Definición de zonas sismogenéticas en base al gradiente geotérmico, resistencia y profundidad del límite frágil-dúctil en la corteza superior. Aplicación metodológica para el cálculo de la peligrosidad sísmica en el Sureste de España

Abstract

In this work we present a methodological approach to define seismogenic zones for seismic hazard analysis based on the relationships which can be drawn from the geothermal gradient, total strength of the upper crust and the depth of the fragile-ductile transition, and their relation with the mean focal depth and a parameter hereby defined: Seismic Density Index (number of events per km3 x 1000). A revision of the deep geophysical data available in SE Spain has led to the definition of 6 distinctive crustal blocks. Two main types of crustal blocks are identified: hot-and-weak and cold-and-strong. Hot-and-weak blocks show consistently higher geothermal gradients, lower strengths and shallower fragile-ductile depths than cold-and-strong blocks. Furthermore hot-and-weak blocks show higher seismic density indexes and shallower mean focal depths. However, two blocks biased from this relationship and so are called anomalous. According to these results four seismogenic zones can be defined in SE Spain. The a and b parameters of the Gutenberg-Richter law of each zone are consistent with the thermal and strength properties of the blocks. Zones based on the hot-and-weak blocks show higher a and b values than the cold-and-strong ones, while the anomalous blocks show values in between these extremes.