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San Salvador, El Salvador
San Salvador, El Salvador
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Canora C.,Complutense University of Madrid | Martinez-Diaz J.J.,Complutense University of Madrid | Villamor P.,Institute of Geological & Nuclear Sciences | Berryman K.,Institute of Geological & Nuclear Sciences | And 3 more authors.
Bulletin of the Seismological Society of America | Year: 2010

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.

Verma M.P.,Electric Research Institute of Mexico | Portugal E.,Electric Research Institute of Mexico | Gangloff S.,CNRS Hydrology and Geochemistry Laboratory of Strasbourg | Armienta M.A.,National Autonomous University of Mexico | And 5 more authors.
Geostandards and Geoanalytical Research | Year: 2015

The results of an international interlaboratory proficiency test for the determination of carbonic species are presented. Eight laboratories analysed twelve water samples (four synthetic waters, one lake water, four geothermal waters, one seawater and two petroleum waters) by two methods: (a) individual laboratory analytical procedure and (b) acid-base titration curves in tabular form following a standardised protocol. In case (b), the concentrations of carbonic species were calculated by the organiser using the (1) Hydrologists' method, (2) Geochemists' method and/or (3) initial pH and total alkalinity method. For synthetic waters, the averaged % trueness and precision of measurement of the two methods were (trueness = 7.6, precision = 9.4) and (9.0, 3.4) for total alkalinity, and (6.6, 31.0) and (7.8, 6.1) for carbonic alkalinity, respectively. This indicates that the total alkalinity calculation procedure is in general correct in the individual laboratory method, but the carbonic alkalinity calculation procedure has serious problems. The measurements of total alkalinity for lake and seawaters were in agreement in both the methods; however, the individual laboratory measurement method for geothermal and petroleum waters was conceptually incorrect. Thus, the analytical procedures for the determination of carbonic species were reviewed. To apply the Hydrologists' and/or Geochemists' methods, the location of NaHCO3EP and H2CO3EP is necessary, even for samples with pH lower than that of NaHCO3EP, and a backward titration curve after complete removal of CO2 must be performed. The initial pH and total alkalinity method is appropriate where a complete analysis of species that contribute to the alkalinity is known. © 2014 International Association of Geoanalysts.

Alvarado D.,University of Wisconsin - Madison | Alvarado D.,Chevron | DeMets C.,University of Wisconsin - Madison | Tikoff B.,University of Wisconsin - Madison | And 10 more authors.
Lithosphere | Year: 2011

We combine geodetic, structural, and paleomagnetic data from El Salvador with Global Positioning System (GPS) data from southern Honduras and Nicaragua to describe the motions of the Salvadoran and Nicaraguan forearcs and determine the location and style of faulting across the Gulf of Fonseca offset of the volcanic arcs of eastern El Salvador and western Nicaragua. Finite-element modeling of GPS measurements at 35 sites in El Salvador, southern Honduras, and Nicaragua indicates that the Nicaraguan and Salvadoran forearcs both move west to northwest, parallel to their respective trenches, at 15 ± 2 mm yr-1 (95% limit) in a Caribbean plate reference frame. The similar motions of the two forearcs, despite an ~20°-25° difference in the obliquity of subduction beneath them and absence of any significant convergence obliquity offshore from El Salvador, are consistent with a recent hypothesis that the Nicaraguan forearc pushes the Salvadoran forearc to the northwest, possibly driven by northwestward lateral escape of the Central America forearc from its collision zone with the Cocos Ridge offshore from Costa Rica. The Gulf of Fonseca and adjacent eastern El Salvador form an ~60-km-wide extensional zone with E-W elongation, determined by diffuse seismicity, GPS velocities, and numerous young, N-S-striking normal faults mapped with a 10 m digital elevation model (DEM), structural measurements, and Lidar (light detection and ranging). Strike-slip earthquakes in the Fonseca pull-apart structure and evidence for modest (~10°) vertical-axis fault block rotations from paleomagnetic measurements at 33 sites in the Fonseca pull-apart structure both indicate that extension may be accompanied by bookshelf faulting. © 2011 Geological Society of America.

Scolamacchia T.,National Autonomous University of Mexico | Pullinger C.,Lageo SA | Caballero L.,National Autonomous University of Mexico | Montalvo F.,Servicio Nacional de Estudios Territoriales | And 2 more authors.
Journal of Volcanology and Geothermal Research | Year: 2010

We report the stratigraphic sequence of the 2005 eruption of Ilamatepec volcano together with sedimentological and chemical analyses of its products. Structural and textural characteristics of the deposits indicate that the eruption was driven by a small-volume rhyolitic intrusion at shallow levels, which resulted first in the collapse of the existing hydrothermally altered fan of previous deposits inside the crater lake, driving phreatic explosions with launching of blocks on ballistic trajectories; later the magma interacted with lake waters producing several hydromagmatic pyroclastic density currents (PDCs). These flows were energetic enough to knock down pine trees up to distances of 1.8 km from the crater in the E-NE sector of the volcano. Finally, ejection of ballistic blocks that landed on previously emplaced, wet pyroclastic density current deposits, caused the generation of a lahar that flowed down the steep eastern flank toward the El Jabillal gully. Subsequent lahars occurred as a result of intense rain caused by hurricane Stan. Radiocarbon ages on paleosols and charcoal fragments, separating previous volcanogenic sequences, indicate that similar eruptions have occurred more frequently in the past centuries, than previously thought. The new data confirms that Ilamatepec volcano is one of the most active volcanoes in El Salvador. Nevertheless, more detailed studies of the eruptive sequence of Ilamatepec volcano are mandatory to establish future eruptive patterns. © 2009 Elsevier B.V. All rights reserved.

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