Characterization of seismogenic crustal faults in the Gulf of Guayaquil, Ecuador

Abstract

Few moderate-to-strong earthquakes associated with active and capable geological faults have been documented for the southern coastal region of Ecuador. The seismic record of Ecuador initiates with the Guayaquil earthquake in 1787 (Mw 6.5), followed by the 1943 (Mw 6.2), and the most recent one in 1980 (Mw 6.1). The available data is insufficient to evaluate the seismic hazards associated with faults capable of generating seismic events of magnitude Mw≥6.0 in the region. Also, earthquakes of minor magnitudes can be disregarded as they do not induce significant ground coseismic effects. In this context, this study presents a catalog of geological faults, delineating 40 segments of capable and active faults on the sea floor of the Gulf of Guayaquil and inland segments of Guayas, Santa Elena, and El Oro provinces. This methodological approach estimates a variety of seismicity levels ranging between Mw 6.2 and Mw 7.2, with rock peak ground accelerations between 0.24 g and 0.41 g. These values have been obtained from empirical regression equations applied to the length of capable geological faults. The F-40 seismogenic structure located in the accretionary prism, close to the subduction zone, is capable of generating Mw 8.2 earthquakes and potentially causing coseismic ground damage to the city of Guayaquil located ca. 177 km to the NE. Furthermore, local tsunami hazards may affect severely areas that are densely populated, with developing industrial areas, on the coast of the Gulf of Guayaquil. This structural geological analysis provides useful new data for seismic hazard assessment.