Seismic imaging of a fluid storage in the actively extending Apennine mountain belt, southern Italy
Amoroso O. 1, Ascione A.2, Mazzoli S.2, Virieux J.3, Zollo A.1
1 Dipartimento di Fisica, Università degli Studi di Napoli Federico II
2 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo San Marcellino 10, 80138 Napoli, Italy
3ISTerre, Université de Grenoble I, CNRS, Grenoble, France
Geophysical Research Letters, 41, 3802–3809, 2014
A picture of the upper crustal structure of the Irpinia active faults system in southern Italy was obtained by combining new geological evidences, lithological properties, and microseismicity distribution. P and S wave velocity models indicate high VP/VS and low VP×VS values, suggesting fluid accumulation within a ~15 kmwide rock volume where intensemicroseismicity is located. The 1980 Irpinia,Ms 6.9, earthquake nucleated within the same fault-bounded volume. We suggest that concentration of background seismicity is mainly controlled by high pore fluid pressure. Its increase in fluid-filled cracks around major faults leads to earthquakes’ nucleation. Seismic pumping along major faults carries fluids through the conduit system represented by the intensely fractured damage zone. Conversely, the cross-fault barrier behavior of the low-permeability fault core leads to pore fluid pressures building up within the fault-bounded block, thus producing a positive feedback triggering earthquake nucleation within the volume, which behaves as an “earthquake reservoir.”
Three-dimensional tomographic model. (a) VP velocity model and micro-earthquake locations projected onto the cross section located in Figure 1a (refer to Figure 1b for the tectonic contacts and geological units). Grey-dashed curves delimit the well-resolved regions of the model according to the checkerboard resolution test (see section 3). Each curve corresponds to a different resolution scale obtained from estimating the resolvability function for each model parametrization used in the multiscale approach. Star shows hypocenter of the Ms 6.9, 1980 Irpinia earthquake. (b) VP/VS ratio for the same depth section as in Figure 3a. (c) VP Å~ VS product for the same depth section as in Figure 3a. (d) Horizontal slice through the P wave tomographic model at depths (Z) of 6 and 8 km. (e) Horizontal slice showing VP/VS ratio at depths (Z) of 6 and 8 km. (f) Horizontal slice showing VP Å~ VS product at depths (Z) of 6 and 8 km.