María C. Araya

The Guanacaste Volcanic Arc Sliver of Northwestern Costa Rica

Recent studies have shown that the Nicoya Peninsula of northwestern Costa Rica is moving northwestward ~11 mm a−1 as part of a tectonic sliver. Toward the northwest in El Salvador the northern sliver boundary is marked by a dextral strike-slip fault system active since Late Pleistocene time. To the southeast there is no consensus on what constitutes the northern boundary of the sliver, although a system of active crustal faults has been described in central Costa Rica. Here we propose that the Haciendas-Chiripa fault system serves as the northeastern boundary for the sliver and that the sliver includes most of the Guanacaste volcanic arc, herein the Guanacaste Volcanic Arc Sliver. In this paper we provide constraints on the geometry and kinematics of the boundary of the Guanacaste Volcanic Arc Sliver that are timely and essential to any models aimed at resolving the driving mechanism for sliver motion. Our results are also critical for assessing geological hazards in northwestern Costa Rica.

El sismo de Capellades del 2016 y su secuencia sísmica: Manifestación de fallamiento de rumbo en el arco volcánico de Costa Rica

espanolEl 30 de noviembre del 2016 a las 18:25 (00:25 UTC del 1 de diciembre) ocurrio un sismo de Mw 5,5 a una profundidad de 2,7 km, 4 km al norte de Capellades de Alvarado, Costa Rica. Fue el evento principal de una secuencia con precursores y replicas, localizada a 5 km de los volcanes activos Irazu y Turrialba. Este sismo es el mas reciente de una lista de terremotos originados en las fallas que cortan la Cordillera Volcanica Central, la cual representa el limite norte del area mas poblada del pais. Usando principalmente los registros instrumentales de la Red Sismologica Nacional (RSN), en este trabajo se presenta un analisis sismologico de la secuencia y se determinan la ubicacion y las caracteristicas de la falla que origino esta sismicidad. Adicionalmente, se describe el entorno geologico-tectonico de su origen y sus efectos. La secuencia de sismos muestra un claro alineamiento de 8 km de longitud y rumbo nor-noroeste, entre los volcanes Irazu y Turrialba. La interpretacion conjunta de la relocalizacion de la secuencia, el tensor de momento del sismo principal y los mecanismos focales de 17 eventos permitio determinar que la falla de origen es casi vertical y de tipo de desplazamiento de rumbo dextral, lo cual es congruente con los sistemas de fallamiento activo de la zona. Esta falla no habia sido reconocida previamente y se ha denominado Liebres en este estudio. El sismo principal fue sentido en casi todo el pais, con una intensidad maxima de VI+. Este sismo ha sido el de mayor magnitud en el sector oriental de la Cordillera Volcanica Central desde el terremoto de Patillos de 1952 (Ms 5,9) y el primer sismo de Mw > 5,0 registrado por la RSN en el edifiio volcanico del Turrialba. A pesar de la cercania con ese volcan, que ha presentado erupciones periodicas desde el 2010, no se observaron efectos eruptivos inmediatos. EnglishOn 30 November 2016 at 18:25 (1 st December at 00:25, UTC time) a Mw 5 5 earthquake occurred at 2.7 km depth, 4 km north of the town Capellades de Alvarado, Costa Rica. It was the main shock of an earthquake sequence including foreshocks and aftershocks, located 5 km from the active Irazu and Turrialba volcanoes. This is the most recent of a series of damaging earthquakes originated in the faults crossing the Central Volcanic Range, which constitutes the northern boundary of the most populated area of the country. Using mainly the seismic records from the National Seismological Network (RSN), we present in this study a seismological analysis of the earthquake sequence and the location and characteristics of the fault that originated this seismicity. Additionally, we describe the geotectonic context of the fault and the Capellades earthquake effects. The earthquake sequence shows a clear 8-km long alignment striking nor-northwest between Irazu and Turrialba volcanoes. The joint interpretation of the earthquake relocation, the main-shock moment tensor solution, and the focal mechanisms of 17 events allows for determining the source in a nearly vertical strike-slip fault, in agreement with regional active fault systems. This structure had not been recognized previously and has been named Liebres Fault in this study. The main shock was felt in most of the country, with a maximum intensity of VI+. This earthquake has been the largest in the eastern part of the Central Volcanic Range since the 1952 Patillos earthquake (Ms 5.9) and the fist Mw > 5.0 earthquake recorded by the RSN in the Turrialba volcano edifie. Despite the proximity to this active volcano, which has been erupting periodically since 2010, there were no immediate eruptive effects.

La falla Tobosi: Fuente del enjambre sísmico de Tobosi del 2011-2012 en el centro de Costa Rica

The Central Costa Rica Deformed Belt (CCRDB) is an ~100-km broad zone of deformation that marks the boundary between the Caribbean Plate and the Panama Microplate. From December 2011 to February 2012, an earthquake swarm took place in a portion of the CCRDB, near the town of Tobosi, 7 km southwest of the city of Cartago. In this study, data recorded by the National Seismological Network of Costa Rica (RSN: UCR-ICE) is used to relocate the earthquakes and calculate their focal mechanisms. Additionally, the tectonic geomorphology of the region is analyzed. The results show a transtension structure near the town of Tobosi, which comprises at least three faults, named: the Tobosi, Tablon, and Alumbre faults. It was found that the Tobosi fault is an active left-lateral strike-slip fault with a normal component and was the source of the Tobosi earthquake swarm.