Abstract

Observations of field exposures of active faults and historical/instrumental records of earthquakes all point towards earthquakes being complex phenomena, which makes quantifying probabilistic seismic hazard a challenge. Furthermore, the behaviour of an individual fault or fault system may vary depending on the timescales over which we observe and collect data.

In this talk, I will present a range of studies from my research, spanning timescales of observations of years to millions of years. Most of my work focusses on extensional systems in the Mediterranean, particularly central Italy and the Gulf of Corinth – having been inspired during my Cambridge undergraduate 4th year fieldtrip to Greece!

Central Italy has a 700 year record of devastating earthquakes, including most recently the 2016 Amatrice earthquake sequence. This sequence was fascinating for several reasons, including its spatial and temporal pattern, the associated surface ruptures and the fact it occurred on a fault that was a “debated seismogenic source” that had not ruptured in ~2-4kyr. Using 36Cl cosmogenic dating on the causative fault, we have shown that the slip rate of this fault (as well as other nearby faults) is variable over the Holocene (15±3kyrs), and we attempt to understand the physical mechanism that is controlling the observed slip rate variations.

The extend our timescales of observation beyond field-based studies, we have begun to use 3D seismic reflection surveys from inactive rift systems to explore how slip rates vary over millions of years, on both individual faults and across fault networks. This work is part of my UKRI Future Leaders Fellowship project Quake4D, which aims to combine geological observations with physics-based numerical modelling to explore a wider range of earthquake scenarios than would be possible using observations alone.

From the range of timescales studied, a common theme is that fault slip rates are variable. This raises important questions about the use of fault slip rates, whether derived from geology or geodesy, in fault-based probabilistic seismic hazard assessment.