Earthquake loss estimation in Adra (Almería, Spain). Current impact of a repetition of the 1910 Adra earthquake

Resumen

The town of Adra (Almería, Spain) has a population of 20,000 inhabitants and an urban area of 3.00 km2, approximately.The number of buildings have suffered a significant increase in the last 50 years.Adra town is situated in the SW of the Almería province (Southeast of Spain), one of the most hazardous zones of Spainfrom the point of view of seismic hazard. Historical seismicity data reveal that Adra was affected by near destructiveearthquakes in 1522 and 1804 (IX maximum intensity, EMS scale) and in 1910 (mb = 6.2). Several small earthquakes (mb= 5.0) in the south-east of Spain, for example, in 1993, 1994 (with an epicentre near Adra) and in 1999 (with an epicentreclose to Mula, Murcia) reached a VII degree of intensity (EMS scale) and a detailed macroseismic study revealed areas withdifferent intensities within the most affected towns. In the case of two Adra earthquakes dated 23 December 1993 and 4January 1994, the most relevant damage in Adra town occurred in reinforced concrete (RC) buildings of four or five storeysplaced on recent alluvial deposits. The other RC buildings only suffered light damage or remained intact, and similaroccurred with brick and masonry structures placed outside alluvial deposits. Furthermore, buildings with the same typologyplaced in areas underlain by similar surface geology, showed significant damage differentiation from place to place (somewith moderate damages and others undamaged); the only appreciable difference amongst them was the height of thebuildings (Navarro et al., 2007 [1]).The current building stock has been classified and the typology definition and fragility functions for physical elements havebeen assigned following the SYNER-G project (Pitilakis et al. eds., 2014 [2]). Therefore, 27 model building types have beenchosen to represent the current building stock. A simulation of the ground motion of the 1910 Adra earthquake has beenused as input for structural damage computation using the analytical methodology included in SELENA (Molina et al., 2010[3]). MASW and SPAC methods were used in order to include the site effects into the expected ground motion.As a summary, we have obtained that 474 160 and 973 78 buildings will suffer complete and extensive damagerespectively, that is around the 40% of the buildings in the city. Approximately the 55% of the extensive damaged buildingsand the 60% of the completed damaged buildings are reinforced concrete frame buildings with waffled-slabs floor pre-code.The economic losses in the city will be 43.1 8.5 millions Euros. Finally, it has been observed an increase of the extensivedamage in the mid-rise buildings that can be due to a coincidence between the period of the structure and the predominantperiod of the soil.The results will be used in future emergency planning in the city.