The 7 June 2007 mbLg 4.2 escopete earthquake : An event with significant ground motion in a stable zone (Central Iberian Peninsula)

Abstract

An earthquake occurred on 7 June 2007 at 01h:42m:09.5s (UTC) with geographical coordinates 40°.41N, 2°.98W and magnitude mbLg = 4.2 according to the Seismic national network (RSN) of Madrid's Instituto Geográfico Nacional (IGN). The epicenter was located close to the town of Escopete, where the earthquake was felt with intensity IV, waking up inhabitants and causing widespread alarm. Historically, rare but similar events have been felt in the area, near the towns of Pastrana (1922) and Duron (1982). Nevertheless, this part of Iberia experiences very low seismic activity. The earthquake with the largest magnitude recorded to date by the RSN since the mid-1920s was 4.1. Due to low seismicity values, the hazard map of the Norma de la Construcción Sismorresistente Española (Spanish seismic building code; NCSE-02) establishes a basic acceleration value of less than 0.04 g, which is the threshold value for the application of the earthquake-resistant building code. However, this value was exceeded in strong-motion recordings during the 2007 event. An important consideration is the existence of two nuclear power plants in the Guadalajara administrative province: José Cabrera and Trillo. Strong-motion instruments at the José Cabrera nuclear power plant (JCNPP) recorded a peak ground acceleration (PGA) value of 0.07g. This is the first acceleration recording made from central Iberia and also one of the highest values read from instruments to date for the whole of the Iberian peninsula. This paper presents an overview of the results of our multidisciplinary analysis of the earthquake, which we researched in terms of its regional and local tectonic setting, local seismicity, focal mechanics, strong-motion records, and macroseismic effects.