The tectonic fault system in central Italy is responsible for notably destructive earthquakes—such as the M6.3 2009 L’Aquila and M6.2 2016 Amatrice events—and complex earthquake sequences that may last for several months or even years. The processes that control the spatial and temporal clustering of earthquakes, as in the case of the central Italy sequences, are currently only poorly understood and current models for aftershocks and earthquake triggering are incomplete. The shortcomings of current models are particularly true for central Italy, where the models inadequately explain the spatial and temporal characteristics of earthquake sequences. One proposed mechanism for fault interaction and earthquake clustering is that some faults or portions of faults slip without producing ground shaking seismic waves. Such behavior has been suggested on portions of the San Andreas fault, the North Anatolia fault, and the Cascadia subduction zone among other locations around the world. Studies of micro-earthquakes and fault rocks in central Italy indirectly support this slow aseismic slip hypothesis, but direct measurement of slow aseismic fault slip has been difficult obtain there, because specialized instrumentation is required to detect the small amplitude and slow speeds of ground motions associated with such events. Our project will deploy a network of multi-sensor instruments in shallow boreholes capable of detecting the small signals associated with slow aseismic fault slip in central Italy. The new data that we collect will provide valuable new insights into the mechanisms that control earthquakes and faulting, with important implications for earthquake hazards assessment and the physics of earthquakes and faulting.
The borehole instruments that we deploy will build on significant foreign investments in geophysical infrastructure to study aseismic Italy fault systems, taking advantage of surplus instrumentation from the NSF EarthScope Plate Boundary Observatory. The resulting data sets will address several first order questions: (1) Do aseismic faults load stress on earthquake prone faults steadily or episodically through time? (2) Does the pattern of aseismic slip correlate with the pattern of micro-seismicity on or near aseismic faults? (3) What are the spatial and temporal characteristics of aseismic fault slip, including slip magnitudes, rates, propagation directions and rates, and event durations? These questions bear directly on our understanding of fault friction and mechanics, and earthquake hazards. The data we collect will feed a burgeoning international collaboration involving US researchers and students focused on aseismic fault slip and earthquakes using central Italy as a natural laboratory. We will train a US graduate student in borehole strainmeter analysis methods. Refined understanding of aseismic slip in central Italy will bear on a long-standing debate regarding the possibility of slip on low angle normal faults in nature. Data from the borehole network and other geophysical networks will be incorporated into the Accessible Earth Study Abroad (AE) curriculum. AE is based in Orvieto, Italy, near our field central Italian field site. AE is a capstone course for students at US universities that provides a disability-accessible alternative to geology field camp and aims to increase diversity among geoscientists by making geoscience as accessible as possible to all students. Students of AE will contribute to a major international research program. The AE Program is funded independently and will run every summer indefinitely, serving approximately 8-12 US students each year.