Postseismic Deformation Following the July 2020 Simeonof Earthquake
Session: The 2020 Simeonof Island, Alaska, Earthquake: Observations, Modeling and Tectonic Insights
Type: Oral
Date: 4/21/2021
Presentation Time: 05:30 PM Pacific
Description:
The July 2020 Simeonof earthquake was followed by substantial postseismic deformation. Over the four months between the mainshock and the November M7.6 aftershock, the cumulative postseismic displacements at sites near the rupture amounted to 25-50% of the coseismic displacements, but with a very different spatial pattern. Both the orientations of the postseismic displacement vectors and the ratio of vertical to horizontal displacement are clearly distinct from those of the coseismic displacements. The postseismic horizontal displacements from the three sites closest to the rupture are very close to a trench-normal orientation, while the coseismic displacements at two of those sites were rotated counter-clockwise from trench-normal. Postseismic vertical displacements were smaller overall than the coseismic vertical displacements. Together, these indicate that the postseismic afterslip has a different spatial distribution than the coseismic slip, and/or that viscoelastic relaxation plays a substantial role in the postseismic deformation.
We will test kinematic and stress-driven afterslip models as well as viscoelastic relaxation models to explain the postseismic deformation. Given the location of the coseismic rupture, which did not rupture the shallow part of the subduction interface, it is possible that afterslip could occur either updip or downdip of the coseismic rupture. The presence or absence of updip afterslip is particularly important for analysis of the overall slip budget for the interface. We will test alternative afterslip models with different constraints on the potential location of afterslip to evaluate how well the GPS (and potential InSAR) data constrain the postseismic slip pattern.
Presenting Author: Jeffrey T. Freymueller
Student Presenter: No
Authors
Jeffrey Freymueller Presenting Author Corresponding Author freymuel@msu.edu Michigan State University |
Julie Elliott julieelliott@purdue.edu Purdue University |
Ronni Grapenthin rgrapenthin@alaska.edu University of Alaska Fairbanks |
Zhuohui Xiao zhhxiaomsu@gmail.com Michigan State University |
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Postseismic Deformation Following the July 2020 Simeonof Earthquake
Category
The 2020 Simeonof Island, Alaska, Earthquake: Observations, Modeling and Tectonic Insights