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SUMMARY:Slip rate variability: Quantifying the past to understand the pres
 ent - Laura Gregory - University of Leeds
DTSTART:20200311T160000Z
DTEND:20200311T170000Z
UID:TALK137422@talks.cam.ac.uk
CONTACT:Jenny Jenkins
DESCRIPTION:In an ideal world\, earthquakes would occur at regular interva
 ls such that information on the rate and typical size of events could be u
 sed to make accurate forecasts of the future likelihood of earthquakes. Ho
 wever\, examples from different fault systems suggest that the rate of ear
 thquake occurrence varies more than would be expected using a classic mode
 l of stress accumulation.\nTo explore this problem\, I will show examples 
 of fault behaviour from a range of scales in time and space. Central Italy
  is an excellent location to study active tectonics\, where mid-magnitude 
 earthquakes occur as a result of continental extension. This activity has 
 produced numerous limestone bedrock fault scarps\, preserved since the dem
 ise of the Last Glacial Maximum (about 10-20 kyr). Each earthquake exposes
  the fault scarp to cosmic radiation\, which produces cosmogenic chlorine-
 36 in-situ at the Earth’s surface and down to a few meters depth. The co
 ncentration of 36Cl measured along the fault scarp can be used to infer pa
 st slip histories\, which show that faults experience highly variable eart
 hquake activity\, with periods of greater intensity lasting probably thous
 ands of years\, separated by times of quiescence. I will place this slip r
 ate variability in the context of the most recent sequence to affect the r
 egion\, in 2016\, which exhibited fault complexity at shorter timescales. 
 \nFinally\, in order to further understand the mechanics of faulting\, we 
 will look to the rock record of earthquakes recorded in faulting microstru
 ctures from faults that have been characterised by cosmogenic analyses. A 
 key part of the earthquake cycle is the transition from very weak during t
 he earthquake\, to strong enough to accrue stress that ultimately builds t
 o a subsequent earthquake. These observations give insight into the rheolo
 gy of faults throughout the earthquake cycle\, which is crucial for unders
 tanding how the state of stress evolves through time\, and may help to exp
 lain non-uniform behaviour over multiple earthquake cycles.	\nSuggested re
 ferences:\nCowie\, P. A.\, Roberts\, G. P.\, Bull\, J. M.\, and Visini\, F
 .\, 2012\, Relationships between fault geometry\, slip rate variability an
 d earthquake recurrence in extensional settings: Geophysical Journal Inter
 national\, v 189\, p 143-160.\nCowie\, P. A.\, et al.\, 2017\, Orogen-scal
 e uplift in the central Italian Apennines drives episodic behaviour of ear
 thquake faults: Scientific Reports\, v. 7:44858.\nWalters\, R. J.\, et al.
 \, 2018\, Dual control of fault intersections on stop-start rupture in the
  2016 Central Italy seismic sequence: Earth and Planetary Science Letters\
 , v. 500\, p. 1-14.
LOCATION:Marine/Wolfson Building lecture hall\, Bullard Labs.
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