Ground motion scenarios for the 1997 Colfiorito, central Italy, earthquake

A Zollo A Zollo,G Franceschina G Franceschina,G Cultrera G Cultrera,F Pacor F Pacor,A Emolo A Emolo,V Convertito V Convertito,M Cocco M Cocco

doi:10.4401/ag-4452

Abstract

In this paper we report the results of several investigations aimed at evaluating ground motion scenarios for the September 26th, 1997 Colfiorito earthquake (Mw 6.0, 09:40 UTC). We model the observed variability of ground motions through synthetic scenarios which simulate an earthquake rupture propagating at constant rupture velocity (2.7 km/s) and the inferred directivity. We discuss the variability of kinematic source parameters, such as the nucleation position and the rupture velocity, and how it influences the predicted ground motions and it does not account for the total standard deviation of the empirical predictive model valid for the region. Finally, we used the results from the scenario studies for the Colfiorito earthquake to integrate the probabilistic and deterministic approaches for seismic hazard assessment.

Highlights

Following the occurrence of the 1997 Umbria-Marche seismic sequence, several Italian research projects focused on this sector of the Apennines to promote a better understanding of the regional seismicity and seismic hazard
This figure illustrates the peak ground accelerations (PGAs) recorded during the Colfiorito earthquake as a function of the epicentral distance, and compares them with the empirical predictive model proposed for the area by Bindi et al (2006)
In this paper we summarize and discuss the major results on evaluating ground shaking scenarios for the Colfiorito earthquake

Summary

Introduction

Despite the moderate-magnitude of this earthquake, the source signature on the pattern of observed ground motions is evident (Cultrera et al, 2008). A nearly NW rupture directivity can explain the observed variability of the ground motion around the fault The relevance of this source effect during the earthquake has been confirmed by several studies aimed at imaging the kinematic rupture history through waveform modeling (e.g., Pino et al, 1999; Zollo et al, 1999; Capuano et al, 2000; Hernandez et al, 2004) as well as by the careful data analysis in Cultrera et al (2008). The spatial variability of strong ground motions can depend on the heterogeneous distribution of different source model parameters (position of the rupture nucleation point, final slip, rupture velocity, slip duration, etc...) on the fault plane This implies that a large number of synthetic seismograms must be computed to account for the complexity of the rupture history in order to obtain a representative collection of strong motion waveforms that can be used for hazard estimation. The time variable can be introduced in the deterministic scenarios in terms of return period and time of interest; the source effects (geometry, radiation pattern, and directivity) are considered in the probabilistic approach

Ground motion simulation techniques

Scenarios for the Colfiorito fault

Conclusive remarks