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Testing Models of Active Tectonics in the Central Walker Lane Using Satellite Geodetic Measurement of the Mw 6.5 Monte Cristo Range Earthquake

Session: Intermountain West Earthquakes in the Spring of 2020 II

Type: Oral

Date: 4/20/2021

Presentation Time: 06:30 PM Pacific

Description: 

The Monte Cristo Range Mw 6.5 earthquake occurred in the eastern central Walker Lane on May 15^th, 2020. While the moment tensor shows a left lateral strike slip solution, geodetic data reveal subsidence to the west of the epicenter, possibly indicating a normal component of slip. The presence of normal slip is potentially important because it may be diagnostic of extension dominated transtension, whereas purely left-lateral slip is more consistent with wrench-style block rotations. Thus, if the normal component slip contributed significantly to the earthquake it has important implications for tectonic models of the region.

We address this question by investigating the rupture process of the earthquake using satellite geodesy, namely GPS and InSAR. Three-component coseismic surface motions due to the event are measured at over 200 GPS stations within 280 km of the epicenter. InSAR resolves coseismic motion in two descending plus one ascending line of sight (LOS). We use displacement data as input to a joint inversion for the best fit fault locations and slip distribution using forward and inverse modeling and global search optimization. The inversion method uses equations from Okada 1985, which are calculated in three components at each GPS location, and projected to LOS at each InSAR location. While the InSAR is most sensitive to east and vertical components, and least sensitive in the north component, the closest GPS station to the epicenter (COLU) shows north displacement greater than the east and vertical. Our method does not assume that the InSAR signal is the result of only east-west and up-down movement, and constrains the north component movement with GPS observations.

Initial results indicate a normal component of slip on the western side of the preferred fault. The contribution of this slip to the total moment, its relationship to surface rupture, and implications for tectonic models will be explored with refinement of the joint inversion.

Presenting Author: Aren T. Crandall-Bear

Student Presenter: Yes

Authors