Earth analogue material

 
 

My postdoctoral research at the Earthquake Research Institute (ERI) of the University of Tokyo was an experimental study of anelasticity in polycrystalline materials. The PI for the project was Dr. Yasuko Takei. The goal of the research was to clarify the influences of temperature, grain size and partial melt on seismic attenuation. With the custom-fabricated apparatus (left top), we measured the attenuation, Young’s modulus, and viscosity of borneol, a crystalline organic material that has been found to be a good analogue to mantle rock. We found that data taken at various temperatures and grain sizes could be scaled by the Maxwell frequency (the ratio of the unrelaxed modulus to viscosity) to obtain a master curve. We found that the attenuation data from previous studies on olivine-dominated samples also collapse to a single master curve when scaled by the Maxwell frequency. Thus one exciting result from the study was that the anelasticy of polycrystalline material is Universal. With this scaling, we can extrapolate laboratory results to velocity and attenuation of seismic shear waves.


Additionally we combined borneol with a second organic, diphenylamine, to take advantage of eutectic phase relations to obtain partial melting at conditions just above room temperature. We measure the anelasticity and viscosity of partially molten samples as a function of melt fraction. We found that even a small quantity of melt (melt fraction = 0.0025) greatly increased attenuation and dispersion and decreased the viscosity. The large drop in viscosity due to a small amount of melt would manifest itself as a perturbation in seismic velocity on the order of 1-2%, which may be detectible in seismic observations. Furthermore, the similitude that was observed in melt-free samples was also observed in these melt-bearing samples, so that all data--regardless of grain size, temperature, sample type (olivine vs. organic), loading type (shear vs. longitudinal), composition, or percent of partial melt--collapse to a single master attenuation curve when scaled by the Maxwell frequency. This finding provides insight into the relaxation processes occurring in polycrystalline materials at the grain scale.


 

Photos (cntr clockwise from rt top)

  1. 1.wearing a traditional yukata at the summer work party

  2. 2.the microstructure of borneol-diphenylamine

  3. 3.custom-fabricated attenuation apparatus

  4. 4.making fine-grained samples with a bench press (in a yukata)

About Me

Experimental studies on mantle analogue