Matthew W Herman1, Kevin P Furlong2. 1. Department of Geological Sciences, California State University, Bakersfield, Bakersfield, CA, USA. mherman2@csub.edu. 2. Department of Geosciences, Pennsylvania State University, University Park, PA, USA.
Abstract
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 (M w) ≥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 M w 7.8 thrust faulting earthquake straddled the eastern edge of the Shumagin Gap and was followed by an M w 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.
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 (M w) ≥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 M w 7.8 thrust faulting earthquake straddled the eastern edge of the Shumagin Gap and was followed by an M w 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.
Authors: Gavin P Hayes; Ginevra L Moore; Daniel E Portner; Mike Hearne; Hanna Flamme; Maria Furtney; Gregory M Smoczyk Journal: Science Date: 2018-08-09 Impact factor: 47.728