Geological and Seismological Analysis of the 13 February 2001 Mw 6.6 El Salvador Earthquake: Evidence for Surface Rupture and Implications for Seismic Hazard

Abstract

The El Salvador earthquake of 13 February 2001 (Mw 6.6) caused tectonic rupture on the El Salvador fault zone (ESFZ). Right-lateral strike-slip surface rupture of the east–west trending fault zone had a maximum surface displacement of 0.60 m. No vertical component was observed. The earthquake resulted in widespread landslides in the epicentral area, where bedrock is composed of volcanic sediments, tephra, and weak ignimbrites. In the aftermath of the earthquake, widespread damage to houses and roads and the hazards posed by landslides captured the attention of responding agencies and scientists, and the presence of surface-fault rupture was overlooked. Additionally, the tectonic context in which the earthquake took place had not been clear until mapping of the ESFZ was completed for the present study.We identified several fault segments, the distribution of surface ruptures, the aftershock pattern, and fault-rupture scaling considerations that indicate the 21-km-long San Vicente segment ruptured in the 2001 event. Static Coulomb stress transfer models for the San Vicente rupture are consistent with both aftershock activity of the 2001 sequence and ongoing background seismicity in the region. At Mw 6.6, the 2001 earthquake was of only moderate magnitude, yet there was significant damage to the country’s infrastructure, including buildings and roads, and numerous deaths and injuries. Thus, earthquake hazard and risk in the vicinity of the ESFZ, which straddles the city of San Salvador with a population of >2 million, is high because even moderate-magnitude events can result in major damage, deaths, and injuries in the region.