The Emilia Romagna 2012 seismic sequence featured 7 events above magnitude 5, the biggest of which took place on May 20, 2012 (M L =5.9) and on May 29, 2012 (M L =5.8). The main shock nucleated at a depth of 6.3 km, along a 15 km EW tr ending thrust fault, dipping south, while the May 29, 2012 event took place along an adjacent fault segment, 12 km to the west of the main shock, and at a greater depth (10.2 km). Both events were accompanied by remarkable changes in some water wel ls that belong to the regional monitoring network. The avai lable water level time series describe a clear peak (positive a t all the affected wells), whose shape and magnitude change with well depth and with the distance from the epicenter. In this work we focus on the response of the shallow aquifers to the seismic activity. We apply an unsaturated porous media flow model to stu dy the evolution of pore pressure through the heterogeneou s aquifer system. Our model incorporates the available inform ation on the subsurface stratigraphy and aquifer properties, and describes the water table elevation as a function of pore pressur e. The seismic events give rise to instantaneous pore pressure flu ctuations, which gradually vanish with time. The magnitude of such fluctuations will be based on an estimate of the st ress changes caused by the main seismic events, whose sources ar e inverted from observed coseismic displacements. Numerical re sults will be compared with observed water level data to infer aq uifer properties and compare the performance of different parametrization of the seismic events.
Modeling of aquifer behavior during the 2012 Emilia Romagna seismic sequence
NESPOLI, MASSIMO;ANDERLINI, LETIZIA;GUALANDI, ADRIANO;BELARDINELLI, MARIA ELINA;BONAFEDE, MAURIZIO;
2013
Abstract
The Emilia Romagna 2012 seismic sequence featured 7 events above magnitude 5, the biggest of which took place on May 20, 2012 (M L =5.9) and on May 29, 2012 (M L =5.8). The main shock nucleated at a depth of 6.3 km, along a 15 km EW tr ending thrust fault, dipping south, while the May 29, 2012 event took place along an adjacent fault segment, 12 km to the west of the main shock, and at a greater depth (10.2 km). Both events were accompanied by remarkable changes in some water wel ls that belong to the regional monitoring network. The avai lable water level time series describe a clear peak (positive a t all the affected wells), whose shape and magnitude change with well depth and with the distance from the epicenter. In this work we focus on the response of the shallow aquifers to the seismic activity. We apply an unsaturated porous media flow model to stu dy the evolution of pore pressure through the heterogeneou s aquifer system. Our model incorporates the available inform ation on the subsurface stratigraphy and aquifer properties, and describes the water table elevation as a function of pore pressur e. The seismic events give rise to instantaneous pore pressure flu ctuations, which gradually vanish with time. The magnitude of such fluctuations will be based on an estimate of the st ress changes caused by the main seismic events, whose sources ar e inverted from observed coseismic displacements. Numerical re sults will be compared with observed water level data to infer aq uifer properties and compare the performance of different parametrization of the seismic events.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
