AN OVERVIEW OF THE SEISMOTECTONIC ACTIVITY IN THE SANDRA RIDGE, PANAMA BASIN

The Sandra Ridge is a structural feature located in the Panama Basin whose origin has been linked to the fragmentation of the former Farallones plate into the Cocos and Nazca plates around 23 Ma ago (Lonsdale, 2005). In order to get a better understanding of the seismotectonic activity in this structure, we deployed 4 OBS stations in the Panama Basin and used the records of 16 seismological stations located in the coastal region of Colombia, Ecuador, Panama and Costa Rica during the period since January 24 to March 4, 2015. We detected 153 events, which allowed the simultaneous inversion of hypocentral solutions and the minimum 1D-velocity model by using the Velest code (Kissling et al., 1994). Seismic signals were processed for estimating the attenuation of the coda waves by mean of the single isotropic scattering model proposed by Sato (1975) with the purpose of define wave propagation anomalies. Simultaneous correlation of spatial attenuation anomalies with Vp/Vs ratio values, heat flow anomalies and gravimetry data, allowed define the presence of possible magmatic emplacements in the area of confluence of the Sandra Ridge and the Panama Fracture Zone (PFZ). Historical solutions and the constraining with the first arrival polarities of two recent focal mechanisms (Jan. 31, 2015, UTC 18:57:49, and Feb. 05, 2015, UTC 04:40:54) which were estimated by the Geofon GFZ Helmholtz Zentrum, confirm that the PFZ is a right-lateral structure that could interact with the Sandra Ridge and form a weakness zone where magmatic material is rising-up.

Key words: Sandra Ridge, Caribbean plate boundaries, Coda Q attenuation, Focal Mechanisms, 1D Velocity Model.