Velocity gradient

About: Velocity gradient is a research topic. Over the lifetime, 3013 publications have been published within this topic receiving 77120 citations.

Polarization tomography for P wave velocity structure in southern California

Abstract: We develop a tomographic inversion method that uses teleseismic P wave polarization data to obtain velocity structure. Polarization inversion has some intrinsic advantages over travel time inversion: It is not influenced by source location and origin time errors; it is not sensitive to deep mantle velocity structure and can be used iteratively to improve the tomographic result. Polarization inversion is more sensitive to near-station velocity structure and to velocity gradient and is complementary to travel time inversion in this sense. The method is applied to California Institute of Technology-U.S. Geological Servey southern California array data. The result is generally consistent with previous work and also reveals that the high-velocity feature beneath the Transverse Ranges is bounded between 40 and 200 km depths and possibly has a second small piece at about 300 km depth. The slow velocity anomaly under the Salt on Trough is limited to shallow depths, less than about 60 km.

Global-in-time Hölder continuity of the velocity gradients for fluids with shear-dependent viscosities

Abstract: For an evolutionary nonlinear fluid model characterized by the viscosity being a decreasing function of the modulus of the symmetric velocity gradient we establish the global-in-time existence of the solution with the Holder continuous velocity gradients. Such a solution is unique in the class of weak solutions. We deal with the two dimensional space periodic problem.

Pulsatile Flow of a Chemically-Reacting Nonlinear Fluid

Abstract: Many complex biological systems such as blood and polymeric materials can at times be approximated as single constituent homogeneous fluids whose properties can change due to the chemical reactions that take place. For instance, the viscosity of such fluids could change both due to the chemical reactions and the flow. Here, we investigate the pulsatile flow of a chemically-reacting fluid whose viscosity depends on the concentration of a species (constituent) that is governed by a convection-reaction-diffusion equation and the velocity gradient, which can thicken or thin the fluid. We study the competition between the chemical reaction and the kinematics in determining the response of the fluid.

A baseline for upper crustal velocity variations along the East Pacific Rise at 13°N

Abstract: A wide aperture profile of the East Pacific Rise at 13°N provides data necessary to make a high-resolution seismic velocity profile of the uppermost crust along a 52-km segment of ridge crest. Automated and objective processing steps, including τ − p analysis and waveform inversion, allow the construction of models in a consistent way so that comparisons are meaningful. A continuous profile is synthesized from 70 independent one-dimensional models spaced at 750-m intervals along the ridge. The resulting seismic velocity structure of the top 500 m of crust is remarkable in its lack of variability. The main features are a thin low-velocity layer 2 A at the top with a steep gradient to layer 2B. The seafloor velocity is nearly constant at 2.45 km/s ±3% along the entire ridge. The velocity at the top of layer 2B is 5.0 km/s ±10%. The depth to the 4 km/s isovelocity contour within layer 2A is 130±20 m from 13°to 13°20′N, north of which it increases to 180 m. The increase in thickness is coincident with a deviation from axial linearity (DEVAL) noted by both a slight change in axis depth and orientation and in geochemistry. The waveform inversion, providing more details plus velocity gradient information, shows a layer 2A with about 80 m of constant-velocity material underlain by 150 m of high velocity gradient material, putting the base of layer 2A at approximately 230 m depth south of 13°20′N and about 50 m thicker north of the DEVAL. The overall lack of variability, combined with other recent measurements of layer 2A thickness along and near the axis, indicates that the thickness of volcanic extrusives is controlled not by levels of volcanic productivity, but the dynamics of emplacement. The homogeneity along axis also provides a baseline of inherent variability in crustal structure of about 10% against which other observed variations in similar regimes can be compared.

Two-layer model for open channel flow with submerged flexible vegetation

Abstract: A two-layer model for predicting the vertical distribution of stream-wise velocity in open channel flow with submerged flexible vegetation is proposed Using the predicted deflection height of the flexible vegetation determined via the large-deflection cantilever beam theory, the flow is vertically separated into a bottom vegetation layer and an upper free water layer, and corresponding momentum equations for each layer are formulated In the bottom vegetation layer, the resistance caused by the deflected plants is calculated accounting for plant bending rather than adopting the existing resistance formula for erect rigid vegetation For the upper free water layer, a new type of polynomial velocity distribution is suggested instead of the traditional logarithmic velocity distribution to obtain a zero velocity gradient at the water surface To validate the proposed model, the published experimental data are employed