Analysis of the spatial and temporal distribution of the 2001 earthquakes in El Salvador

This paper presents a study of the spatial and temporal distribution of the large destructive earthquakes that occurred in El Salvador during January and February 2001, together with the static stress transfer after each main shock, associated with their respective rupture processes. The sequence began with the magnitude M W 7.7 earthquake of 13 January, located off the western Pacifi c Coast in the subduction zone between the Cocos and Caribbean plates. One month later, a second destructive earthquake of M W 6.6 occurred in the Caribbean plate farther inland, the epicenter of which was located near San Pedro Nonualco. This shock was linked to the local faults beneath the volcanic arc and also produced signifi cant damage. The two main shocks and their aftershock sequences, together with other minor events that followed successively, produced unusually intense activity in the zone, in a short interval of time. The aims of this study are to document the spatial and temporal evolution of each seismic sequence and also to understand the possible interaction between the different events. We have inferred that some events with M > 5 triggered other shocks with the same or different origin (subduction zone or local crustal faults). The Coulomb stress transfer has been studied, and some models developed, using the rupture parameters derived from the geometric distribution of aftershocks. These results suggest the existence of a dynamic interaction, since the 13 February event occurred in a zone where the Coulomb stress increased following the January 13 event. Subsequently, some further events with magnitude around M W 5 in turn were located in other zones of increased stress associated with the two previous large earthquakes.