Abstract

We present the results of the seismic deaggregation in 15 of the most important cities with the greatest seismic hazard in the south and west of the Iberian Peninsula (Spain and Portugal). The deaggregation was carried out based on the calculation of the seismic hazard in the zone, taking into account the peak horizontal acceleration with 10% probability of exceedance in 50 years (return period of 475 years).

We first performed a deaggregation study in terms of magnitude and distance in order to subsequently carry it out in azimuth. The aim of both studies is to determine the relative contribution of the different seismic foci and sources to the seismic hazard in a given location. Due to the lack of enough seismotectonic data in the study region, we could not obtain information about the contribution of specific active faults and we have not been able to include a characteristic earthquake model. However, by starting from a calculated hazard using smoothed background seismicity, it is possible to determine the contribution of the different seismic foci of the region to the seismic hazard at each location.

The results reveal that there are cities where the hazard is entirely, or almost entirely, due to the local seismicity (e.g., in Portugal: Lisbon, 87%; Coimbra, 82%; in Spain: Almería, 99%; Córdoba, 99%; Granada, 99%). We have also determined that there are cities where seismic foci at 200 km away or more can be the most important or at least contribute significantly to the hazard (e.g., Beja and Faro in Portugal and Cádiz and Huelva in Spain).

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