Probabilistic and deterministic hazard analysis to validate the ESI scale: the test case of 1976 Guatemala earthquake

Guatemala is one of the most seismically active countries of Central America. It has suffered several dramatic earthquakes during the last century, the most destructive of which was the event associated with the Motagua fault, occurred on 4, February 1976, that caused 23,000 deaths, and 77,200 injuries. In order to achieve a better definition of seismic hazard, we have conducted a re-evaluation of the 1976 earthquake, taking into account the environmental effects that have effectively contributed to the dramatic level of destructive impact, both in terms of loss of human life and damage affecting housing and infrastructures. The analysis of primary and secondary effects has permitted a better evaluation of seismic intensity in 24 localities that were hit by the earthquake and allowed for establishing a new epicentral Intensity, characterized by XI ESI. The new intensity values have been compared with the PGA and spectral accelerations distribution recorded during the earthquake and estimated using a probabilistic/deterministic hazard analysis approach for the target area. The integration of recorded and predicted ground motion data, with the information retrieved from many surface effects like landslides, liquefactions, ground cracks and ground deformation observed over an area of about 18,000 km2 has been investigated to better constrain the affected area and the earthquake effects. The scope of our study is to evaluate the possible correlation between the coseismic geological effects, in terms of ESI scale intensity values, along the 230 km of the fault plane and the strong motion parameters recorded and estimated using a probabilistic and determistic hazard analysis.