Imaging crustal structure in south central Costa Rica with receiver functions

Abstract

[1] An array of broadband seismometers transecting the Talamanca Range in southern Costa Rica was operated from 2005 until 2007. In combination with data from a short-period network near Quepos in central Costa Rica, this data is analyzed by the receiver function method to image the crustal structure in south-central Costa Rica. Two strong positive signals are seen in the migrated images, interpreted as the Moho (at around 35 km depth) and an intra-crustal discontinuity (15 km depth). A relatively flat crustal and Moho interface underneath the north-east flank of the Talamanca Range can be followed for a lateral distance of about 50 km parallel to the trench, with only slight changes in the overall geometry. Closer to the coast, the topography of the discontinuities shows several features, most notably a deeper Moho underneath the Talamanca Mountain Range and volcanic arc. Under the highest part of the mountain ranges, the Moho reaches a depth of about 50 km, which indicates that the mountain ranges are approximately isostatically compensated. Local deviations from the crustal thickness expected for isostatic equilibrium occur under the active volcanic arc and in south Costa Rica. In the transition region between the active volcanic arc and the Talamanca Range, both the Moho and intracrustal discontinuity appear distorted, possibly related to the southern edge of the active volcanic zone and deformation within the southern part of the Central Costa Rica Deformed Belt. Near the volcanoes Irazu and Turrialba, a shallow converter occurs, correlating with a low-velocity, low-density body seen in tomography and gravimetry. Applying a grid search for the crustal interface depth and vp/vs ratio cannot constrain vp/vs values well, but points to generally low values (<1.7) in the upper crust. This is consistent with quartz-rich rocks forming the mountain range.

Density structure and geometry of the Costa Rican subduction zone from 3-D gravity modeling and local earthquake data

“…Local earthquake seismic tomographies by Husen et al (2003a), DeShon et al (2006), Syracuse et al (2008), and Arroyo et al (2009) provide 3-D constraints on the physical properties of the subduction system. Receiver functions by Dzierma et al (2010Dzierma et al ( , 2011, respectively provide insights into the structure of the overriding plate and the geometry of the plate interface for the northwestern end of the Talamanca Range. Additionally, magneto-telluric surveys by Brasse et al (2009) andWorzewski et al (2010) provide information on the electrical properties of the lithosphere for northwestern Costa Rica and the fluid cycle of the subduction system.…”

“…Isostatic compensation along the Talamanca Range (which has the highest elevations of the southeastern Central American Isthmus) reduces the possibility of a shallow Moho. According to the Airy-type isostasy modeling of the Moho depth carried out by Dzierma et al (2010), in the presence of mass load from the Talamanca Range, the Moho reaches depths greater than 40 km. Receiver function results from Dzierma et al (2010) show a Moho at 35 km for areas of intermediate topography and becomes deeper, though less constrained, below the areas with the highest topographic elevations.…”

Estado de esfuerzos estáticos en la interface de placas Coco-Caribe en Costa Rica: Interpretación mecánica para el origen de asperezas en la zona sismogénica

“…This is the case for the area beneath the Talamanca region of Costa Rica, where the stress anomalies relative to a reference body with a density of 3.32 g/cm 3 become positive approximately at the depth contour of 60 km for the slab, between 10 and 15 km shallower than the lithosphere-asthenosphere boundary. This is observed in areas where the Moho is constrained by receiver functions (Dzierma et al, 2010) and outlined by gravity modeling (Lücke, 2014), thus providing information on the crustal thickness.…”

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“…F6). More recently, from 2004 to 2006, the German project SFB 574 operated a transect of broadband seismological stations following the same orientation as TICOSECT (Dzierma et al, 2010).…”