Earthquake estimation from historical macroseismic data

Abstract

As part of the NERIES (Network of Research Infrastructures for European Seismology) project, a catalogue of the larger European earthquakes from 1000-1900 is being newly compiled. A problem with previous pan-European catalogues is that they all involve merging of national catalogues that were compiled in different ways, leading to inconsistencies in the final result. A fundamental goal of the NERIES catalogue is that all events should be assessed using the same homogeneous procedures from the basic raw material, i.e. the intensity data points (IDP). Defining suitable procedures is, however, far from straightforward. A number of competing methods have been proposed in the past, and the issue of calibration is problematic. After extensive surveys of current practices, a test was conducted in which some modern IDP sets were massaged to resemble historical data sets. Results suggest that methods relying on a grid-search, attenuation-fitting approach perform better than other methods. We propose here a method based on the mechanics of earthquake perception, which allows for parameter estimation in different parts of Europe without the need for separate calibration exercises. An initial epicentral estimation is made on the distribution of high intensities. This used as the starting point for fitting an intensity attenuation model, which gives the final solution of both epicentre and depth. Finally, the data set is compared to expected intensity distribution from different magnitude events to provide the estimated magnitude events to provide the estimated magnitude, Mi, equivalent o Mw.