Rupture history of the 1997 umbria-Marche (central Italy) main shocks from the inversion of GPS, DInSAR and near field strong motion data

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.

[1]  Lauro Chiaraluce,et al.  Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study , 2003 .

[2]  Maurizio Ripepe,et al.  The 1997 Umbria‐Marche, Italy, Earthquake Sequence: A first look at the main shocks and aftershocks , 1998 .

[3]  C. Chiarabba,et al.  Vp and Vp/Vs images in the Mw 6.0 Colfiorito fault region (central Italy): A contribution to the understanding of seismotectonic and seismogenic processes , 2003 .

[4]  M. Bouchon A simple method to calculate Green's functions for elastic layered media , 1981 .

[5]  Didier Massonnet,et al.  A comparison between short term (Co‐Seismic) and long term (one year) slip for the Landers Earthquake: Measurements from strong motion and SAR interferometry , 1997 .

[6]  B. Kennett,et al.  Seismic Wave Propagation in Stratified Media , 1983 .

[7]  G. B. Cimini,et al.  Spatio-temporal distribution of seismic activity during the Umbria-Marche crisis, 1997 , 2000 .

[8]  E. Boschi,et al.  Rupture directivity of the major shocks in the 1997 Umbria‐Marche (central Italy) sequence from regional broadband waveforms , 1999 .

[9]  Nicola Alessandro Pino,et al.  The Umbria-Marche (central Italy) earthquakes: relation between rupture directivity and sequence evolution for the Mw > 5 shocks , 2000 .

[10]  E. Tondi,et al.  Active tectonics in the central Apennines and possible implications for seismic hazard analysis in peninsular Italy , 1997 .

[11]  Giorgio Franceschetti,et al.  The September 26, 1997 Colfiorito, Italy, earthquakes: Modeled coseismic surface displacement from SAR interferometry and GPS , 1999 .

[12]  F. Cotton,et al.  Redistribution of dynamic stress during coseismic ruptures: Evidence for fault interaction and earthquake triggering , 1999 .

[13]  F. Marra,et al.  The 1997 Umbria‐Marche (Italy) earthquake sequence: Relationship between ground deformation and seismogenic structure , 1999 .

[14]  G. Ekström,et al.  Source properties of the 1997–98 Central Italy earthquake sequence from inversion of long-period and broad-band seismograms , 2000 .

[15]  M. Ripepe,et al.  Complex Normal Faulting in the Apennines Thrust-and-Fold Belt: The 1997 Seismic Sequence in Central Italy , 2004 .

[16]  Michel Campillo,et al.  Frequency domain inversion of strong motions: Application to the 1992 Landers earthquake , 1995 .

[17]  Laura Scognamiglio,et al.  Edge-Diffracted 1-Sec Surface Waves Observed in a Small-Size Intramountain Basin (Colfiorito, Central Italy) , 2001 .

[18]  Salvatore Stramondo,et al.  Slip distribution of the 1997 Umbria‐Marche earthquake sequence: Joint inversion of GPS and synthetic aperture radar interferometry data , 2002 .

[19]  Aldo Zollo,et al.  Rupture mechanism and source parameters of Umbria-Marche mainshocks from strong motion data , 2000 .

[20]  G. Ekström,et al.  Rupture depths and source processes of the 1997-1998 earthquake sequence in central Italy , 1999 .

[21]  A. Frepoli,et al.  Contemporaneous extension and compression in the Northern Apennines from earthquake fault-plane solutions , 1997 .

[22]  Aldo Zollo,et al.  The 1997 Umbria‐Marche (central Italy) Earthquake Sequence: Insights on the mainshock ruptures from near source strong motion records , 1999 .

[23]  P. Baldi,et al.  Coseismic displacement of the 27th September 1997 Umbria - Marche (Italy) earthquakes detected by GPS: campaigns and data , 1999 .

[24]  K. Feigl,et al.  Radar interferometry and its application to changes in the Earth's surface , 1998 .

[25]  R. Basili,et al.  THE COLFIORITO EARTHQUAKE SEQUENCE OF SEPTEMBER–OCTOBER 1997: SURFACE BREAKS AND SEISMOTECTONIC IMPLICATIONS FOR THE CENTRAL APENNINES (ITALY) , 1998 .

[26]  A. Frepoli,et al.  Crustal stress regime in Italy , 1997 .

[27]  F. Marra,et al.  The 1997 Umbria-Marche earthquakes (Italy): relation between the surface tectonic breaks and the area of deformation , 2000 .

[28]  M. Tesauro,et al.  Modeling coseismic displacements resulting from SAR interferometry and GPS measurements during the 1997 Umbria-Marche seismic sequence , 2000 .

[29]  A. Tarantola Inverse problem theory : methods for data fitting and model parameter estimation , 1987 .

[30]  Michel Campillo,et al.  Contribution of radar interferometry to a two-step inversion of the kinematic process of the 1992 Landers earthquake , 1999 .

[31]  A. Dziewoński,et al.  Moment tensor analysis of the Central Italy Earthquake Sequence of September–October 1997 , 1998 .

[32]  K. Feigl,et al.  The displacement field of the Landers earthquake mapped by radar interferometry , 1993, Nature.

[33]  J. C. Savage Displacement field for an edge dislocation in a layered half‐space , 1998 .

[34]  Gregory C. Beroza,et al.  Slip distribution of the 1992 Landers earthquake and its implications for earthquake source mechanics , 1994 .

[35]  Concetta Nostro,et al.  Static stress changes and fault interaction during the 1997 Umbria-Marche earthquake sequence , 2000 .

[36]  R. Cattin,et al.  Effects of superficial layers on coseismic displacements for a dip-slip fault and geophysical implications , 1999 .

[37]  Paolo Baldi,et al.  Modelling coseismic displacements during the 1997 Umbria-Marche earthquake (central Italy) , 1999 .

[38]  Roberto Basili,et al.  Long‐duration asynchronous ground motions in the Colfiorito plain, central Italy, observed on a two‐dimensional dense array , 2003 .