The Apennines, a 1500 kilometer long mountain range in Italy, form a tectonically active boundary between the Eurasian and the Adriatic plates, making Italy prone for earthquakes. Recently, the earthquakes in L’Aquila (2009) and the earthquake sequence in Amatrice-Norcia-Visso (2016-2017) are remembered for their devastating destruction and numerous fatalities.
Area of specific geological interest
From the many faults in the Apennines, the low-angle normal Alto-Tiberina Fault (ATF) in the northern part of the mountains is of particular interest. The fault creeps at comparatively shallow depths and both seismic and aseismic slip can be observed on a single fault. Understanding the underlying physics has implications for seismic hazard classification and risk assessment around the world.
Drilling project STAR started
With this goal in mind, the STAR project (A Strainmeter Array Along the Alto Tiberina Fault System, Central Italy), funded by the International Continental Scientific Drilling Program ICDP and the Istituto Nazionale di Geofisica e Vulcanologia INGV, began at the end of September. International partner institutions from Italy, the USA and Germany are working together on the survey of the ATF near the town of Gubbio (Umbria). In the meantime, the STAR team has drilled the first of a total of six 80 to 160 metres deep boreholes, which are planned at intervals of several kilometres. The boreholes do not reach down into the fault itself, but will provide relevant data from the zone above - over a period of many years: For long-term geophysical monitoring, they will be equipped with strain- and seismometers.
Special features of the Alto Tiberina Fault
At the Alto Tiberina Fault (ATF), rock layers with only a slight inclination lie on top of each other. They actually hardly slip at all, so that only low earthquake activity would be expected. Nevertheless, the opposite is observed at times: Gubbio was hit by an Mw 5.6 earthquake in 1984. This contradictory behaviour is sometimes referred to as the "low angle normal fault paradox ". Furthermore, repeated earthquakes, GPS time series and other data provide clear evidence that the ATF fault creeps at relatively shallow depths. This means that the rock layers move past each other very slowly without initially causing large shocks.
In the focus of research
The shallow depth makes the ATF an easily accessible object of study to answer fundamental questions about geophysical and geochemical processes that control normal faulting and earthquake ruptures during medium to large seismic events. The focus here: the interplay of various geophysical and geological phenomena of subsurface activity - creep, slow slip, stress build-up, dynamic earthquake rupture and tectonic faulting. The researchers want to find out e.g. whether the creep is occurring in steady-state or episodically, whether creep coincides or is adjacent to repeating earthquakes, and how creep relates to seismic swarms.
Several scientists from the GFZ are involved in the STAR project, including:
Dr. Simona Pierdominici (Interpretation of borehole data: What information can be gained from logging the borehole, for example about the nature of the rock drilled through?)
Dr. Thomas Wiersberg (Gas geochemical investigations during drilling: At which depth in the drilled-through rock are which gases released?)
Dr. Patricia Martínez-Garzón (Analysis of the slow deformation detected with borehole strain gauges along the ATF and its interaction with potentially dangerous earthquakes)
Prof. Dr. Marco Bohnhoff (Project leader from the GFZ side)
Prof. Dr. Marco Bohnhoff
Head Section Geomechanics and Scientific Drilling
Helmholtz Centre Potsdam
GFZ German Research Centre for Geosciences
Phone: +49 331 288-1327