John Bedford, University of Liverpool

Geophysical evidence suggests that some faults are frictionally strong, in agreement with laboratory measurements of quasi-static frictional strength (μ ≈ 0.6-0.8) for many crustal materials; whereas others studies have found that some faults are weak when compared to laboratory friction values (μ < 0.5). It has also been well documented that fault materials undergo a significant dynamic reduction in frictional strength when the sliding velocity accelerates to earthquake slip rates (on the order of meters per second). In this talk I will review our current understanding of fault strength evolution during the seismic cycle, then I will present results from two recent laboratory studies where we attempt to elucidate some of the dominant controls on fault strength both before and after an earthquake has occurred. Firstly, I will present results from a study where we investigate how geological heterogeneity in fault zones affects fault strength and stability; we find that heterogeneous faults are considerably weaker and more frictionally unstable than compositionally identical faults with an initially homogeneous structure. Then I will present results from some high-velocity friction experiments where we investigate how faults recover their strength after experiencing dynamic weakening during a seismic slip event. Our findings show that fault strength recovery (healing) occurs rapidly after high-velocity slip, which has important implications for our understanding of rupture dynamics and earthquake recurrence.

Short biography
John Bedford completed his degree in Earth Sciences at the University of Glasgow (UK), before moving on to the University of Liverpool where he completed a PhD in experimental rock mechanics. After that, he continued in Liverpool as a postdoc, investigating the frictional properties of fault zones; and then, in 2020, he moved to Japan to work as a postdoctoral fellow at JAMSTEC (Japan Agency for Marine-Earth Science and Technology), where he worked in the rock mechanics laboratory investigating fault friction at high slip velocities. In 2023, John recently started a postdoc position back in the UK as part of the SeisGreen project, a large collaborative project between Imperial College and the Universities of Liverpool, Manchester, Bristol and Leeds to investigate induced seismicity caused by subsurface fluid injection associated with the green transition.