Abstract

QUINTERO-QUINTERO, Ronni; CAMPOS-DURAN, Daniela; PORRAS-ESPINOZA, Hernán  and  SEGURA-TORRES, Juan. Interplate earthquake analysis, central Pacific of Costa Rica: the Esterillos (November 13, 2017) and Herradura (August 24, 2020) earthquakes. Bol. Soc. Geol. Mex [online]. 2021, vol.73, n.2, 00014.  Epub Jan 31, 2022. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2021v73n2a100121.

Two strong earthquakes occurred on November 13, 2017, 02:28:20 (Esterillos Earthquake) and August 24, 2020 at 21:51:08 (Herradura Earthquake) in the Central Pacific of Costa Rica and are analyzed in this work. Herradura earthquake was located at latitude 9.501° N, longitude 84.665° W, with centroid at 25 km depth, Mw 5.9, and +1.3 seconds after the origin time. It is associated with an inverse fault striking northwest (311°), dipping to the northeast at a low angle of 20° and with a slip angle of 98°. The earthquake was reported felt from strong to very strong; keeping a close relation with the peak accelerations (PGA) registered instrumentally; this data allowed determined that the maximum intensity in the scale of Modified Mercalli (MMI) was of VI, corresponding to 12%g. Esterillos earthquake, was located 14 km southeast of the Herradura earthquake, with centroid at 21 km depth, Mw 6.4. The chosen fault plane where the event originated is striking 289° to the NW, dipping 17° to the northeast and with a slip angle of 85°, with circular form slip distribution, reaching maximum of 0.6 m around the centroid and with a radius of ~8 km. These earthquakes are located at the seismic interface of the Cocos and Caribbean plates (CO-CA) and most of the aftershocks were recorded in the first 25 km depth and with epicenters between the coast and the Middle America Trench (MAT). Cortical Caribbean events were located after the Esterillos event and close to it epicenter, the transtensional deformation in the continental Esterillos epicentral area and confirmed with calculated focal mechanism for some of these events could be related to subducted seamount in the zone.

Keywords : Central Pacific; earthquake; location; focal mechanism; aftershocks.