One of the principal means of understanding upper mantle dynamics involves inferring mantle flow directions from seismic anisotropy under the assumption that the seismic fast direction (olivine a axis) parallels the regional flow direction. We demonstrate that (i) the presence of melt weakens the alignment of a axes and (ii) when melt segregates and forms networks of weak shear zones, strain pa...

refractor ambiguities are big problem in seismic refraction method especially in seismic engineering. there can be hidden subsurface geological phenomena such as hidden faults and shear zones which are not simply predicted by the travel-time graph or some geophysical methods. head wave amplitudes are used to show the resolution of refractor ambiguities and the existence of anisotropy in complex...

Earth’s upper mantle includes a 200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electromagnetic studies indicate strong heterogeneity in thinner layers underneath the p...

[1] We present modeling of the seismic delay time signature of mantle diapirs mapped in the Oman ophiolite and compare these results with those of active source seismic experiments conducted along the East Pacific Rise. To do so, we construct models of shallow-mantle, seismic anisotropy that are consistent with Oman diapirs of different size. Forward calculations of the delay time anomalies due...

Some experimental results measuring P-wave phase velocity and seismic attenuation in laboratory under dry and water-saturated conditions at ultrasonic frequencies and atmospheric pressure on sandstone samples of the Milk River Formation in the Writingon-Stone Provincial Park (WOSPP), southern Alberta, are presented and are correlated with petrophysical data obtained from these samples as clay c...

Constraints on upper crustal seismic anisotropy provide insight into the local stress orientation and structural fabric, but such constraints are scarce except in areas with dense recordings of local seismicity. We investigate directionally dependent Rayleigh wave ellipticity, or Rayleigh wave H/V (horizontal to vertical) amplitude ratios, between 8 and 20 s period across USArray to infer azimu...

Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is ...

s, 1139–1142. Grechka, V., Mateeva, A., Gentry, C., Jorgensen, P, Lopez, P. and Franco, G. [2007] Estimation of seismic anisotropy from P-wave VSP data. The Leading Edge, 26(6), 756–759. Hudson, J.A. [1981] Wave speeds and attenuation of seismic waves in materialc containing cracks. Geophysical Journal of the Royal Astronomical Society, 64, 133–150. CC02339-MA009 Seabird Exploration.indd 10...

In situ x-ray diffraction measurements of MgSiO3 were performed at high pressure and temperature similar to the conditions at Earth's core-mantle boundary. Results demonstrate that MgSiO3 perovskite transforms to a new high-pressure form with stacked SiO6-octahedral sheet structure above 125 gigapascals and 2500 kelvin (2700-kilometer depth near the base of the mantle) with an increase in densi...