Paleoseismological uncertainty estimation in the Acambay region, Central Mexico

Abstract

Paleseismological studies provide valuable information of the earthquake rupture processes such as fault dimensions, average and maximum displacements, as well as recurrence times and magnitudes of events which took place in the geologic past. This information is based on observations of the geological record. Interpretation of geological observations has a source of uncertainties inherent to the large number of hypotheses that explain the observed geological features. Information obtained from paleoseismic studies is im-portant in seismic hazard analyses, and particularly crucial for regions of low seismic activity where the recurrence period of major earthquakes reaches several thousand years. However, using this information in hazard analysis requires the systematic treatment of uncertainties. We estimated uncertainties of four paleoseismological studies conducted at three different faults of the Acambay graben region in Central Mexico. The method used is based on a logic-tree formalism that quantifies the cumulative uncertainties associated with the different stages of the paleoseismic studies together with a quantification of the entropy at each step and at the end of the process. The final uncertainty and its relative importance in seismic hazard analysis is expressed as the paleoseismic quality factor, which indicate 0.14, 0.40-0.50, and 0.41 for the Acambay-Tixmadejé, Pastores and San Mateo faults, respectively. These values can be incorporated in seismic hazard analyses for the region.