The MOLE Drilling Project: Laboratory at Depth on an Active Fault in Central Italy

Abstract

Several fundamental questions concerning: i) the geophysical and geochemical processes controlling normal faulting and earthquake ruptures during moderate-to-large seismic events and ii) the low angle normal fault paradox, still need to be fully answered. In this work we aim to present an example of low angle normal fault (Alto Tiberina Fault) located in the Northern Apennines (Italy) showing conclusive evidence of its seismic activity. This fault is a likely target of an international project: the MOLE (Multidisciplinary Observatory and Laboratory of Experiments) Drilling project. Indeed, under the auspices of the International Continental Scientific Drilling Program a workshop is being organized in Italy next spring 2008, to promote the creation of an international multidisciplinary team of scientists, to discuss the project in detail and also to prepare a full proposal for ICDP. This project wants to investigate the inner structure of normal faults in Central Italy to get physical constraints on the processes controlling faulting and earthquake mechanics. The Umbria-Marche sector of Northern Apennines offers a unique opportunity to reach a complex system of normal faults among which we selected two possible targets. 1) The active Colfiorito fault dipping about 45° toward SW which Tiberina low angle normal fault dipping 15°-25° towards ENE, which moves through a combination of aseismic creep and repeating microearthquakes. Drilling the Colfiorito active fault at a depth of about 2-3 km allows targeting the high coseismic slip patch of the 1997 earthquake M=6 seismogenic structure. Drilling the Alto Tiberina Fault at a depth of nearly 5-6 km will target a micro seismicity source. We aim to collect new original data through borehole logging and sampling and to set up a permanent observatory at depth for a multidisciplinary monitoring to characterize these active normal fault zones. This will allow to understand how such faults behave and to create more realistic models of: earthquake nucleation, seismicity pattern, stress interactions and earthquake triggering at local and regional scale. Both drilling targets present relevant technical issues that should be discussed from different points of view before selecting the starting drilling site.