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

Abstract

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 €. 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 ϳ0.1g), 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.

Comparing observed damages and losses with modelled ones using a probabilistic approach: The Lorca 2011 case

“…Since these data in the housing census is not geo-located, the assignation of the age parameter to each dwelling was done after performing a comprehensive field visit in the urban area of Lorca. Table 1 Age distribution for the buildings in Lorca Also, based on previous studies (Benito et al 2005) and making use of the age distribution, a vulnerability classification based on the EMS-98 scale (Grünthal 1998) using the data of Table 2 was prepared. It can be seen from the table that structures are classified in categories between A and D on said scale.…”

“…By having defined the age and vulnerability class distribution, several building classes were identified from the information collected by Benito et al (2005). A vulnerability class according to the EMS-98 scale has been assigned to each building class.…”

“…By combining the above mentioned two parameters for all the elements, a unique building class was assigned to each element, with a total of 10 building classes used for the analysis. Table 4 shows the building classes which were identified and assigned for this study together with the vulnerability classes proposed by Benito et al (2005). In the second column an abbreviation code is included whereas in the third column the classification according to the EMS-98 vulnerability scale is shown.…”

“…Studies to estimate seismic damages and losses in the Murcia region have been performed in the recent past. The first one was conducted before the 2011 earthquake (Benito et al 2005) where the probability of exceeding certain damage levels was obtained for the Murcia region. The second one was performed afterwards the earthquake, using a probabilistic approach to estimate future losses expressed in terms of a loss exceedance curve (Valcárcel et al 2012).…”

Rupture directivity of the 2011, Mw 5.2 Lorca earthquake (Spain)

“…From a seismological point of view, the 2011 earthquake was not an outstanding event in its regional context. In Murcia, three recent Mw 4.8, 5.0 and 4.8 earthquakes have occurred in 1999, 2002 and 2005, respectively [ Mancilla et al , 2002; Stich et al , 2006; Benito et al , 2007]. The 2011 Lorca earthquake, however, was very shallow and a bull’s eye in a densely populated urban area of ∼92.000 inhabitants.…”