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.