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The M<inf>w</inf> 6.8 Macas earthquake in the Sub-Andean zone of Ecuador, October 3, 1995

Abstract:

At 01:51 on 3 October 1995 (UT) a Mw 6.8 earthquake located at 2.80°S, 77.96°W at a depth of 16 km occurred on the SE flank of Cutucu cordillera, a NNE-SSW Jurassic-Cretacic anticline, located on the western edge of the Subandean zone. While major shallow earthquakes occur in the coastal zone, the seismic hazard in the Subandean zone of Ecuador should be of major concern for the Ecuadorian authorities as, for example, all the magnitude ≥6.2 Ecuadorian events since 1985 have occurred in the Subandean zone. Moreover, for shallow earthquakes (depth ≤70 km) with magnitude ≥6.2, a clear pattern of alternate activity is apparent between the coastal and the Subandean-Andean zones since at least 1900. A possible explanation for the alternate activity between the coast and the Subandean-Andean is that the subduction is locked at times; stresses are then accommodated by the arc/back-arc zone. When the subduction process resumes, stresses are accommodated by the forearc.