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SUMMARY:CESS Seminar : Damage signatures and imaging of crustal fault zone
 s
DTSTART:20230512T121500
DTEND:20230512T130000
DTSTAMP:20260916T085838Z
UID:d92b7f4dc82c9c6f93e1974c98981654d9b578e8368f2ebd44b72d80
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Tom Mitchell\, UCL\nAbstract\nCrustal fault zones (FZ) h
 ave been studied by field geologists\, seismologists and experimentalists 
 for decades\, and are mapped directly at the surface\, and inferred from g
 eophysics at depth. In a FZ\, fault slip is commonly hosted in a narrow fa
 ult core\, surrounded by a fracture damage zone of variable size up to 100
 s of metres in width. This damage is accrued by a combination of quasistat
 ic and coesismic processes. With increasing displacement and fault maturit
 y\, FZs increase both size and complexity\, due to overprinting of increme
 ntal damage. Fracture damage in FZs imparts a fundamental control on earth
 quakes.\nFirstly\, FZs rocks are generally more permeable than intact rock
 s\, and hence play a key role in the migration of crustal fluids. Damaged 
 rocks have reduced elastic moduli\, cohesion and yield strength resulting 
 in reduced elastic wave velocity\, causing attenuation and potentially non
 -linear wave propagation effects during ruptures. The amount and spatial v
 ariation of these reductions can directly modify rupture dynamics\, leadin
 g to the generation of slip pulses that can accelerate the transition to s
 upershear rupture. Significant reductions of velocity within a FZ results 
 in the structures trapping seismic waves that can continuously perturb str
 esses on the fault during earthquakes. At the same time\, these low veloci
 ty zones can be used to infer damage structure at depth.  Finally\, the d
 ynamic generation of damage as the rupture propagates can itself influence
  the dynamics of rupture propagation\; by increasing energy dissipation\, 
 modulating the rupture velocity and modifying the size of the earthquake\,
  changing the efficiency of weakening mechanisms such as thermal pressuris
 ation of pore fluids\, and even generating additional seismic waves. All o
 f these effects imply that a feedback exists between the damage imparted i
 mmediately after rupture propagation\, at the early stages of fault slip\,
  and the effects of that damage on subsequent ruptures dynamics.\nTo compl
 icate matters\, with increased pressure and temperature at depth\, the str
 ucture\, mechanical\, and hydraulic characteristics of a FZ are subject to
  constant change (e.g. healing and/or sealing) during the seismic cycle as
  the fault evolves. This can complicate interpreting geophysical data when
  some damage can heal rapidly\, and be subsequently invisible to many geop
 hysical techniques. Additionally\, the structure and physical properties o
 f damage depends not only on fault maturity\, but also on the scale of obs
 ervation and the types of techniques used to map and infer fault structure
  at depth.  As techniques and technology improve\, we are quantifying FZ 
 structure and damage in the field and laboratory from the kilometre to met
 re scale\, down to the nano-scale\, and combining this with advances in se
 ismic event location and high resolution tomography we have increasingly b
 etter ideas of how these structures evolve with depth. This presentation a
 ddresses the state-of-the-art of our understanding of FZ structure\, and r
 eflects on how we image and interpret fault structures at the surface and 
 below. \n\n\nShort bio\nTom Mitchell is a professor of earthquake geolog
 y and rock physics.  He did his phd in Liverpool\, postdoc fellowship in 
 Japan/Hiroshima\, Bochum/Germany\, INGV/Rome\, and been at UCL for the las
 t 9 years. He uses a combination of laboratory\, fieldwork and theoretical
  approaches in order to understand how rock and ice fractures\, deforms an
 d slides by friction.  He works on a range of topics studying the deforma
 tion of geomaterials\, from earthquakes/fault damage\, fault friction\, fl
 uid flow/ geothermal\, landslide mechanics (earth\, moon and mars)\, ice f
 racture and a variety of  other applied areas.\n\nSandwiches are offered 
 at the end of the seminar\n 
LOCATION:GC B3 30 https://plan.epfl.ch/?room==GC%20B3%2030 https://epfl.zo
 om.us/j/66461384277
STATUS:CONFIRMED
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