Spatio-temporal variations of slip on active norma faults in central and southern mainland Greece

Understanding how earthquakes occur in space and time has been a complex problem. Two key problems in earthquake forecasting are unpredictable earthquake recurrence times and unpredictable size of earthquakes. The lack of understanding of these issues have resulted in destructive consequences when earthquakes do occur.

The problems may remain unsolvable but we can start to improve the understanding of seismic hazard by investigating several factors, such as, fault location, geometry, kinematics, multi-millennia slip-rate histories and strain-rate of fault arrays. The factors are important and should be considered in assessing seismic hazard as they address the following. (a) Fault geometry may relate to rupture kinematics associated with earthquakes. Analysis of the fault geometry and kinematics may help describe the style of ruptures and potentially explain how earthquakes migrate. (b) multi-millennia slip-rate histories analyse time periods long enough to identify multiple earthquakes on faults and identify patterns; clustering and quiescence. (c) Strain-rates of fault arrays reveal how the total combined earthquakes or strain over the multi-millennia timescale is distributed across regions.

Greece is a perfect natural laboratory for studying these factors as the country contains a complex network of active faults. The combination of large structures in the form of the Hellenic trench subduction zone and the North Anatolian strike-slip fault have resulted in early stage rifting processes which have produced several differently orientated normal fault arrays. These normal faults frequently show activity in the form of earthquakes which are felt as the crust stretches with destructive earthquakes (Ms ~ 6.0 or greater) occurring approximately once a decade.

The overall aim of the PhD project is to investigate different spatial scales from single faults to entire fault arrays whilst incorporating temporal aspects to help reveal the importance of millennia-scale earthquake clustering and quiescence. This will be undertaken by assessing the factors mentioned above; fault location; geometry; kinematics; multi-millennia slip-rate histories; and strain-rate of fault arrays. Generally, the project will include analysis of a specific example of a historic earthquake sequence and the production of a suite of strain-rate maps for multiple fault arrays. (Part 1) Initially, a local spatial investigation of two faults, which have ruptured during a historic earthquake sequence, will be undertaken to analyse the role that fault geometry may have on controlling the rupture style. (Part 2) An accompanying temporal study will be undertaken in the form of 36Cl cosmogenic nuclide-derived fault slip histories of the two faults which will be compared in an attempt to understand how or if the proximal faults relate in terms of their slip histories. (Part 3) The strain-rate mapping will be a temporal and spatial investigation at the scales of entire fault arrays with the aim of displaying the regional distributions of Holocene earthquake activity. The Holocene strain-rates will also be compared to published historical strain-rates to show that seismic hazard varies spatially on different time scales.

Studying the temporal and spatial activity of faults will have an important impact on improving seismic hazard analysis and refining earthquake forecasting. Greece is a suitable location for studying faulting due to the complex tectonic setting and frequent earthquake activity. Greek faults have been studied, however, more extensive field data are required in order to help constrain the factors (fault location, geometry, kinematics, multi-millenia slip-rate histories and strain-rate of fault arrays) in central mainland Greece and therefore, improve the understanding of tectonic processes and seismic hazard.