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An Overview of the Damaging and Low Magnitude M_w 4.8 La Paca Earthquake on 29 January 2005: Context, Seismotectonics, and Seismic Risk Implications for Southeast Spain

¹ ETSI Topografía, Geodesia y Cartografía
Universidad Politécnica de Madrid
28031 Madrid, Spain
 (B.B., J.M.G.-E., M.J.G.R., M.E.J.)
² Department de Geodinámica, F. CC. Geológicas
Universidad Complutense de Madrid
28003 Madrid, Spain
 (R.C., J.J.M.-D., M.T., J.M.I.-A., J.A.A.-G., C.C.)
³ Architect
Piamonte 18, 4E 28004 Madrid, Spain
 (P.M.)
⁴ Istituto Nazionale di Geofisica e Vulcanologia
40128 Bologna, Italy
 (D.S.)
⁵ Laboratorio de Geotecnia (CEDEX)
Alfonso XII, 3 Madrid 28014, Spain
 (J.G.-M.)

This article presents an overview of the La Paca earthquake of magnitude m_bLg 4.7, which occurred on 29 January 2005, with its epicenter located near the town of Avilés in the Murcia region in southeast Spain. Despite its low magnitude, the earthquake caused important damage in two towns of the epicentral area, La Paca and Zarcilla de Ramos. These areas recorded intensities of VI–VII (European Macroseismic Scale, 1998) and sustained estimated economic losses amounting to 10 million ;eu[|20ac|]. Aftershocks continued for more than 2 weeks, producing considerable alarm in the population and mobilizing emergency services from the whole region. The La Paca seismic series is the third registered in the region in the past 8 years, being preceded by the Mula (1999) and southwest Bullas (2002) seismic series. These main events had also low magnitudes (m_bLg 4.8) and caused damage levels similar to the 2005 earthquake. The case is an example of a moderate seismic zone where low-magnitude and frequent earthquakes have important implications on the seismic hazard and risk of the region. Although these are not the largest expected earthquakes, they have yielded important information for improving the knowledge of the seismic activity of the area. With this aim in mind, different topics have been analyzed from a multidisciplinary perspective, including seismicity, local tectonics and surface geology, focal mechanisms, macroseismic effects, and ground motion. Results indicate a local tectonic interpretation, consistent with a strike-slip focal mechanism, the confirmation of a triggering process between the 2002 and 2005 earthquakes, a geotechnical and ground-motion characterization for the damaged sites (supporting local amplification effects and estimated peak ground acceleration values of 0.1g), and an understanding of damage patterns in relation to local building trends. The results may be used as guidelines for future revisions of the Spanish Building Code (Norma de la Construcción Sismorresistente Española [NCSE-02], 2002). The study results should contribute to risk mitigation in a region where strong-motion records from the maximum expected earthquakes are not available. This approach can be extended to other regions with similar seismic backgrounds and a lack of strong-motion records.