Seismogenic zone structure of the southern Middle America Trench, Costa Rica

DeShon, H. R., Schwartz, S. Y., Bilek, S. L., Dorman, L. M., Gonzalez, V., Protti, J. M., Flueh, Ernst R. and Dixon, T. H. (2003) Seismogenic zone structure of the southern Middle America Trench, Costa Rica Journal of Geophysical Research - Solid Earth, 108 (B10). p. 2491. DOI 10.1029/2002JB002294.

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The shallow seismogenic portion of subduction zones generates damaging large and
great earthquakes. This study provides structural constraints on the seismogenic zone of
the Middle America Trench offshore central Costa Rica and insights into the physical
and mechanical characteristics controlling seismogenesis. We have located ~300 events
that occurred following the MW 6.9, 20 August 1999, Quepos, Costa Rica, underthrusting
earthquake using a three-dimensional velocity model and arrival time data recorded by a
temporary local network of land and ocean bottom seismometers. We use aftershock
locations to define the geometry and characteristics of the seismogenic zone in this region.
These events define a plane dipping at 19° that marks the interface between the Cocos
Plate and the Panama Block. The majority of aftershocks occur below 10 km and above
30 km depth below sea level, corresponding to 30–35 km and 95 km from the trench axis,
respectively. Relative event relocation produces a seismicity pattern similar to that
obtained using absolute locations, increasing confidence in the geometry of the
seismogenic zone. The aftershock locations spatially correlate with the downdip extension
of the oceanic Quepos Plateau and reflect the structure of the main shock rupture asperity.
This strengthens an earlier argument that the 1999 Quepos earthquake ruptured specific
bathymetric highs on the downgoing plate. We believe that subduction of this highly
disrupted seafloor has established a set of conditions which presently limit the
seismogenic zone to be between 10 and 35 km below sea level.

Document Type: Article
Keywords: seismogenic zone, Costa Rica, Quepos aftershocks, subduction zone, earthquake location
Research affiliation: OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor
OceanRep > SFB 574 > A2
Refereed: Yes
DOI etc.: 10.1029/2002JB002294
ISSN: 0148-0227
Contribution Number:
SFB 57442
Date Deposited: 07 Apr 2010 11:48
Last Modified: 13 Jan 2016 08:18

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