Earthquake damage orientation to infer seismic parameters in archaeological sites and historical earthquakes

Abstract

Studies to provide information concerning seismic parameters and seismic sources of historical and archaeological seismic events are used to better evaluate the seismic hazard of a region. This is of especial interest when no surface rupture is recorded or the seismogenic fault cannot be identified. The orientation pattern of the earthquake damage (ED) (e.g., fallen columns, dropped key stones) that affected architectonic elements of cities after earthquakes has been traditionally used in historical and archaeoseismological studies to infer seismic parameters. However, in the literature depending on the authors, the parameters that can be obtained are contradictory (it has been proposed: the epicenter location, the orientation of the P-waves, the orientation of the compressional strain and the fault kinematics) and authors even question these relations with the earthquake damage. The earthquakes of Lorca in 2011, Christchurch in 2011 and Emilia Romagna in 2012 present an opportunity to measure systematically a large number and wide variety of earthquake damage in historical buildings (the same structures that are used in historical and archaeological studies). The damage pattern orientation has been compared with modern instrumental data, which is not possible in historical and archaeoseismological studies. From measurements and quantification of the orientation patterns in the studied earthquakes, it is observed that there is a systematic pattern of the earthquake damage orientation (EDO) in the proximity of the seismic source (fault trace) (<10 km). The EDO in these earthquakes is normal to the fault trend (±15°). This orientation can be generated by a pulse of motion that in the near fault region has a distinguishable acceleration normal to the fault due to the polarization of the S-waves. Therefore, the earthquake damage orientation could be used to estimate the seismogenic fault trend of historical earthquakes studies where no instrumental data are available.