Measuring the earthquake deformation cycle on normal faults, with InSAR and cosmogenic chlorine-36 analysis

The earthquake deformation cycle on normal faults is relatively under-studied, in comparison to much larger strike-slip faults. Improved observations and interpretations of normal fault structure and behaviour over multiple earthquake cycles will aid understanding of their seismic hazard. I combine geodetic observations over three decades with geological observations over millennia to interpret the behaviour of normal faults.

In Chapter 3, I present Sentinel-1 InSAR time-series for 3 - 7 years of postseismic observations following four moderate-sized normal faulting earthquakes in Peru, Tibet and Greece that occurred between 2016 - 2021. All four case studies show significant postseismic surface displacement, with up to 100 - 850 mm of horizontal and up to 70 - 210 mm of vertical displacement across the fault. I model the surface displacement time-series as either an exponential or logarithmic function and suggest that afterslip is the dominant postseismic process, as the rapid decay of the displacement time-series is fit well by a logarithmic decay function.

In Chapter 4, I present the longest-ever displacement time-series of postseismic deformation following a normal-faulting earthquake, by combining observations from ERS, Envisat and Sentinel-1 for 30 years following the 1995 Mw 6.5 Grevena earthquake. Afterslip is the dominant process near the fault, and there is a continuous decay in the amount of postseismic deformation over this time. For all case studies in Chapters 3 & 4, the postseismic deformation was still ongoing in 2024.

In Chapter 6, I measure the chlorine-36 concentration in samples from the bedrock limestone fault scarp of the Esen Fault, Turkiye. I combine these observations with Bayesian Monte Carlo Markov Chain modelling to interpret the long-term slip history of the fault. I suggest that the Esen Fault has a near-constant fault slip rate of 2 - 3 mm/yr over the past 10,000 years, and experienced a major slip event of 240 cm about 1 kyr ago. This is equivalent to a Mw 7.0 earthquake and demonstrates a previously uncharacterised hazard.