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SUMMARY:Earthquakes\, Stress Drops and the Strength of Faults - Simon Lamb
 \, Victoria University of Wellington\, New Zealand
DTSTART:20241009T130000Z
DTEND:20241009T140000Z
UID:TALK222055@talks.cam.ac.uk
CONTACT:Adriano Gualandi
DESCRIPTION:Natural earthquakes are usually a sign of rocks breaking along
  faults\, relieving stress in the outer part of the Earth. In this talk\, 
 I will discuss ideas about the links between earthquakes and the strength 
 and frictional behaviour of these faults. The classical view is that earth
 quakes only contain information about the change in strength of a fault du
 ring the rupture\, which could be large or small compared to the ambient d
 eviatoric stress levels. However\, it is now widely thought that earthquak
 es are due to dynamical weakening of the fault during the early stages of 
 its failure and slip\, with the strength dropping to negligible values at 
 seismic slip velocities. In this case\, the change in strength of the faul
 t during rupture is also a measure of the total magnitude of the driving s
 tresses. I show that measured stress drops during earthquakes are typicall
 y very low\, with a log normal distribution mainly in the range 1 – 10 M
 Pa. This distribution is essentially the same regardless of whether earthq
 uakes are grouped by magnitude\, focal mechanism\, or depths\, providing t
 he basis for the well-established earthquake scaling laws.  I argue that t
 his creates a problem for dynamical weakening models\, because it requires
  either very low ambient deviatoric stresses in the seismogenic parts of t
 he crust\, and hence weak rocks\, or very prescriptive rupture behaviour i
 n which normal stress has a confounding effect\, and hence may not be suff
 iciently general. This raises the question of whether or not laboratory-sc
 ale experiments on dynamical friction are a good description of much large
 r scale rupture behaviour in natural earthquakes.
LOCATION:Wolfson Lecture Theatre
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