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CATEGORIES:Bullard Laboratories Wednesday Seminars
SUMMARY:Large cold noses and boomerang earthquakes: explor
 ing new tectonic frontiers using seafloor seismome
 ters in the Atlantic - Dr. Stephen Hicks - Imperia
 l College London
DTSTART;TZID=Europe/London:20200129T160000
DTEND;TZID=Europe/London:20200129T170000
UID:TALK137404AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/137404
DESCRIPTION:Much of our understanding of tectonic processes on
  Earth come from studies focussed in the Pacific O
 cean and along its margins. The impact of slower s
 preading rates in the Atlantic\, and its impact on
  subduction and earthquake rupture processes has r
 eceived less attention. My talk will focus on new 
 results from two UK-led ocean-bottom seismometer e
 xperiments in the Atlantic during 2016-17: The Voi
 LA experiment in the Lesser Antilles subduction zo
 ne and the PI-LAB experiment on the mid-Atlantic r
 idge.\n\nIn subduction zones\, the volume of water
  stored in the down-going plate and how it is rele
 ased into the asthenosphere wedge is key for under
 standing the mass balance of Earth’s mantle. The L
 esser Antilles subduction zone is a global end-mem
 ber for slow subduction of slow-spread\, hydrated 
 oceanic lithosphere\, which could cause variable h
 ydration and melting of the mantle. Using local ea
 rthquakes\, we have generated 3-D images of seismi
 c attenuation\, sensitive to mantle temperature an
 d fluid content. We find the asthenosphere wedge d
 oes not lie beneath the arc as expected from therm
 al-mechanical modelling. Melt may pond at the base
  of the upper plate in the back-arc with lateral m
 igration of melt through the crust towards the arc
 . The location of the hydrated core of the mantle 
 wedge agrees well with geochemical estimates of wa
 ter content from erupted magmas at the surface.\n\
 nThe simple geometry of ocean transform faults tha
 t offset spreading centres offer a rare opportunit
 y to study how fault zone friction affects earthqu
 ake rupture. We recorded a magnitude 7 earthquake 
 along the Romanche transform fault in the central 
 Atlantic on ocean-bottom seismometers. Using these
  data along with teleseismic waveforms\, we show t
 hat the rupture direction along the fault reversed
  mid-way through the earthquake. We theoretically 
 expect back-propagating rupture fronts to occur in
  mature\, low-velocity fault zones\, but we have n
 ot observed before such clear evidence of a revers
 ing rupture. This phenomenon is absent in rupture 
 simulations and unaccounted for in hazard assessme
 nts.
LOCATION:Marine/Wolfson Building lecture hall\, Bullard Lab
 s.
CONTACT:Jenny Jenkins
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