Ground effects and hydrological changes in the Southern Apennines (Italy) in response to the 23 July 1930 earthquake (<i>M<sub>S</sub></i>=6.7)

Abstract

Abstract. The 23 July 1930 earthquake (M S =6.7) in the Southern Apennines (Italy) was a catastrophic event that produced many effects such as surface faulting, fractures, landslides, settlements, hydrological changes, variations in chemical/physical activity related to the volcanic and/or thermal zones and also acoustic and optical phenomena. It is the first great earthquake of the twentieth century that was studied, thanks to the hydrological monitoring network of the Italian Hydrographic Survey (IHS) set up from 1925 to 1929. For this earthquake we analysed the initial IHS hydrometric and pluviometric data, looking for significant anomalies in springs, water wells and mountain streams. Hydrological data relative to rivers, springs and water wells indicate that some changes can be correlated with the earthquake: a post-seismic excess discharge in some streams, pre-and coseismic decreases in stream flows and water levels in wells, pre-and post-seismic increases in discharges. The pre-and co-seismic stresses and the tectonic deformations were studied in order to find a possible model of interaction between stress state and hydrological variations. The anomalies found in this work can be considered "rebound anomalies", which are the most common precursor reported by many authors and related to increases in porosity and permeability caused by the fracturing that precedes an earthquake. An estimation of the total excess discharge (0.035 km 3 ) caused by the M S =6.7 Irpinia earthquake is consistent with the excess discharge of about 0.01 km 3 determined for the M w =6.9 Loma Prieta earthquake.

Earthquake Hydrology

“…Episodes of high discharge are correlated with seismic activity having features similar to tremor but are not correlated with large regional earthquakes (Brown et al, 2005). Data shown with circles are from the compilation in Wang and Manga (2010a) with additional data shown with squares for the M8.8 Maule earthquake of 2010 (Mohr et al, 2012), the Tasso and Tanagro river responses to the M6.7 Irpinia, Italy, earthquake of 1930 (Esposito et al, 2009), and spring responses to the M5.9 Draney Peak, the United States, earthquake of 1994 (Schuster and Murphy, 1996). Data shown with circles are from the compilation in Wang and Manga (2010a) with additional data shown with squares for the M8.8 Maule earthquake of 2010 (Mohr et al, 2012), the Tasso and Tanagro river responses to the M6.7 Irpinia, Italy, earthquake of 1930 (Esposito et al, 2009), and spring responses to the M5.9 Draney Peak, the United States, earthquake of 1994 (Schuster and Murphy, 1996).…”

Hydrological and Geochemical Changes Related to Earthquakes - Examples: Three Great Earthquakes of the XX Century in the Southern Apennines (Italy)

“…The fault plane orientation was WNW-ESE (Apennine chain trend), the fault length was 32.6 km and the depth 15 km, estimated on the basis of the equivalent ray of the major isoseismal lines (Gasperini et al, 1999). Hydrological changes were observed in the whole macroseismic field, mostly in the far field, near the main carbonate aquifers in a widespread karstic environment (Esposito et al, 2009 . Spring flow at Madonna del Carmine increased from 10 l/min to 40 l/min after the earthquake, and at Monte della Guardia increased from 5 l/min to 16 l/min at the end of August (Esposito et al, 2009).…”

“…Hydrological changes were observed in the whole macroseismic field, mostly in the far field, near the main carbonate aquifers in a widespread karstic environment (Esposito et al, 2009 . Spring flow at Madonna del Carmine increased from 10 l/min to 40 l/min after the earthquake, and at Monte della Guardia increased from 5 l/min to 16 l/min at the end of August (Esposito et al, 2009). At Solfatara, a volcanic crater in Pozzuoli (near Neaples), at a distance of about 100 km from the epicentre, variations in endogenous activity were observed for about 20 days after the earthquake.…”

The Role of Faults in Groundwater Circulation before and after Seismic Events: Insights from Tracers, Water Isotopes and Geochemistry

“…On the other hand, [26] recognized during the well-known Loma Prieta earthquake, significant hydrological changes in two basins located near field from San Andreas Fault, attributing the cause of these modifications to the formation of new fractures capable to develop novel continuous flow path or enhance existing continuous flow path. In Italy, some authors suggested different interpretations to explain groundwater modifications due to the main earthquakes occurred in the country [27][28][29][30]. As concerns the strongest earthquake occurred in Italy during the Amatrice-Norcia seismic sequence (August 2016-January 2017), some models were in fact proposed to justify the spring and river discharge change occurred in the area [11,31,32].…”