Quantifying the variability and migration of active normal faulting during the Late Pleistocene-Holocene using 36Cl cosmogenic nuclide techniques
- Start date: 1 February 2016
- End date: 31 January 2021
- Primary investigator: Dr Laura Gregory
Much of the Earth is prone to damaging earthquakes. Earthquakes cannot be predicted, and the variability of earthquake occurrence makes this natural hazard difficult to anticipate. There are many fault lines that have not had an earthquake during human history, and whilst these faults are indeed active and capable of having big seismic events, they are often not realised to be a threat. This is particularly true on the continents, where the strain that results from the collision of tectonic plates is distributed such that faults occur over huge areas and in complex networks, which may interact. The interaction of faults, and how they behave on prehistoric timescales, is poorly understood due to difficulties in measuring the past fault motion.
During my fellowship, I will investigate the brittle faults that cause earthquakes on timescales longer than human history. During my fellowship, I will aim to measure how earthquake occurrence is variable over the last several tens of thousands of years. Some scientists have suggested that faults may have periods of intense earthquake activity, interspersed in quiet intervals, and I aim to quantify whether this occurs on faults in western Turkey. I will also produce models of this behaviour that will help to understand the fundamental variability of earthquakes.
Each time a fault has a large earthquake, a portion of the ground along the fault line is moved relative to the ground next to it. On extensional faults, the fault plane is uplifted and preserved for many thousands of years. As the fault plane is uplifted, it is exposed to the cosmogenic radiation that is constantly bombarding the earth's surface. This high-energy radiation produces isotopes that are otherwise not found on Earth; the result is akin to sunburn of the fault plane. The longer the plane has been exposed to cosmogenic rays, the higher the concentration of isotopes (the darker the tan). I will measure profiles of cosmogenic isotope concentrations on exposed fault planes in order to determine the history of fault exposure due to earthquakes.
My results will quantify how long periods of intense seismicity last, how frequently they occur, whether they occur on every fault in a network, and whether faults in the network switch on and off relative to one another. I will also incorporate my data into models of fault behaviour. Many models assume that earthquakes occur in regular intervals, but it is important to model what is driving irregular recurrence. The models will also help to understand the physical interaction between faults in complex networks. My research will have impact on understanding earthquake hazard both locally, in western Turkey, and worldwide.
During my fellowship whilst conducting field work in Turkey, I will conduct a ShakeOut drill in local communities, in collaboration with Prof Hasan Sozbilir. This drill is already practised in earthquake prone regions across the globe, including in the USA and Japan (www.shakeout.org). By having a mock earthquake once per year, the drill helps to increase disaster preparedness by encouraging participants to go through an earthquake checklist that includes building an earthquake-ready kit with essential survival items, practicing how to take cover during an earthquake, and determining what to do after the event. The greater impact of my research will be realised by communication of my results with scientists and policy makers alike, and efforts to increase the uptake of new understanding of fundamental earthquake behaviour.