http://dx.doi.org/10.1126/sciadv.abf7590 | DOI Listing |
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Aseismic slip and recent ruptures of persistent asperities along the Alaska-Aleutian subduction zone.
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The frictional properties and slip behaviors of subduction thrusts play a key role in seismic and tsunami hazard assessment, especially in weakly coupled "seismic gaps". Here, we rely on GPS observations in the Shumagin Gap of the Aleutian subduction zone to derive the slip distribution of the 2020 Mw 7.8 Simeonof Island, Alaska earthquake and of the subsequent afterslip during the first 87-day period.
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Department of Geosciences, Pennsylvania State University, University Park, PA, USA.
In the 1970s, the Shumagin Islands region of the Alaska subduction zone was identified as a seismic gap expected to host a future great [moment magnitude ( ) ≥8.0] earthquake. More recent geodetic data indicate that this region is weakly coupled, and the geologic record shows little evidence of past large events.
View Article and Find Full Text PDFStrain accumulation during the 1980-85 interval has been measured by means of trilateration surveys in the Shumagin and Yakataga seismic gaps, which are the two regions identified as the most likely sites for the next great thrust earthquakes along the Alaska-Aleutian arc. No significant strain accumulation was detected in the Shumagin gap, but experience at similar subduction zones and simple models of the subduction process suggest that a measurable amount of strain should have accumulated. The most likely explanation of the observation is that subduction there is either aseismic or episodic.
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