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TitleA model of shallow viscoelastic relaxation for seismically induced tension cracks in the Chile-Peru forearc
AuthorLuo, H; Wang, KORCID logo; Sone, H; He, J
SourceGeophysical Research Letters vol. 46, issue 19, 2019 p. 10773-10781, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190305
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf; html
ProvinceOffshore region
AreaChile; Peru
Lat/Long WENS -73.5000 -69.0000 -18.0000 -24.0000
Subjectstectonics; Science and Technology; Nature and Environment; subduction zones; earthquakes; earthquake magnitudes; earthquake risk; seismology; seismicity; seismic risk; models; deformation; Chile-Peru Forearc; Nazca Plate; South America Plate
Illustrationslocation maps; geoscientific sketch maps; 3-D models; plots; profiles
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2019 09 06
AbstractTension cracks were generated by past megathrust earthquakes along the coastal forearc of Chile-Peru. To explain why elastic rebound in an offshore earthquake can cause widespread permanent deformation onshore, we propose a model in which the near-surface material exhibits viscoelastic behavior, analogous to laboratory-observed behavior of petroleum reservoir rocks. Because of near-surface relaxation, interseismic deformation builds up stress only in the deeper crust. Elastic rebound of the deeper crust during an earthquake induces near-surface tension to generate cracks. We numerically demonstrate the proposed mechanism using hypothetical and real megathrust earthquakes. The location of the zone of peak tension, assumed to be responsible for the crack generation, is controlled by downdip rupture termination. A rupture farther downdip or terminating more gradually causes the zone of peak tension to be farther landward and broader. The tension cracks thus may contain important information on megathrust rupture dynamics.
Summary(Plain Language Summary, not published)
Earthquakes are the operation of elastic rebound. Tension cracks induced by megathrust earthquakes observed in Chile-Peru therefore require special explanation. In this work, we propose a testable model for these cracks. We propose that the cemented soil and the highly fractured shallow bedrock in this area exhibit a viscoelastic behavior analogous to petroleum reservoir rocks. When the megathrust is locked in preparation for the next earthquake, the deeper crust is elastically shortened like a spring, but the shallow material deforms in a viscous fashion and do not store energy. During the megathrust earthquake, elastic rebound of the deeper crust induces tension in the shallow material, causing it to crack. If we assume the observed crack distribution is controlled by the peak tension during the earthquake, it can be used to constrain how the megathrust rupture terminates in the deep end, which helps to understand the physics of earthquakes.

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