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S Coda and Rayleigh Waves From a Decade of Repeating Earthquakes Reveal Discordant Temporal Velocity Changes Since the 2004 Sumatra Earthquake
Author(s) -
Yu W.,
Lin J.T.,
Su J.,
Song T.R. A.,
Kang C.C.
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2020jb019794
Subject(s) - coda , seismology , geology , rayleigh wave , slow earthquake , surface wave , seismic wave , microseism , geophysics , ground motion , peak ground acceleration , interplate earthquake , physics , astronomy
Temporal changes in the subsurface seismic velocity structure reflect the physical processes that modulate the properties of the media through which seismic waves propagate. These processes, such as healing of the surface damage zone and deep crustal deformation, are described by similar functional forms and operate on similar timescales, making it difficult to determine which process drives the observed changes. We examine earthquake‐induced velocity changes using the measured lag‐time time series τ ( t ) of the repeating earthquake sequences since the 2004 M w 9.2 Sumatra and 2005 M w 8.6 Nias earthquakes. The S coda velocity changes ( δV S , equivalent to −τ S ) recover steadily during the 2005–2015 period. The Rayleigh wave velocity changes ( δV LR , or −τ LR ) undergo transient recovery, followed by a strong δV LR reduction in late 2007. δV S recovery is most likely driven by deep processes, whereas the temporal breaks in δV LR recovery in 2007 mostly reflect surface damage and healing induced by the strong ground motions of the 2004 M w 9.2, 2005 M w 8.6, 2007 M w 8.4, and M w 7.9 Bengkulu and 2008 M w 7.3 Simeulue earthquakes. The observed differences between the temporal variations in δV S and δV LR can distinguish deep processes from healing of the surface damage zone.