The Sanfandila earthquake sequence of 1998, Queretaro, Mexico: activation of an undocumented fault in the northern edge of central Trans-Mexican Volcanic Belt

A sequence of small earthquakes occurred in Central Mexico, at the northern edge of the Trans-Mexican Volcanic Belt (TMVB) in the State of Queretaro, during the first 3 months of 1998. Medium to large events in the continental regime of central Mexico are not common, but the seismic history of the region demonstrates that faults there are capable of generating destructive events. The sequence was analyzed using data from a temporary network with the goals of identifying the causative fault and its relation to regional tectonics. Employing a waveform inversion scheme adapted from a method used for regional studies, we found that the source mechanisms conform to the style of faulting (i.e. extension in the E–W direction) representative of the Taxco–San Miguel Allende Fault system. This system has been proposed as the southernmost extension of the Basin and Range (BR) Province. The spatial distribution of hypocenters and source mechanisms indicate that the seismogenic segment was a fault with an azimuth of approximately 334° with almost pure dip slip. Since events which occurred just south from this region show features which are consistent with TMVB tectonics (i.e. extension in an N–S direction), the sequence may mark the boundary between the TMVB and BR stress domains.