In search of fossil earthquakes: Field work in Italy's Adamello Massif

Tuesday 27 September 2016
Stephen Cox and Kathryn Hayward traversing the Lobbia Glacier to access the field site Photo credit:Giullio di Toro Inset: an example of a pseudotachylyte and injection vein formed during a fossil earthquake

In late August 2016, a group of seven geologists from universities across the UK, Italy and Australia travelled high into the mountains of Italy’s Southern Alps in search of evidence of ancient earthquakes.The field trip was led by Professor Giulio Di Toro of the University of Manchester, under his European Research Council Grant looking at the physics of earthquakes. RSES researcher Professor Stephen Cox and PhD student Kathryn Hayward are working in collaboration with these scientists to look at how the early stages of an earthquake rupture influences the size and magnitude of the subsequent event.

Of interest to the group was the Gole Larghe Fault zone; a fault with more than 1km of slip that cuts a tertiary granitic batholith exposed along the Periadriatic fault system. Thanks to global warming and the retreat of the glaciers this field area now provides some of the best preserved fault-related outcrops in the world, including a special kind of rock that forms only during earthquakes. These rocks, called pseudotachylytes, form when the rock on either side of the fault melts under the extreme pressures and temperatures associated with seismic slip.

These rocks are significant because they represent the only unequivocal evidence of ancient seismicity preserved within the rock record. Studying pseudotachylytes provides insights into the physical and chemical processes occurring during an earthquake and by combining these field observations with laboratory experiments scientists are beginning to understand the mechanisms that allow seismic events to develop. Excitingly this research has led to the discovery that these processes begin over distances of tens to hundreds of microns and within the first millisecond of slip.

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