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TitleTrench-breaching afterslip following deeper coseismic slip of the 2012 Mw 7.6 Costa Rica earthquake constrained by near-trench pressure and land-based geodetic observations
AuthorSun, TORCID logo; Davis, E EORCID logo; Wang, KORCID logo; Jiang, YORCID logo
SourceEarth and Planetary Science Letters vol. 479, 2017 p. 263-272, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170176
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
AreaCosta Rica
Lat/Long WENS -86.5000 -85.0000 11.0000 9.0000
Subjectsearthquakes; faults, thrust; subduction zones; tsunami; ocean trenches; seismicity; tectonic setting; tectonic zones; Tohoku-oki earthquake; Middle America trench
Illustrationslocation maps; tables; graphs; plots; 3-D models
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2017 10 05
AbstractLarge rupture of the shallowest portion of subduction thrust faults (megathrusts), such as during the 2011 moment magnitude (Mw) 9.0 Tohoku-oki earthquake, can generate the world's most devastating tsunamis. However, it remains unclear whether such trench-breaching rupture is typical of other subduction earthquakes. The main difficulty in answering this question is the common lack of near-trench geodetic monitoring in subduction zones worldwide. Seafloor and sub-seafloor fluid pressure measurements at two closely located borehole observatories in the Middle America trench have provided clear evidence for the absence of trench-breaching rupture during the 2012 Mw 7.6 Costa Rica earthquake, and for the presence of substantial trench-breaching afterslip at slow rates after the rupture [Davis et al., 2015]. In this study, we compare postseismic seafloor pressure change at the trench with coastal Global Navigation Satellite System (GNSS) displacements. The same temporal characteristics of the deformation at the trench and coastal sites indicate that both offshore and onshore deformation were the consequence of afterslip that occurred over a wide spatial range updip of the rupture. By determining the co- and post-seismic slip distributions and inferring the associated shear stress changes on the megathrust, we show that the mechanical behaviour varies in the dip direction. The slip behaviour of the shallow megathrust at Costa Rica is consistent with conventional conceptual models, and contrasts with the behaviour of the shallowest megathrust during the Tohoku-oki event.
Summary(Plain Language Summary, not published)
Understanding the slip behaviour of the shallowest segment of subduction megathrusts is important to understanding the generation of tsunamis by subduction earthquakes, but observations are limited because of the paucity of near-trench observations. The 2011 Tohoku-oki earthquake was observed to have breached the trench, causing a devastating tsunami, but it is not clear whether this behaviour is common. In this work, we used borehole fluid pressure observations to constrain shallow megathrust behaviour at the Costa Rica subduction zone. We found that the behaviour is opposite of Tohoku-oki, illustrating the possibility of a broad spectrum of slip behaviour in this type of setting.

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