Adding geodetic strain rate data to seismogenic contexts in the Alps and Apennines

摘要

In several seismic or potentially seismic areas deformation processes at moderate depth generate deformation at the surface, and the measurement of such surface deformation is an important boundary condition to models of the evolution of interacting blocks before, during and after earthquakes. The network of some 160 permanent GPS stations disseminated in Europe under the European Permanent Network of EUREF and the CERGOP 2 Project of the European Union, with additional local densification stations, provides a valuable contribution to the estimate of the average surface strain rate. The expected strain rate is of the order of 20 - 40 nanostrain per year, corresponding to a velocity change of a few mm/year over distances of some hundreds of km. Consequently, we require accuracies in the velocities of fractions of mm/year, and full control of systematic errors which may mask tectonic signals. Based on our systematic processing of GPS data from permanent European GPS stations covering nearly a decade (1995- 2005) we present the large scale velocity flow across most of continental Europe, and the associated strain rate field. By complementing the geodetic data with scaling relations and Gutenberg Richter parameters of the past 160 years seismicity in Friuli, we show that the estimated strain rate from GPS geodesy yields an estimated a maximum magnitude M=6.7 in Friuli, and arecurrence time of the May 1976 event somewhere between 630 and 960 years, if the fault is Andersonian and the strain rate is constant.