In order to study the stability field of GeO2 under high pressure at room temperature, an in situ observation was made by using a diamond anvil pressure cell, an optical microscope and a high speed VTR. At about 6.5GPa, a transparent single-crystal of α-quartz type GeO2 quickly changed to a translucent material which was found to be X-ray amorphous. The loss of transparency induced by the transformation is attributed to the pulverization due to the large volume change (approximately 10%), which causes the increase of refractive index and introduces the imperfection into the single-crystal.
We perform iterative waveform inversion for laterally heterogeneous upper mantle structure using a new method for computing synthetic seismograms and their partial derivatives. The shorter wavelength lateral heterogeneity of our model differs significantly from previous models in the deeper part of the upper mantle. The better variance reduction attained by our model suggests that it is a more accurate model of upper mantle structure.