Shape of Empirical and Synthetic Isoseismals: Comparison for Italian M \le 6 Earthquakes

TL;DR

This study compares empirical and synthetic isoseismal shapes for six Italian earthquakes of magnitude 4.5-6, demonstrating that low intensity isoseismals reveal source geometry with minimal parameter variation using a new visualization method.

Contribution

It introduces a new Diffuse Boundary method for visualizing isoseismals with uncertainty, and shows that low intensity isoseismals can inform about source geometry with minimal modeling parameters.

Findings

Low intensity isoseismals provide source geometry information.

The Diffuse Boundary method visualizes isoseismals with uncertainty.

Results are consistent with larger earthquakes despite fewer parameters.

Abstract

We present results from a comparative analysis of empirical and synthetic shapes for isoseismals of low intensity (I = IV-VI on the MCS scale) for six Italian earthquakes of ML = 4.5-6. Our modelling of isoseismals is based on a plane stratified earth model and on the dou-ble-couple point source approximation to calculate seismograms in the frequency range f =< 1 Hz. With a minimum of parameter variation we demonstrate that the low intensity isoseismals provide information on source geometry. We strive to avoid subjectivity in isoseismal construc-tions by using the new Diffuse Boundary method, which visualizes isoseismals with their uncer-tainty. Similar results in this direction are known for large earthquakes (ML ~ 6 or greater) with extended sources and for the higher isoseismals (I >= VI on the MM scale). The latter studies disregard the earth structure, use a greater number of parameters, and therefore have greater possibilities for fitting the data than our approach.