Abstract
A seismic sequence in central Italy from August 2016 to January 2017 affected groundwater dynamics in fractured carbonate aquifers. Changes in spring discharge, water-table position, and streamflow were recorded for several months following nine Mw 5.0–6.5 seismic events. Data from 22 measurement sites, located within 100 km of the epicentral zones, were analyzed. The intensity of the induced changes were correlated with seismic magnitude and distance to epicenters. The additional post-seismic discharge from rivers and springs was found to be higher than 9 m3/s, totaling more than 0.1 km3 of groundwater release over 6 months. This huge and unexpected contribution increased streamflow in narrow mountainous valleys to previously unmeasured peak values. Analogously to the L’Aquila 2009 post-earthquake phenomenon, these hydrogeological changes might reflect an increase of bulk hydraulic conductivity at the aquifer scale, which would increase hydraulic heads in the discharge zones and lower them in some recharge areas. The observed changes may also be partly due to other mechanisms, such as shaking and/or squeezing effects related to intense subsidence in the core of the affected area, where effects had maximum extent, or breaching of hydraulic barriers.
Highlights
The seismic sequence recorded in central Italy in 2016–2017 included nine main events (Table 1) with moment magnitude (Mw) ≥5.0 occurring on four separate days (August 24th 2016, October 26th and 30th 2016 and January 18th 2017), as described in detail in Chiaraluce et al (2017) and ISIDe Working Group (2016)
The fractured and locally fissured carbonate nature of the aquifers outcropping in the earthquake area favors a quick co-seismic response in terms of pore pressure propagation; the observed sustained changes, which developed during several days after the main shocks, affected groundwater dynamics for several months after the seismic events
The aim of this paper is to present an overview of the effects of the 2016–2017 seismic sequence on the dynamics of groundwater flow in central Apennines, analyzing the extent of the impacted area, possible relations between tectonic environments, geological-hydrogeological setting, and groundwater changes, and providing preliminary considerations on the possible causes of the observed phenomena
Summary
The seismic sequence recorded in central Italy in 2016–2017 included nine main events (Table 1) with moment magnitude (Mw) ≥5.0 (four of which were Mw ≥ 5.5) occurring on four separate days (August 24th 2016, October 26th and 30th 2016 and January 18th 2017), as described in detail in Chiaraluce et al (2017) and ISIDe Working Group (2016). Measured responses, have become available only in the last few decades These responses include changes in water level (Leggette and Taylor 1935; Cooper et al 1965; Roeloffs 1998; Brodsky et al 2003; Roeloffs et al 2003; Lachassagne et al 2011; Shi et al 2015), temperature (Mogi et al 1989), chemical composition (Claesson et al 2004; Skelton et al 2014), stream flow (Manga et al 2003; Montgomery and Manga 2003; Manga and Rowland 2009; Muir-Wood and King 1993; Rojstaczer et al 1995), and spring attributes (Wang and Manga 2015). Understanding the origin of these hydrological and hydrogeochemical phenomena may have significant impacts on the comprehension of the occurrence of liquefaction (Cox et al 2012), water supply and quality (Gorokhovich and Fleeger 2007), underground storage (Wang et al 2013) and porepressure triggered seismicity (Brodsky et al 2003)
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