Abstract

ORTEGA, Roberto; CARCIUMARU, Dana; QUINTANAR, Luis  and  RUBIO, Reynaldo. Estimation of seismic hazard in central Baja California: A consistent model between the Gulf of California and Peninsular regions. Bol. Soc. Geol. Mex [online]. 2015, vol.67, n.1, pp.87-102. ISSN 1405-3322.

We present results of a probability seismic hazard analysis in the central part of the Baja California Peninsula, which comprises mainly the Vizcaino Biosphere Reserve. This part of the peninsula has been poorly studied because it has the lowest population density of the region. However, the highest acceleration values in Baja California Sur, Mexico, during the last 15 years have been recorded in this area. It is observed that transform faults control the seismic hazard for short recurrence periods (< 1000 years), whereas the peninsular faults are of major importance for long recurrence periods (> 1000 years). Moreover, it is necessary to have a detailed map of the seismic sources, especially those from the Vizcaino valley, where sedimentary fill covers the geological structures. We propose choosing return periods that are consistent with the observed geological fault. In addition, we discuss the difficulty to conciliate the Gutenberg-Richter and Characteristic models. The Poisson distribution is not adequate for the Characteristic model in a Probabilistic Seismic Hazard Map (PSHM) because they span different time lapses; while the PSHM model is commonly used for intervals of a few hundred years, the Characteristic model for Quaternary faults is for several tens of thousands years. A simple solution for hazard maps, especially for essential facilities, is to choose a return period that corresponds to the characteristic fault that is nearest to the site. Otherwise the map will underestimate the seismic hazard even though design correction factors are applied.

Keywords : seismic hazard; Baja California Sur; Characteristic Earthquake; Poisson distribution.