Why Was It so Damaging? The Lorca earthquake, 2011 May 11th

Atonio D. Aretxabala; Cristina L. Sanz
The earthquake of the 11th of May 2011 that struck the town of Lorca in the region of Murcia, in the Southeast (SE) of the Iberian Peninsula has been the one with the most destructive effects in the last sixty years in Spain. Its unpredictable and devastating effects: nine victims and direct losses of 1,650,000,000 €. The monumental architectural heritage of Lorca has been severely damaged, with an estimated cost of restoration above 50,000,000 €. As one of the heads of the local government Culture Department declared: “This seism has had the most negative impact on European Heritage since the one that partially collapsed the Basilica of Asissi, in Italy, in 1997”. The accelerations measured in the first event and in the second one, two hours later, were 0.24g (Mw 4.4) and 0.41g (Mw 5.1). The seismic resistant structural code in force, NCSR 02, determines a basic acceleration of 0.12g for the area. The seism was caused by the activity of the Alhama-Murcia Fault (FAM), known since 1979, on which epicentres were located, NE of the town centre. The amplifying effect of the ground under Lorca, exceeding the previsions of the ground coefficient C established in the NCSE 02, was one of the causes of the severe damage in the built environment. These events provide an unsurpassable opportunity to study and analyse, among other areas, the role that microzoning, urban planning and design can play in effectively mitigating hazard in the urban areas of the seismic-prone regions, where historical cities with significant heritage are sited. Planners provided with tectonic seismic local maps and detailed information of the sub-surface geology will make the right decisions in order to preserve not only lives but also the built existing environment and new buildings in future developments. Besides the evident revision of NCSE 02, other building standards should be revised to guarantee not only a correct design but also the maintenance and retrofitting of buildings not meeting the requirement of seismic resistant design and codes in force, highlighting the need to include among them heritage structures.
Earthquakes, Faults, Heritage Damages, Seismic-Resistant Structural Codes, Urban Planning in Seismic Zones
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