Estimation of the Probable Magnitude of 1763 Komárom Earthquake Using Structure Specific Analytical Fragility Functions

Abstract eng:
Pannonian Basin can be characterized as a moderate seismic region. One of the biggest known earthquakes in Hungary, which is located in the inner part of Pannonian Basin, occurred in Komárom in the 28th June of 1763. As result 91% buildings in Komárom were affected revealing damage states between light damage and total collapse. Surrounding cities were also affected as historical documental evidence supports. The earthquake was later characterized with uncertain magnitudes between 5.7 a 6.5, but the applied methods rely on the Modified Mercalli Intensity and then on empirical relationships to determine magnitude, completely disregarding the structural response analysis of real structures. Another estimation of the probable intensities of historical seismic events can be achieved if the behavior of real structures through dynamic structural analysis. The method exists and consists on modelling the structural damage due to the historical earthquake as a probabilistic event, where the relationship between the structural damage and ground motion intensity, magnitude and distance is represented by fragility functions. A version of this methodology is developed, validated and then applied for parametrical studies and preliminary estimations of the magnitude of the 1763 Komárom earthquake. To do so architectural archetypes are developed by combining structural seismic damage sources with historical surveying on historical buildings. A typical commoners’ house structural archetype is generated and modelled as 2D portal frame macromodels using OpenSees code and calibrated to simulate the in-plane shear behavior of historical adobe masonry infill walls. Incremental dynamic analysis is performed together with 30 site-specific ground motion records in order to generate analytical fragility functions for reported damage states. Historical damage reports are combined with structure specific probability-of-damage estimates and the sensitivity of the method is studied with plausible intervals of the damage estimates and different attenuation relationships. The posterior distribution of magnitude given a damage event is estimated using Bayes’ theorem. The formal framework for the use of prior distributions of distance and magnitude is presented for future developments. The framework of assumptions is tested in order to evaluate the relevance in reducing uncertainties as the calibration of the material and numerical models, material and geometric nonlinearities, the number and quality of structures falling into certain damage measures, and attenuation relations. A possible set of assumptions is interpreted from historical sources in order to assess the probable magnitude of the Komárom earthquake.

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