El Salvador is comprised inside one of the most tectonically and seismically active areas of Central America. It is characterized by two main zones of intense seismic activity: a) the subduction zone of the Cocos plate beneath the Caribbean plate along the Middle American Trench, with largest earthquakes of M> 8.0, b) a shear zone associated to the Central American Volcanic Chain, induced by an oblique component of the Cocos-Caribbean collision. This zone is characterized by moderate earthquakes of magnitude below 7.0, generally of tectonic rather than volcanic origin (De Mets,2001; Dewey et al.,2004). A strong earthquake (M7.7), located off the Salvadoran coast, occurred on January 13, 2001, producing more than 900 deaths and widespread damages, mainly due to earthquake-induced landslides (Baum et al., 2001, Jibson & Crone 2001; Bommer et al.,2002). This destructive earthquake was followed on February 13, 2001, by another major event localized on land, 30 km southeast of San Salvador, with a moment magnitude of 6.6 and a focal depth estimated between 10 and 30 km (MARN-SNET,2001). It produced severe and localized damages to the urban areas, and more than 300 deaths. The February event triggered additional thousands of landslides, generating the two largest landslides (Rio El Desague 1.5 million m3 and Rio Jiboa 12 million m3) of the seismic sequence (Baum et al.,2001; Bommer et al.,2002). Recent studies (Canora et al.,2010; Canora et al.,2012) have associated the February 13 earthquake to the reactivation of the San Vicente segment of the El Salvador Fault Zone, an E-W oriented strike-slip fault extending for 150 km through central El Salvador (Martinez-Diaz et al.,2004). Both earthquakes triggered also a number of soil liquefactions as well as lateral spreads, along alluvial plains and coastal flats. The high number of earthquake-induced geological effects has offered a good opportunity to re-evaluate the macroseismic parameters of the February 13 earthquake, by using the newly developed Environmental Seismic Intensity Scale (ESI2007). This scale defines earthquake intensity by taking into consideration the occurrence, size and areal distribution of earthquake environmental effects (EEE), including surface faulting, tectonic uplift and subsidence, landslides, liquefaction and tsunami (Michetti et al.,2007; Serva et al.,2015). According to the ESI2007 scale, the assessment of primary (tectonic) environmental effects, as well as the total area distribution of secondary EEEs, has provided a new value of epicentral intensity Io. A systematic comparison between intensities (MM and ESI scales) revealed differences ranging from one to two degrees, accounting for substantial differences in the damage potential. Hence, the recognition of the role in the amount and distribution of seismic damage that can be played by geological effects such as surface faulting, landslides, liquefaction, is crucial for a proper and comprehensive seismic hazard assessment. BIBLIOGRAFIA Baum R.L., Crone A. J., Escobar D., Harp E. L., Major J. J., Martinez M., Pullinger C. & Smith M. E. 2001. Assessment of landslide hazards resulting from the February 13, 2001, El Salvador earthquake. U.S. Geol. Surv Open-File Report 01-119, on-line Edition. Bommer J.J., Benito M.B., Ciudad-Real M., Lemoine A., Lopez-Menjivar M.A., Madariaga R., Mankelow J., Mendez de Hasbung P., Murphyh W., Nieto-Lovo M., Rodriguez-Pineda C.E. & Rosa H. 2002. The El Salvador earthquakes of January and February 2001: context, characteristics and implications for seismic risk. Soil Dynamics and Earthquake Engineering, 22, 389-418. Canora C., Martinez-Diaz J.J., Villamor P., Berryman K., Alvarez-Gomez J.A., Pullinger C. & Capote R. 2010. Geological and seismological analysis of the 13 February 2001 mw 6.6 El Salvador earthquake: evidence for surface