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 (M w 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 M w 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.

Fault kinematics in northern Central America and coupling along the subduction interface of the Cocos Plate, from GPS data in Chiapas (Mexico), Guatemala and El Salvador

“…Such dextral shear is in agreement with previous GPS measurements in Guatemala by Lyon‐Caen et al (2006). Similar rates are also observed by GPS in El Salvador and Nicaragua (≃15 mm yr −1 , Turner et al 2007; Correa‐Mora et al 2009; Alvarado et al 2011) and Costa‐Rica (Norabuena et al 2004) or attested by dextral mechanisms of recent crustal earthquakes ( M 6.6, 2001 February 13 earthquake in El Salvador in particular, Canora et al 2010). It can be interpreted as dextral slip on a northwest‐striking, intraarc, subvertical fault, bounding to the north an independent forearc sliver.…”

Structural evolution of the El Salvador Fault Zone: an evolving fault system within a volcanic arc.

“…The ESFZ appears as a complex network of traces (Fig.2), and it is divided in various major rupture segments based upon their different geometry, kinematics and geomorphic expression (Canora et al, 2010). The segmentation is based on detailed field observations conducted along the fault zone, from the Ilopango Caldera to the Berlin volcano area (~70 km, Fig.2), and is coherent with the seismic series of February 2001 in terms of location, rupture limits and magnitude.…”

“…The El Salvador Fault Zone (ESFZ) is one of these features, extending along the El Salvador volcanic arc (Fig 1) for about 150 km long as a right-lateral strike-slip fault system, as wide as 20 km (Martínez-Díaz et al, 2004). The ESFZ was firstly identified after the 13 th February 2001 Mw 6.6 El Salvador earthquake that ruptures the 21 km long San Vicente segment (Canora et al, 2010). Ruptures along the ESFZ are responsible for most of the historical destructive earthquakes along the El Salvador Volcanic Arc, as well as for of the current small to medium size earthquakes occurring in the area (Canora et al, 2010).…”

“…The ESFZ was firstly identified after the 13 th February 2001 Mw 6.6 El Salvador earthquake that ruptures the 21 km long San Vicente segment (Canora et al, 2010). Ruptures along the ESFZ are responsible for most of the historical destructive earthquakes along the El Salvador Volcanic Arc, as well as for of the current small to medium size earthquakes occurring in the area (Canora et al, 2010).…”

Neotectonic development of the El Salvador Fault Zone and implications for deformation in the Central America Volcanic Arc: Insights from 4-D analog modeling experiments

“…This fault zone is situated in the Central America Volcanic Arc (CAVA) near the western limit of the Chortis Block within the Caribbean plate [ Martinez‐Diaz et al ., ]. Although several studies have described the geometry and present‐day kinematics of the ESFZ [ Martinez‐Diaz et al ., ; Corti et al ., ; Agostini et al ., ; Canora et al ., , ], few studies have dealt with its development and evolution. Recent studies by Canora et al .…”