Sesimicity of the Pejibaye-Matina, Costa Rica, region: A strike-slip tectonic boundary?

Abstract

Earthquake locations are provided in an effort to determine fault orientations and investigate the existence of a strike-slip tectonic boundary on the Caribbean coast of Costa Rica. A data set of 121 earthquakes for the 1993 Pejibaye de Turrialba seismic sequence were relocated from near-field seismic stations. The epicentral distribution shows scattered background seismicity with two clusters, one near Pejibaye and another close to the Chirripo fault. At Pejibaye, the earthquake distribution trends northeast and parallels several small faults. This alignment is in agreement with the northeast plane of focal mechanism for the 1993 Pejibaye earthquake. The group of earthquakes near the Chirripo fault is associated with a northwest-trending offshore fault that also generated the 1991 Limon earthquake. Seismicity, faulting and crustal deformation are not consistent with erlier interpretations of an east-northeast oriented strike-slip tectonic boundary in the area.