rupture and implications for seismic hazard. Bulletin of the Seismological Society of America, 100 (6), 2873-2890. Canora C., Villamor P., Martinez-Diaz J.J., Berryman K.R., Alvarez-Gomez J.A., Capote R. & Hernandez W. 2012. Paleoseismic analysis of the San Vicente segment of the El Salvador Fault Zone, El Salvador, Central America. GeologicaActa, 10 (2), 103-123. De Mets C. 2001. A new estimate for present-day Cocos-Caribbean plate motion: Implications for slip along the Central American volcanic arc. Geophys. Res. Lett. 28, 4043-4046. Dewey J.W., White R.A. & Hernandez D.A. 2004. Seismicity and tectonic of El Salvador. Natural Hazards in El Salvador Rose W.I.et al. Eds, Geological Society of America, 375, 363-378. Jibson R.W. & Crone A.J. 2001. Observations and recommendations regarding landslide hazards related to the January 13, 2001 M-7.6 El Salvador Earthquake. U.S. Geol. Surv., Open-File Report 01-141, on-line Edition. MARN-SNET, 2001, (Ministerio de Medio Ambiente y Recursos Naturales-Servicio Nacional de Estudios Territoriales Local Network. Martinez-Diaz J.J., Alvarez-Gomez J.A., Benito B. & Hernandez D. 2004. Triggering of destructive earthquakes in El Salvador. Geology 32, 65-68. Michetti A.M., Esposito E., Guerrieri L., Porfido S., Serva L., Tatevossian R.E., Vittori E., Audemard F., Azuma T., Clague J., Comerci V., Gurpinar A., Mc Calpin J., Mohammadioun B., Morner N.A., Ota Y. & Roghozin E. 2007. Intensity Scale ESI 2007. La scala di Intensità ESI 2007. In Guerrieri L. & Vittori E. Eds.,Memorie Descrittive della Carta Geologica d'Italia, 74, 7-54. Serva L., Vittori E., Comerci V., Esposito E., Guerrieri L., Michetti A.M., Mohammadioun B., Mohammadioun G.C., Porfido S. & Tatevossian R.E. 2015. Earthquake Hazard and the Environmental Seismic Intensity (ESI) Scale. Pure Appl. Geophys, 172 (11), 2997-3028.
A reappraisal of geologic effects induced by February 13, 2001 El Salvador Earthquake
Violante C;
2016
Abstract
El Salvador is comprised inside one of the most tectonically and seismically active areas of Central America. It is characterized by two main zones of intense seismic activity: a) the subduction zone of the Cocos plate beneath the Caribbean plate along the Middle American Trench, with largest earthquakes of M> 8.0, b) a shear zone associated to the Central American Volcanic Chain, induced by an oblique component of the Cocos-Caribbean collision. This zone is characterized by moderate earthquakes of magnitude below 7.0, generally of tectonic rather than volcanic origin (De Mets,2001; Dewey et al.,2004). A strong earthquake (M7.7), located off the Salvadoran coast, occurred on January 13, 2001, producing more than 900 deaths and widespread damages, mainly due to earthquake-induced landslides (Baum et al., 2001, Jibson & Crone 2001; Bommer et al.,2002). This destructive earthquake was followed on February 13, 2001, by another major event localized on land, 30 km southeast of San Salvador, with a moment magnitude of 6.6 and a focal depth estimated between 10 and 30 km (MARN-SNET,2001). It produced severe and localized damages to the urban areas, and more than 300 deaths. The February event triggered additional thousands of landslides, generating the two largest landslides (Rio El Desague 1.5 million m3 and Rio Jiboa 12 million m3) of the seismic sequence (Baum et al.,2001; Bommer et al.,2002). Recent studies (Canora et al.,2010; Canora et al.,2012) have associated the February 13 earthquake to the reactivation of the San Vicente segment of the El Salvador Fault Zone, an E-W oriented strike-slip fault extending for 150 km through central El Salvador (Martinez-Diaz et al.,2004). Both earthquakes triggered also a number of soil liquefactions as well as lateral spreads, along alluvial plains and coastal flats. The high number of earthquake-induced geological effects has offered