Decade-long monitoring of seismic velocity changes at the Irpinia fault system (southern Italy) reveals pore pressure pulsations

G De Landro,A Zollo,R Esposito,G Russo,O Amoroso,A Emolo,N D’Agostino

doi:10.1038/s41598-022-05365-x

Abstract

Several studies have monitored crustal seismic velocity changes and attempted to relate them to the stress state and physical properties in volume embedding fault systems. The aim is to provide constraints on fault system dynamics and earthquake triggering mechanisms. Here, we reconstruct the spatiotemporal (4D) seismic velocity images of volume embedding the Irpinia fault system (IFS, South Italy), which originated the 1980 Ms 6.9 multi-segmented ruptures. By inverting data from more than ten years of continuous seismicity monitoring, we retrieved time-constant velocity anomalies, whose shapes correlate well with crustal lithology, while time-changing (up to 20%) velocity anomalies are mapped in the central region. Here, the Vp-to-Vs changes at depths of 1–5 km and 8–12 km correlate well with groundwater recharge and geodetic displacement during the same time interval. This correlation provides evidence for the existence of pulsating, pore pressure changes induced by groundwater recharge processes in a deep volume (8–12 km of depth), fractured and saturated with a predominant gas phase (likely CO2). We suggest that tomographic measurements of the Vp-to-Vs spatiotemporal changes are a suitable proxy to track the pore pressure evolution at depth in highly sensitive regions of fault systems.

Highlights

Several studies have monitored crustal seismic velocity changes and attempted to relate them to the stress state and physical properties in volume embedding fault systems
The Irpinia fault system (IFS), which is located in the southern part of the Apennine chain (Italy; Fig. 1a), generated the largest Italian event in the last 100 years: the 1980 M s 6.9 Irpinia earthquake
Since 2005, the IFS has been monitored by the Irpinia Seismic Network (ISNet; blue triangles in Fig. 1a), which is composed of 33 stations and deployed for early warning p urposes[11]

Summary

Introduction

Several studies have monitored crustal seismic velocity changes and attempted to relate them to the stress state and physical properties in volume embedding fault systems. Amoroso et al.[14] retrieved 3D tomographic P and S velocity images showing that the hypocentral volume of the 1980 Irpinia earthquake was characterized by a high Vp-to-Vs ratio, which was interpreted as being linked to the presence of fluid-saturated rocks.

Results

Conclusion