Interplate seismicity at the CRISP drilling site: The 2002 Mw=6.4 Osa Earthquake at the southeastern end of the Middle America Trench

Arroyo, Ivonne G., Grevemeyer, Ingo, Ranero, César R. and von Huene, Roland (2014) Interplate seismicity at the CRISP drilling site: The 2002 Mw=6.4 Osa Earthquake at the southeastern end of the Middle America Trench Geochemistry Geophysics Geosystems, 15 (7). pp. 3035-3050. DOI 10.1002/2014GC005359.

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We investigate potential relations between variations in seafloor relief and age of the incoming plate and interplate seismicity. Westward from Osa Peninsula in Costa Rica, a major change in the character of the incoming Cocos Plate is displayed by abrupt lateral variations in seafloor depth and thermal structure. Here a Mw 6.4 thrust earthquake was followed by three aftershock clusters in June 2002. Initial relocations indicate that the main shock occurred fairly trenchward of most large earthquakes along the Middle America Trench off central Costa Rica. The earthquake sequence occurred while a temporary network of OBH and land stations ∼80 km to the northwest were deployed. By adding readings from permanent local stations, we obtain uncommon P wave coverage of a large subduction zone earthquake. We relocate this catalog using a nonlinear probabilistic approach within both, a 1-D and a 3-D P wave velocity models. The main shock occurred ∼25 km from the trench and probably along the plate interface at 5–10 km depth. We analyze teleseismic data to further constrain the rupture process of the main shock. The best depth estimates indicate that most of the seismic energy was radiated at shallow depth below the continental slope, supporting the nucleation of the Osa earthquake at ∼6 km depth. The location and depth coincide with the plate boundary imaged in prestack depth-migrated reflection lines shot near the nucleation area. Aftershocks propagated downdip to the area of a 1999 Mw 6.9 sequence and partially overlapped it. The results indicate that underthrusting of the young and buoyant Cocos Ridge has created conditions for interplate seismogenesis shallower and closer to the trench axis than elsewhere along the central Costa Rica margin.

Document Type: Article
Additional Information: WOS:000340557300019
Keywords: earthquake relocation; erosional margin; interplate drilling
Research affiliation: OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
DOI etc.: 10.1002/2014GC005359
ISSN: 1525-2027
Projects: SFB574, Future Ocean
Date Deposited: 15 Apr 2014 11:28
Last Modified: 28 Feb 2018 11:07

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