Crustal subsidence observed by GRACE after the 2013 Okhotsk deep-focus earthquake

• Published in: Geophysical research letters 2015-05, Vol.42 (9), p.3204-3209
• Main Authors: Tanaka, Yusaku, Heki, Kosuke, Matsuo, Koji, Shestakov, Nikolay V.
• Format: Article
• Language: English
• Subjects: 2013 Okhotsk deep-focus earthquake; Boundaries; Boundary layers; Climate; coseismic gravity change; crustal deformation; Deformation; Density; Depth; Detection; Earthquakes; Geophysics; GRACE; GRACE (experiment); Gravitation; Gravity; Ground motion; Marine; Moho; Recovering; Recovery; Remote sensing; Rock; Rocks; satellite geodesy; Satellites; Seismic activity; Seismic phenomena; Spaceborne remote sensing; Spatial discrimination; Spatial resolution; Subsidence; Thrust; Uplift
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL063838

Coseismic gravity changes stem from (1) vertical deformation of layer boundaries with density contrast (i.e., surface and Moho) and (2) density changes of rocks at depth. They have been observed in earthquakes with Mw exceeding ~8.5 by Gravity Recovery and Climate Experiment (GRACE) satellites, but those of M8 class earthquakes have never been detected clearly. Here we report coseismic gravity change of the 24 May 2013 Okhotsk deep earthquake (Mw8.3), smaller than the detection threshold. In shallow thrust faulting, factor (2) is dominant, while factor (1) remains secondary due to poor spatial resolution of GRACE. In the 2013 Okhotsk earthquake, however, factor (2) is insignificant because they occur at depth exceeding 600 km. On the other hand, factor (1) becomes dominant because the centers of uplift and subsidence are well separated and GRACE can resolve them. This enables GRACE to map vertical ground movements of deep earthquakes over both land and ocean. Key Points Gravity change of a M8 class earthquake was first detected by satellites Deep‐focus earthquakes change the gravity mainly by surface deformation GRACE can map 2‐D crustal deformation of deep‐focus earthquakes