Low shear velocity in a normal fault system imaged by ambient noise cross correlation: The case of the Irpinia fault zone, Southern Italy. Issue 6 (4th June 2016)

• Record Type: Journal Article
• Authors: Vassallo, Maurizio; Festa, Gaetano; Bobbio, Antonella; Serra, Marcello
• Is Part Of: Journal of geophysical research. Volume 121:Issue 6(2016:Jun.)
• Page Start: 4290
• Page End: 4305
• Publication Date: 2016-06-04
• Subjects: seismic ambient noise -- surface waves -- cross‐correlation analysis -- seismic tomography -- normal fault -- wave propagation; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2015JB012410
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We extracted the Green's functions from cross correlation of ambient noise recorded at broadband stations located across the Apennine belt, Southern Italy. Continuous records at 26 seismic stations acquired for 3 years were analyzed. We found the emergence of surface waves in the whole range of the investigated distances (10–140 km) with energy confined in the frequency band 0.04–0.09 Hz. This phase reproduces Rayleigh waves generated by earthquakes in the same frequency range. Arrival time of Rayleigh waves was picked at all the couples of stations to obtain the average group velocity along the path connecting the two stations. The picks were inverted in separated frequency bands to get group velocity maps then used to obtain an S wave velocity model. Penetration depth of the model ranges between 12 and 25 km, depending on the velocity values and on the depth of the interfaces, here associated to strong velocity gradients. We found a low‐velocity anomaly in the region bounded by the two main faults that generated the 1980, M 6.9 Irpinia earthquake. A second anomaly was retrieved in the southeast part of the region and can be ascribed to a reminiscence of the Adria slab under the Apennine Chain. Key Points: Ambient noise cross‐correlation analysis in complex geological areas Study of normal active fault system by seismic ambient noise Role of fluids in nucleation and propagation of large earthquakes