Abstract
The thermal springs of Porretta are located on a seismically active area of the Northern Apennines. In 19th Century a chemist identified anomalous behaviour of the thermal waters in concomitance with local seismic events. Recent studies assessed the geochemical features of the circulating fluids (e.g., waters carry a dissolved CH4-dominated gas phase with a radiogenic signature of the helium isotopic ratio) and observed anomalous hydrologic and geochemi- cal signals possibly related to crustal strain phenomena due to local seismic events. Long-term geochemical moni- toring was carried out from 2001 to 2006 with the aim of detecting the behaviour of the circulating fluids possibly coinciding with seismic activity. The collected data reveal a sensitivity of the thermal waters to the activity of the main fault crossing the village of Porretta and identify a «seismogenic» structure crossing the village.
Highlights
The thermal springs of Porretta are located in the Northern Apennines over an area crossed by several tectonic lineaments
Following tales and visual observations reported by local inhabitants, we found out that the thermal springs of Porretta Terme have undergone changes coinciding with seismic activity
The discharged thermal waters are fed by meteoric waters which reached saturation with carbonatic rocks, mixed to brines coming from Pliocene sediments
Summary
The thermal springs of Porretta are located in the Northern Apennines over an area crossed by several tectonic lineaments (fig. 1). In particular Capponi (1608) noted that «after five local seismic events water flow-rate increased up to four times more than. He observed that in concomitance with local seismic events a water level decrease in a local well accompanied a flow rate increase of the thermal springs. After a local Mw= 5.3 seismic event in 2003 (Seismic Bulletin, 2007) whose epicentre was located close to the village of Monghidoro about 25 km to the East of Porretta Terme, significant anomalies in temperature, flow rate and bubbling gas emissions were recorded both by visual observations and direct measurements. To better understand possible relations among local seismicity and hydrogeochemical patterns of Porretta thermal springs a geochemical prospection and a continuous monitoring program were carried out. This paper deals with the main results obtained from the collected geochemical data focussing on the relationship between fluids and tectonic structures
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