a good opportunity to re-evaluate the macroseismic parameters of the February 13 earthquake, by using the newly developed Environmental Seismic Intensity Scale (ESI2007). This scale defines earthquake intensity by taking into consideration the occurrence, size and areal distribution of earthquake environmental effects (EEE), including surface faulting, tectonic uplift and subsidence, landslides, liquefaction and tsunami (Michetti et al.,2007; Serva et al.,2015). According to the ESI2007 scale, the assessment of primary (tectonic) environmental effects, as well as the total area distribution of secondary EEEs, has provided a new value of epicentral intensity Io. A systematic comparison between intensities (MM and ESI scales) revealed differences ranging from one to two degrees, accounting for substantial differences in the damage potential. Hence, the recognition of the role in the amount and distribution of seismic damage that can be played by geological effects such as surface faulting, landslides, liquefaction, is crucial for a proper and comprehensive seismic hazard assessment. BIBLIOGRAFIA Baum R.L., Crone A. J., Escobar D., Harp E. L., Major J. J., Martinez M., Pullinger C. & Smith M. E. 2001. Assessment of landslide hazards resulting from the February 13, 2001, El Salvador earthquake. U.S. Geol. Surv Open-File Report 01-119, on-line Edition. Bommer J.J., Benito M.B., Ciudad-Real M., Lemoine A., Lopez-Menjivar M.A., Madariaga R., Mankelow J., Mendez de Hasbung P., Murphyh W., Nieto-Lovo M., Rodriguez-Pineda C.E. & Rosa H. 2002. The El Salvador earthquakes of January and February 2001: context, characteristics and implications for seismic risk. Soil Dynamics and Earthquake Engineering, 22, 389-418. Canora C., Martinez-Diaz J.J., Villamor P., Berryman K., Alvarez-Gomez J.A., Pullinger C. & Capote R. 2010. Geological and seismological analysis of the 13 February 2001 mw 6.6 El Salvador earthquake: evidence for surface rupture and implications for seismic hazard. Bulletin of the Seismological Society of America, 100 (6), 2873-2890. Canora C., Villamor P., Martinez-Diaz J.J., Berryman K.R., Alvarez-Gomez J.A., Capote R. & Hernandez W. 2012. Paleoseismic analysis of the San Vicente segment of the El Salvador Fault Zone, El Salvador, Central America. GeologicaActa, 10 (2), 103-123. De Mets C. 2001. A new estimate for present-day Cocos-Caribbean plate motion: Implications for slip along the Central American volcanic arc. Geophys. Res. Lett. 28, 4043-4046. Dewey J.W., White R.A. & Hernandez D.A. 2004. Seismicity and tectonic of El Salvador. Natural Hazards in El Salvador Rose W.I.et al. Eds, Geological Society of America, 375, 363-378. Jibson R.W. & Crone A.J. 2001. Observations and recommendations regarding landslide hazards related to the January 13, 2001 M-7.6 El Salvador Earthquake. U.S. Geol. Surv., Open-File Report 01-141, on-line Edition. MARN-SNET, 2001, (Ministerio de Medio Ambiente y Recursos Naturales-Servicio Nacional de Estudios Territoriales Local Network. Martinez-Diaz J.J., Alvarez-Gomez J.A., Benito B. & Hernandez D. 2004. Triggering of destructive earthquakes in El Salvador. Geology 32, 65-68. Michetti A.M., Esposito E., Guerrieri L., Porfido S., Serva L., Tatevossian R.E., Vittori E., Audemard F., Azuma T., Clague J., Comerci V., Gurpinar A., Mc Calpin J., Mohammadioun B., Morner N.A., Ota Y. & Roghozin E. 2007. Intensity Scale ESI 2007. La scala di Intensità ESI 2007. In Guerrieri L. & Vittori E. Eds.,Memorie Descrittive della Carta Geologica d'Italia, 74, 7-54. Serva L., Vittori E., Comerci V., Esposito E., Guerrieri L., Michetti A.M., Mohammadioun B., Mohammadioun G.C., Porfido S. & Tatevossian R.E. 2015. Earthquake Hazard and the Environmental Seismic Intensity (ESI) Scale. Pure Appl. Geophys, 172 (11), 2997-3028.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
