The Gorgona island, Colombia, earthquake of 10 September 2007 (Mw 6.8); rupture process and implications on the seismic hazard in the region

The subduction zone in southern Colombia and northern Ecuador has been the site of significant events in the area that broke the great 1906 earthquake in Ecuador. The 2007 earthquake on Gorgona Island is located within this area, presenting a normal-type focal mechanism and a moment magnitude Mw 6.8. This event is due to the compressive stresses exerted on the continental plate of South America by the Nazca oceanic plate. We performed a kinematic inversion source process of the Gorgona earthquake. Our results show the main slip patch at the hypocenter and a secondary slip release deeper at SW on the fault plane, which agrees with the location of aftershocks; the source time function obtained reflects these energy releases with a total duration of 15 s. We also analyzed the stress state field in this region using the focal mechanism of its early aftershock sequence, obtaining an extensive regime with an azimuth Shmin of 108° and NW-SE direction. The average interseismic coupling in this convergent margin zone is not so high as in the southern areas. Nevertheless, observations of this kind of seismicity and GPS studies in the upper plate of a subduction zone are essential in understanding earthquake cycles and, perhaps, in anticipating slip distributions in future subduction events.