Terremoto de Benavente de 1909 (Intensidad X, Portugal)Uso de efectos geológicos para la determinación de la fuente sísmica

Abstract

The Environmental Seismic Intensity Scale (ESI-07) appeared after the exclusion of natural effects for intensity assignments in the new European Macroseismic Scale (EMS-98). This scale allows the evaluation of the intensity exclusively from ear- thquake environmental effects (EAEs), applicable in unpopulated areas without buildings, areas where damage has been saturated by extensive devastation and of use for any historical or prehistoric period. The scale provides a quantitative inten- sity assessment from geological, hydrological, geomorphological and environmental anomalies associated with each of the intensity degrees (Guerrieri and Vittori, 2007). The EAEs featured in the ESI scale provide essential information for seismic source assessment, especially for historical earthquakes where the intensity values are calculated trough building damage, no sufficient for source location. The 1909 Benavente earthquake (Intensity X) is one of these cases. This event devastated at least seven towns (most of the buildings collapsed or were demolished), producing saturation on the MM intensity scale. On the other hand, the intensity data for the epicentral area are quite biased due to the existence of large crop areas (barely populated) and an unequal geographical distribution of populations on both sides of the Tagus Valley. This paper presents the ESI-classification of the variety of EAEs described in the field report produced by Choffat and Bensaude (1912), to explore the most feasible location for the responsible seismic source.