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SUMMARY:Effect of partial melting on seismic velocity and attenuation: Pol
 ycrystal anelasticity at near-solidus temperatures - Yasuko Takei (Univers
 ity of Tokyo)
DTSTART:20160608T103000Z
DTEND:20160608T113000Z
UID:TALK66389@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:<span>Co-author: Hatsuki Yamauchi (ERI\, Univ. of Tokyo)  <br>
 </span> <span><br>Seismic low velocity regions have been detected around t
 he volcanic source  regions in the upper mantle\, where partial melting is
  expected to occur.  However\, temperature of these regions is\, for the m
 ost part\, below the solidus  temperature of dry mantle peridotite. This s
 uggests that seismic wave velocity  is significantly reduced in the absenc
 e of melt or in the presence of a very  small amount of melt stabilized by
  volatiles. Effects of partial melting on the  seismic velocity and attenu
 ation have long been studied within the framework of  the direct effect of
  the melt phase\, such as poroelastic effect. However\, the  direct effect
  is small for small melt fraction\, and is difficult to explain the  relat
 ively large velocity reduction observed in these regions. Rock  anelastici
 ty\, which can cause low velocity by grain boundary sliding even  without 
 the melt phase\, has been considered as a key to solve this problem.  Howe
 ver\, due to the difficulty of high temperature experiment\, we have had a
   limited understanding of rock anelasticity at the seismic frequencies. W
 e  therefore measured anelasticity by using a rock analogue (organic polyc
 rystals).  Elasticity\, anelasticity\, and viscosity were measured continu
 ously from below to  above the solidus temperature and the mechanical beha
 vior at near solidus  temperatures was clarified over a broad frequency ra
 nge. The obtained data  predict that a steep reduction of seismic shear wa
 ve velocity occurs just below  the solidus temperature in the absence of m
 elt. Our data also show that the  seismic properties are not sensitive to 
 the existence or nonexistence of a very  small amount of melt\, whereas mo
 re than 1 percent melt can cause additional  velocity reduction depending 
 on the melt fraction.&nbsp\;</span>
LOCATION:Seminar Room 1\, Newton Institute
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