The Historical Seismicity of the Puebla-Tlaxcala Region (Trans-Mexican Volcanic Belt) during Early Novohispanic Times (AD 1542-1740) and the Structure of the Tlaxcala-Huamantla Half-Graben

This article documents earthquake intensity observations during early novohispanic times (A.D. 1542-1740) in the Puebla-Tlaxcala region (central Mexico), mostly based on Nahuatl-language historical annals and chronicles, and includes (as a supplement) a descriptive earthquake catalog for this period. Although it is difficult to assign intensities from fragmentary accounts, the largest shocks (A.D. 1582 and 1711) caused damage through the entire region. Earthquake ground shaking in the study area, located within the active volcanic arc crossing central Mexico, can result from intraslab normal faulting in the subducted Cocos plate, subduction interface thrust earthquakes, motion on the faults of the intra-arc Tlaxcala-Huamantla half-graben, as well as extension accommodated through magmatic injection. Most of the historical sources describe earthquakes felt only locally and sometimes report prolonged sequences of shocks, which is indicative of magmatic dike-induced earthquakes or else resulted from motion on the faults of the Tlaxcala-Huamantla half-graben. This structure, similar to 70 km long and 15-20 km wide, is the only major tectonic depression in the eastern part of the transMexican volcanic belt. It is filled by a volcano-sedimentary sequence, up to 400 m thick, of unknown but likely Pliocene age. The half-graben is bound in the north by an east- west-striking and south-dipping normal fault system, which is morphologically most pronounced near the town of Tlaxcala where the footwall uplift reaches a maximum of 350 m. The fault array is likely to be active; it vertically displaces Quaternary Totolqueme volcano.