Seismic Velocity Changes in the Backarc Continental Crust After the 2011 Mw 9.0 Tohoku‐Oki Megathrust Earthquake

• Published in: Geophysical research letters 2017-11, Vol.44 (21), p.10,997-11,003
• Main Authors: Hong, Tae‐Kyung, Lee, Junhyung, Chi, Donggeun, Park, Seongjun
• Format: Article
• Language: English
• Subjects: backarc crust; Continental crust; Earthquakes; Korean Peninsula; medium perturbation; megathrust earthquake; Rayleigh waves; Seismic activity; Seismic velocities; seismic velocity; Seismic waves; Shear wave velocities; Travel time; Velocity; Wave velocity; Waveforms
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL075447

The 2011 Mw 9.0 Tohoku‐Oki megathrust earthquake accompanied coseismic and postseismic displacements around the eastern Eurasian continental plate. Noise cross correlations produced transient seismic waveforms along interstation paths in the Korean Peninsula. We measured the traveltime changes of the fundamental mode Rayleigh waves over the range of 0.03–0.08 Hz after the megathrust earthquake. The temporal seismic velocity changes in the lower crust were assessed from the traveltime changes. The traveltimes increased instantly after the megathrust earthquake and were gradually recovered over several hundreds to thousands of days. The instant shear wave velocity decreases ranged between 0.731 (±0.057)% and 4.068 (±0.173)%. The temporal medium perturbation might be caused by the transient uniaxial tensional stress due to the coseismic and postseismic displacements. The medium properties may be recovered by progressive stress field reconstruction. Key Points The regional backarc crust experiences instant seismic velocity changes after a megathrust earthquake The perturbed seismic velocities are recovered gradually with time The seismic velocity changes are strong along the great‐circle directions to the event epicenter