Hydrological Effects on Seismic‐Noise Monitoring in Karstic Media. Issue 15 (27th July 2021)

• Record Type: Journal Article
• Authors: Almagro Vidal, C.; Zaccarelli, L.; Pintori, F.; Bragato, P. L.; Serpelloni, E.
• Is Part Of: Geophysical research letters. Volume 48:Issue 15(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-27
• Subjects: seismic ambient noise -- seismic‐noise based monitoring -- hydrological cycle; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL093191
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Fluctuations in groundwater content may produce surface deformation and affect the elastic properties of the Earth's crust. In this study, we evaluate the temporal variations of the Earth's crust elastic properties (in the form of relative seismic‐velocity variations) in a tectonically active region in Northern Italy characterized by the presence of karst systems. In this area, GPS measurements already revealed hydrologically‐induced deformation, modulated by changes in groundwater storage. We study the relation of our seismological observations with the geodetic and hydrological results and identify the effects of groundwater‐content variations in the seismic‐velocity perturbations. Our results show that hydrologically‐induced changes in karstic media produce significant seismic‐velocity perturbations, therefore its role in tectonic‐stress adjustment studies must not be ignored. Depth sensitivity analysis of our results constrain the crustal perturbations to range between 500 and 3, 500 m depth. Results from scattering imaging locate the crustal perturbations along the main local karst systems. Plain Language Summary: Variations of water content in the ground can produce not only significant deformation of the Earth's surface but also important perturbations in the elastic properties of the crust in depth. The presence of karst in the ground can increase the magnitude and depth range of these hydrologically‐induced perturbations. In this work, we study a tectonically active area with karst systems and employ a noise‐based monitoring technique that is widely used for studying the elastic‐property perturbations produced in the ground before, during and after earthquake occurrences. Our results show that the elastic‐property perturbations in the study area are not related to the local seismicity but to the groundwater‐content variations. In the case of strong episodes of hydrological recharge (such as heavy storms), an abrupt variation of groundwater content can generate an elastic‐property perturbation equivalent to that expected from an earthquake. We locate the elastic‐property perturbations along the morphological features corresponding to the main karst systems and estimate their depth range within the first 4 km of depth, corresponding to the main carbonatic formations in the study area. Key Points: Ambient noise is successfully employed in the monitoring of the hydrological cycle in a karst environment Eight‐year long measurements enabled the observation of seismic perturbations not related to seismicity but to variations of groundwater content Depth range of the seismic perturbations varies between 500 and 3, 500 m, and its lateral detection is confirmed along the local karst systems