Rapid Analysis of Changes after the Mw 8.2 Chignik earthquake from GRACE-Follow-On Intersatellite laser ranging measurements

Abstract

This poster introduces a new method of analyzing gravity change associated with the solid Earth deformation by earthquakes. The vertical deformation and density change after earthquakes result in changes in the Earth’s gravity field that are detectible by GRACE and GRACE Follow-On (GRACE-FO) spacecraft. Our approach exploits instantaneous gravity perturbation measured by the intersatellite ranging systems between two GRACE Follow-On satellites for early detection, with 1-3 days of latency after the event. This method can be particularly useful for assessing and distinguishing between early models of earthquake fault slip. The Mw 8.2 Chignik earthquake is near the coseismic detection threshold estimated during the earlier GRACE (2002-2017) and the current GRACE-FO (2018-present) gravity and mass change satellite missions. The GRACE-FO mass change data include the higher-precision Laser Ranging Interferometer in addition to the microwave (K-/Ka-band) instrument. A particular challenge for the Chignik event is that the Gulf of Alaska is poorly modeled with existing ocean correction models such as Atmosphere and Ocean De-aliasing (AOD) model currently used by the GRACE and GRACE-FO project. Two other subduction zone sequence of earthquakes of similar magnitude, the 2006-2007 Kuril events (Mw 8.3 & 8.1) and the 2009 Tonga-Samoa (Mw 8.1) complex event, exhibited large, long-wavelength post-seismic mass changes that were detectable by the GRACE and GRACE-FO data. Both cases produced on-going gravity changes that can be accounted for by viscoelastic relaxation. In fact, the cumulative gravity change over several years exceeded the coseismic gravity change. It is, therefore, anticipated that the Mw 8.2 Chignik event will likely yield significant postseismic gravity perturbation as well, depending primarily on the elastic lithosphere thickness and viscosity of the asthenosphere. Post-seismic relaxation following the earlier, nearby 2020 (M 7.8 & 7.6) earthquakes may contribute to the gravimetric signal as well. We will present our early results of gravity changes after the Mw 8.2 Chignik earthquake. Additionally, we will discuss what can be improved for timely detection of the gravity change signature and how we can use gravimetric data for a unique perspective on the subduction zone process.