Abstract
We investigate the rupture history of the three largest magnitude earthquakes of the 1997 Umbria-Marche sequence by inverting GPS, DInSAR and near-source strong motion waveforms. We use the frequency domain inversion procedure proposed by Cotton and Campillo (1995) and calculate the Green's functions for a layered half-space using the discrete wavenumber and reflectivity methods. We first invert GPS measurements and DInSAR interferograms to image the coseismic slip distribution on the fault planes in a layered half space for the two earthquakes that occurred on September 26, 1997 at 00:33 UTC (Mw = 5.7) and 09:40 UTC (Mw = 6.0) near Colfiori-to. We also invert DInSAR interferograms to infer the slip distribution during the subsequent earthquake that occurred on October 14, 1997 at 15:23 UTC (Mw = 5.6) in the SE section of the seismogenic zone near Sellano. We also explore the set of acceptable solutions using a genetic algorithm to have information on the available resolution of geodetic data. The slip models obtained by geodetic data inversion are used to perform a forward mod-eling of strong motion waveforms for all three events. We adopt a constant rupture velocity of 2.6 km/s and a constant rise time of 1 s. Our results show that these rupture models provide an acceptable fit to recorded waveforms. Finally, we invert the recorded ground displacements, collected during the September 26th 09:40 main shock and the October 14th Sellano earthquake, to constrain the rupture history. We use the geodetic slip distribution as starting model for the iterative inversion procedure. The retrieved rupture models are consistent with those inferred from geodetic data and yield a good fit to recorded seismograms. These rupture models are characterized by a heterogeneous slip distribution and an evident rupture directivity in agreement with previous observations.
Highlights
The 1997-1998 Umbria-Marche seismic sequence struck the northern part of the Apennines and it is characterized by six earthquakes with magnitude larger than 5.0 and more than 2000 smaller shocks (Deschamps et al, 2000; Chiaraluce et al, 2003)
The geodetic data set comprises the deformation pattern resulting from Differential Interferometry Synthetic Aperture Radar (DInSAR) and the vertical and horizontal displacements measured through the Global Positioning System (GPS)
The fit to the GPS displacements resulting from model M7 is shown in fig. 3 while the fit to DInSAR observations is displayed in fig. 6a
Summary
The 1997-1998 Umbria-Marche (central Italy) seismic sequence struck the northern part of the Apennines and it is characterized by six earthquakes with magnitude larger than 5.0 (see Amato et al, 1998; Ekström et al, 1998) and more than 2000 smaller shocks (Deschamps et al, 2000; Chiaraluce et al, 2003). The aim of this paper is to study the rupture history of the three main shocks of the 19971998 sequence by the inversion of geodetic (GPS and DInSAR) data and strong motion seismograms. Despite their moderate magnitude, these events allowed the collection of a multidisciplinary and accurate data set, which are very useful to constrain the slip distribution and the rupture propagation on the three main fault segments.
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