Analysis of the 24 July 2001 Shallow Earthquake Mw=6.3 Recorded in the Northern Chile Altiplano

The main goal of the permanent seismic network, that is in operation in northern Chile since 1994, is to study the seismotectonic characteristics of the seismic gap associated with the large 1877 Mw ~9 previous earthquake. This network is composed by 13 short period seismic stations and their continuous recording also permitted to determine other interesting behaviors in the region like the high level of shallow seismicity observed in the continental crust. Particularly, this network recorded the complete sequence of the 24 July 2001 Mw=6.3 shallow earthquake, including the foreshock and aftershock events located inside of the coverage of the permanent network, the closest station is at only 5 km westward of the mainshock. It is interesting to point out that the shallow seismicity observed in the Chilean Altiplano is less frequent than the intense seismicity associated with the seismogenic interplate contact, however, after the occurrence of the 23 June 2001 southern Peru earthquake it was observed an increase in the shallow seismic activity in this region. Additional temporary stations were installed in order to improve the hypocentral locations. Strong motion data associated with the 24 July earthquake are also analyzed. There is also shallow activity located in the vicinity of the Guallatire active volcano, but it is not clear if this seismicity is only associated with the volcanic activity, because geological works done in the region also revealed some active fault systems in the same area. The deeper seismicity (depths between 15 y 60 km) is characterised by a planar-shaped seismic zone which dips about 45° trenchward that is almost perpendicular to the dip of the subducting slab at that depth range.