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

Abstract

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.

Frictional Properties of Subduction Input Sediments at an Erosive Convergent Continental Margin and Related Controls on Décollement Slip Modes: The Costa Rica Seismogenesis Project

“…Experimental conditions were defined to cover a wide range of conditions representative for shallow prograde subduction input trajectories, from the initial stages of subduction close to the ocean floor down to hypocentral depths, notably corresponding to the expected conditions of the updip limit of seismogenesis at approximately 5‐ to 6‐km depth (Arroyo et al, ). The exact ambient conditions during progressing subduction depend on many factors, such as the local geothermal gradient and the evolution of pore fluid pressure.…”

“…The well‐known seismic record along the MAT includes historic earthquakes of magnitude M w >7 and tsunamigenic earthquakes. It was used to characterize the geometry of the plate boundary interface and the extent of the seismogenic zone and to link seismicity patterns to the relief of the downgoing plate in numerous studies (Arroyo et al, ; Bilek et al, ; DeShon et al, ; Husen et al, ; Newman et al, ; Protti et al, ). DeShon et al () determined a slab dip of 19° from an aftershock sequence that followed the 1999 M w 6.4 Quepos event and delineated the megathrust.…”

“…The same data set yielded updip and downdip seismicity limits at depths of ≈10 and 30 km. However, this applies to one seismic megathrust event, and especially heterogeneous architecture oft he downgoing Cocos plate may constrain significant differences in plate bending radii and, thus, local slab geometry (Arroyo et al, , ; Dinc et al, ; Lücke & Arroyo, ).…”

From incipient island arc to doubly‐vergent orogen: A review of geodynamic models and sedimentary basin‐fills of southern Central America

“…More recent seismic studies do not indicate flat subduction and propose dip angles of up to 80° present at least to a depth of 70–100 km (e.g. Arroyo, Grevemeyer, Ranero, & von Huene, ; Dzierma, Rabbel, & Thorwart, ; Vannucchi, Morgan, Silver, et al, ). Below the Talamanca area, Lücke and Arroyo () assume a slab with a 50° in angle to a depth of 70 km and 64° for the final section to the depth of 200 km based on gravimetric data.…”

Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone

“…The subduction zone offshore Costa Rica (Figure 1a) is an active margin with abundant seismicity, fluid seeps, and mud volcanoes [e.g., Sahling et al, 2008;Kluesner et al, 2013;Arroyo et al, 2014] and is believed to be characterized by subduction erosion [e.g., Ranero and von Huene, 2000;Vannucchi et al, 2003]. Offshore the western margin of Costa Rica, the oceanic Cocos Plate subducts under the Caribbean Plate at a convergence rate of $90 mm/yr [DeMets, 2001].…”