Seismic Activity Along a Low-Angle Normal Fault: The Case Study of the Alto Tiberina Fault (Northern Apennines, Italy).

Monday, 15 December 2014: 8:30 AM
Luisa Valoroso, Lauro Chiaraluce and Raffaele Di Stefano, INGV National Institute of Geophysics and Volcanology, Rome, Italy
Crustal faults are complex systems whose mechanical conditions and physical properties vary in space and time. The availability of long time series of high-resolution multidisciplinary data is a fundamental requirement to understand the multi-scale physical processes controlling faulting and earthquake generation processes. A crucial step for the seismological community is the availability of high-resolution catalogues of accurate earthquake locations describing the long-term brittle response of the fault activity.

We report on the seismicity recorded in a sector of the Northern Apennines undergoing active extension and where a set of high-angle normal faults is detached by the Alto Tiberina low-angle normal fault (ATF). From 2010, this area hosts a research infrastructure (the Alto Tiberina Near Fault Observatory, TABOO), consisting of a dense array of multi-sensor stations, devoted to studying the earthquakes preparatory phase and the fast and slow deformation processes along the ATF fault system.

We show the location of about 30k low-magnitude earthquakes recorded during the past 4 years (2010-2014) showing a completeness magnitude of the catalogue of ML0.5. Data have been analyzed by combining an automatic picking procedure for P and S waves, together with cross-correlation and double-difference location methods.

The seismicity pattern shows an almost constant and high rate of seismic release along the ATF plane (r = 24.30eāˆ’04 eqks/day*km2) with clusters of similar events identified all along the fault plane. On the contrary a long series of low magnitude seismic sequences (Mmax 4.0) activated minor synthetic and antithetic normal faults segments (4ā€“5 km long) located in the main fault hanging-wall. The geometry of the fault segments described by the seismicity distribution is cinematically consistent with the focal mechanisms solutions.