Seismic Demands as a Result of Directivity Effects from the Mw 5.1 2011 Lorca (Spain) Earthquake

The May 11th 2011, Lorca earthquake in Southeastern Spain was a damaging event, especially considering its relatively low magnitude (Mw 5.1), which produced 9 fatalities, more than 300 injuries, and more than 462 million Euros in economic loses. Recorded ground motions and corresponding spectral ordinates significantly exceed those in current Spanish probabilistic seismic hazard models, as well as those in the Eurocode and Spanish building codes. A pulse directivity effect has been postulated by several investigators to explain these differences, the objective of this paper is to assess such effects on ground motions recorded at the LOR station during the 2011 Lorca earthquake, and to evaluate the significance of these effects on earthquake resistant design in moderate seismic regions. First, we studied the likelihood of the presence of a directivity pulse, by comparing different parameters of the recorded ground motions to analytical pulses. Additionally, we present a novel technique to extract directivity pulse features, based on the match of the response spectrum of a simple analytical pulse and the spectrum of the recorded ground motion. In a second part, we relate the inelastic displacement spectra to some models that try to capture the displacement demand features of earthquakes presenting directivity-pulse characteristics. We conclude that a large part of the impact caused by this relatively small earthquake owes to directivity effects, an aspect which is typically ignored, both in probabilistic seismic hazard analysis and in most building codes