GRACE and GRACE Follow-On Gravity Observations of Intermediate-Depth Earthquakes Contrasted With Those of Shallow Events

GRACE and GRACE Follow-On Gravity Observations of Intermediate-Depth Earthquakes Contrasted With Those of Shallow Events

Han, Shin-Chan (The University of Newcastle, Australia)
Sauber, Jeanne (NASA Goddard Space Flight Center)
Broerse, D.B.T. (TU Delft Physical and Space Geodesy)
Pollitz, Fred (U.S. Geological Survey)
Okal, Emile (Northwestern University)
Jeon, Taehwan (Seoul National University)
Seo, Ki Weon (Seoul National University)
Stanaway, Richard (Papua New Guinea University of Technology)

2024

Earthquakes involve mass redistribution within the solid Earth and the ocean, and as a result, perturb the Earth's gravitational field. For most of the shallow (<60 km) earthquakes with M_w > 8.0, the GRACE satellite gravity measurements suggest considerable volumetric disturbance of rocks. At a spatial scale of hundreds of km, the effect of volumetric change exceeds gravity change by vertical deformation; for example, negative gravity anomalies associated with volumetric expansion are characteristic patterns after shallow thrust events. In this study, however, we report contrasting observations of gravity change from two intermediate-depth (100–150 km) earthquakes of 2016 & 2017 Mw 8.0 (two combined) Papua New Guinea thrust faulting events and 2019 Mw 8.0 Peru normal faulting and highlight the importance of compressibility in earthquake deformation. The combined 2016/17 thrust events resulted in a positive gravity anomaly of 5–6 microGal around the epicenter, while the 2019 normal faulting produced a negative gravity anomaly of 3–4 microGal. Our modeling found that these gravity changes are manifestation of vertical deformation with limited volumetric change, distinct from gravity changes after the shallow earthquakes. The stronger resistance of rocks to volume change at intermediate-depth results in largely incompressible deformation and thus in a gravity change dominated by vertical deformation. In addition, malleable rocks under high pressure and temperature at depth facilitated substantial afterslip and/or fast viscoelastic relaxation causing additional vertical deformation and gravity change equivalent to the coseismic change. For the Papua New Guinea events, this means that postseismic relaxation enhanced coseismic uplift and relative sea level decrease.

deformation
earthquakes
GRACE
gravity change
viscoelastic relaxation

http://resolver.tudelft.nl/uuid:a1eefa48-1740-4350-a97c-f058a845885a

https://doi.org/10.1029/2023JB028362

2169-9313

JGR Solid Earth, 129 (2)

Institutional Repository

journal article

© 2024 Shin-Chan Han, Jeanne Sauber, D.B.T. Broerse, Fred Pollitz, Emile Okal, Taehwan Jeon, Ki Weon Seo, Richard Stanaway