Unusual geological phenomena in the Emilia-Romagna plain (Italy): gas emissions from wells and the ground, hot water wells, geomorphological variations. A review and an update of documented reports

Fifty-two unusual geological phenomena (up to November 2015) were reported during a three-year observation period after the seismic swarm that occurred in Emilia in May-June 2012. Here we show and discuss for the first time the data collected directly from wells with apparently abnormal temperatures. Most of the abnormal temperatures occurred in the areas struck by earthquakes, but others were located in the urban area of Bologna and in the eastern sector of the Ferrara province. No relationship between the temperature data and the earthquakes was observed. The Italian oil company AGIP (now ENI) has recorded a large number of hydrocarbon surface phenomena in Emilia-Romagna since the early decades of the 20th century. The phenomena were located both in the Po Plain and in the Apennines. This database was recently provided by ENI and, for the first time, utilized for research purposes following the 2012 Emilia seismic sequence. The emissions observed are due to the presence of methane gas mixed with groundwater, resulting from the decomposition of organic matter present in proximity to tapped aquifers, or gas rising from greater depths along tectonic discontinuities. Similar to the findings involving the well temperatures, no significant relationship was found between the geographic distribution of the hydrocarbon emissions and the earthquakes. Ground-shaking phenomena, however, have sometimes induced temporary increases in the gas flow rate.