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A team of researchers from INGV, UNIPD, UNINA and Acquedotto Pugliese investigated the relationships between hydrological effects and crustal processes that reveal the mechanical characteristics of fault rocks responsible for earthquakes in the Apennines

A study recently published in the scientific journal 'Nature Communications', entitled “Non-linear elasticity, earthquake triggering and seasonal hydrological forcing along the Irpinia fault, Southern Italy” provides innovative insights into the processes linking seasonal variation of water masses, crustal rock elasticity and seismic activity in Irpinia.

The research, conducted as part of the multidisciplinary project Pianeta Dinamico-MYBURP (Modulation of hYdrology on stress BUildup on the IRPinia Fault), was carried out by a team of researchers from the National Institute of Geophysics and Volcanology (INGV), the University of Padua, the University of Naples Federico II and the Acquedotto Pugliese company.

“Our study has revealed how hydrological effects influence the mechanical characteristics of the fault system in Irpinia and the temporal distribution of its seismicity,” explains Nicola D'Agostino, researcher at INGV and coordinator of the research team. “To find out, we analyzed the seasonal variations of seismic wave velocity in the Earth's crust and the deformation time series from an advanced network of seismic and GNSS stations of the Irpinia Near Fault Observatory and the GNSS RING Network.” 

Researchers have discovered that the hydrological recharge of the karst aquifers of the Apennines generates natural deformations that modulate the speed of seismic waves and local seismicity. Through an innovative technique of analysis of environmental seismic noise, it was possible to measure the seasonal variations in the speed of seismic waves that cross the Earth's crust and compare them with the measurements of crustal deformation induced by hydrological effects.

“These two pieces of information allowed us to measure the variations in seismic wave velocity as a function of crustal deformation, an important parameter for quantifying the non-linearity of the elastic properties of rocks,” emphasizes Stefania Tarantino, research fellow at INGV and first author of the article.

Piero Poli, Professor at the University of Padua and co-author of the article, adds that “laboratory observations show how elastic properties vary as a function of the state of deformation of the materials (non-linear elasticity), with significant implications on the mechanical characteristics with which fault rocks respond to the accumulation of deformation that precedes earthquakes. The observed sensitivity was similar to the values ​​measured in the laboratory, confirming the validity of the scientific approach adopted”.

“Our observations also show an increase in low-magnitude seismic events (M < 3.7) in spring-summer, when the hydrological load is higher, suggesting that nonlinear elasticity may play a key role not only in minor seismic phenomena, but also in the preparation of large-magnitude earthquakes, such as the one that hit Irpinia in 1980”, underlines Aldo Zollo, Professor at the University of Naples Federico II and co-author of the article.

Gaetano Festa, Professor at the University of Naples Federico II and co-author of the article, adds that “the geographical area under study is now monitored by an advanced multi-parametric infrastructure called 'Irpinia Near Fault Observatory' and made up of seismic, geodetic and geochemical stations, as well as a seismic detection system using optical fiber (DAS), managed by the INGV and the University Federico II”.

An important aspect of the work was the synergy with the company Acquedotto Pugliese, an important public infrastructure for the drinking water supply of the Puglia region and manager of the Sorgente Sanità di Caposele, which provided essential data for understanding the relationship between hydrological effects and crustal processes. "We are particularly pleased to have offered our contribution to the realization of the study. A contribution made possible by the in-depth knowledge of the subject and by the vast experience in the field, as demonstrated, among other things, during the conference on the topic, organized with INGV in our building last May", says Domenico Laforgia, president of Acquedotto Pugliese.

The results of this study offer new perspectives to better understand and monitor the processes of accumulation and release of seismic deformation, with the aim of improving seismic risk mitigation techniques.

Link to the study

Useful links:

National Institute of Geophysics and Volcanology (INGV)

University of Padua

University of Naples Federico II

Apulian Aqueduct

Dynamic Planet Project-MYBURP

Irpinia Near Fault Observatory

GNSS RING network




Aquifers_Irpinia_1.png

Figure 1: a) Distribution of tectonic deformation intensity (color scale and velocity vectors) measured by GNSS stations of the RING network. The green areas show the distribution of karst aquifers responsible for the observed hydrological deformations. b) seismicity in the Irpinia area, activated segments and focal mechanism of the Ms 6.9 earthquake of November 23, 1980. c) Time series of the observables used in the study: Caposele spring discharge (blue), velocity variations δv/v (green) and displacement at MCRV and CAFE stations (in red). Note the close correlation between hydrological effects, velocity and displacement variations at MCRV station (located close to the karst aquifers) and the lack of correlation at CAFE (located in a more distant position). d) schematic representation of the hydrological deformations and their relationship with the recharge phases of karst aquifers.



Aquifers_Irpinia_2

Figure 2: Sensitivity analysis (β) of seismic wave velocity variations (δv/v) as a function of horizontal deformation (strain). δv/v was measured through the temporal analysis of the variations of the environmental seismic noise while the deformation was calculated through the data of the GNSS RING network stations. β is a significant parameter to define the non-linearity of the elastic properties of the Earth's crust and of the accumulation and release modalities of seismic deformation in fault zones. In a) and b) the values ​​of δv/v and deformation as a function of the annual phase (a) and of the deformation rate (b) are shown. In ch the variations of δv/v and deformation for single years are shown.