This work has evaluated the probability of earthquake-tr iggered landslide occurrence in the whole of El Salvador, with a Geographic Information System (GIS) and a logistic regression model. Slope gradient, elevation, aspect, mean annual precipitation, lithology, land use, and terrain roughness are the predictor variables used to determine the dependent variable of occurrence or non­ occurrence of landslides within an individual grid cell. The results illustrate the importance of terrain roughness and soil type as key factors within the model — using only these two variables the analysis returned a significance level of 89.4%. The results obtained from the model within the GIS were then used to produce a map of relative landslide susceptibility.

We investigate the existence of a mechanism of static stress triggering driven by the\ud interaction of normal faults in the Middle American subduction zone and strike-slip faults\ud in the El Salvador volcanic arc. The local geology points to a large strike-slip fault zone,\ud the El Salvador fault zone, as the source of several destructive earthquakes in El Salvador\ud along the volcanic arc. We modeled the Coulomb failure stress (CFS) change produced\ud by the June 1982 and January 2001 subduction events on planes parallel to the El Salvador\ud fault zone. The results have broad implications for future risk management in the region,\ud as they suggest a causative relationship between the position of the normal-slip events in\ud the subduction zone and the strike-slip events in the volcanic arc. After the February 2001\ud event, an important area of the El Salvador fault zone was loaded with a positive change\ud in Coulomb failure stress (.0.15 MPa). This scenario must be considered in the seismic\ud hazard assessment studies that will be carried out in this area

19 páginas, 13 figuras, 4 tablas.A detailed study of four earthquakes that occurred in the Murcia region (southeastern Spain) in 1911, 1999, and 2002 has been carried out. New intensity maps have been plotted for the March and April 1911 shocks. These show maximum values of VII–VIII (EMS). We have found values of VI and V, respectively, for the 1999 and 2002 earthquakes. Surface wave magnitudes range from 5.2 for the Bullas 2002 event to 5.7 for the March 1911 event. Focal mechanisms for the Mula 1999 and Bullas 2002 events indicate reverse and strike slip motions, with scalar seismic moments of 5.9 x 1016 N m and 8.6 x 1015 N m, respectively, and focal dimensions of 4.0 and 1.5 km. Both earthquakes were recorded at epicentral distances greater than 21 km, showing low values of peak ground acceleration (PGA) (<0.020 g). These records involve a ground motion less than the ones expected in the region, according to different hazard studies. The seismic hazard map that we obtained for the Murcia region (for a return period of 475 years) shows higher values than those given in the Spanish Building Code NCSE-02 (2002) (e.g., 0.24 g for PGA in the city of Murcia, compared with 0.16 g in the code).Peer reviewe

This paper presents a methodological approach to seismic hazard assessment based on a hybrid source model composed of faults as independent entities and zones containing residual seismicity. The seismic potential of both types of sources is derived from different data: for the zones, the recurrence model is estimated from the seismic catalogue. For fault sources, it is inferred from slip rates derived from palaeoseismicity and GNSS (Global Navigation Satellite System) measurements. Distributing the seismic potential associated with each source is a key question when considering hybrid zone and fault models, and this is normally resolved using one of two possible alternatives: (1) considering a characteristic earthquake model for the fault and assigning the remaining magnitudes to the zone, or (2) establishing a cut-off magnitude, M_c, above which the seisms are assigned to the fault and below which they are considered to have occurred in the zone. This paper presents an approach to distributing seismic potential between zones and faults without restricting the magnitudes for each type of source, precluding the need to establish cut-off M_c values beforehand. This is the essential difference between our approach and other approaches that have been applied previously. The proposed approach is applied in southern Spain, a region of low-to-moderate seismicity where faults move slowly. The results obtained are contrasted with the results of a seismic hazard method based exclusively on the zone model. Using the hybrid approach, acceleration values show a concentration of expected accelerations around fault traces, which is not appreciated in the classic approach using only zones.