Low shear velocity in a normal fault system imaged by ambient noise cross correlation: The case of the Irpinia fault zone, Southern Italy

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.

Fault Pattern and Seismotectonic Style of the Campania – Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints

“…Otherwise, both might be controlled by pre-existing E-W crust-scale discontinuities. As a matter of fact, heat flow data and shear waves pattern highlight such a configuration (Vassallo et al, 2016).…”

“…Since the 1980-EQ, diffuse background seismicity with a few small-to-moderate events (M w < 5.0) have been recorded (De Matteis et al, 2012;Stabile et al, 2012;Amoroso et al, 2014;De Landro et al, 2015;Vassallo et al, 2016). Destructive earthquakes have occurred historically (Figure 1C; Porfido et al, 2002;Rovida et al, 2019).…”

“…This seismicity of the Campania-Lucania area is monitored by the Italian Seismic Network and by a local network (Irpinia Seismic Network, ISNet, Iannaccone et al, 2010). The large amount of available data has allowed refinement of the velocity models and constrain the seismicity distribution and focal mechanisms (De Matteis et al, 2012;Stabile et al, 2012;Amoroso et al, 2014;De Landro et al, 2015;Vassallo et al, 2016;Adinolfi et al, 2019). The area is mainly characterized by low-to-moderate recurrent seismicity (M L ≤ 3.0) at upper crustal depths and defined as background seismicity by De Matteis et al, 2012.…”

Insights into Mechanical Properties of the 1980 Irpinia Fault System from the Analysis of a Seismic Sequence

“…The background low magnitude seismicity appears to be spread into a large volume, and the related stress field is closely linked with the major fault segments activated during the 1980 Irpinia earthquake. In addition, microseismicity seems to be controlled by high pore pressure of water-saturated Apulian carbonates within a fault-bounded crustal volume [15,50]. Location of microseismicity epicentres is shown in Figure 1.…”

Ambient Noise Tomography of Upper Crustal Structures and Quaternary Faults in the Seoul Metropolitan Area and Its Geological Implications

“…Ambient noise tomography was applied for local geological structures such as faults, geological and geophysical features (Lin et al, 2013;Liu et al, 2018;Vassallo et al, 2016;Zigone et al, 2015). Lateral distribution of velocity anomalies is observed around faults (Li et al, 2016;Liu et al, 2018;Zheng et al, 2021).…”