Mutually consistent estimates of upper mantle composition from seismic velocity contrasts at 400 km depth

1993 ◽  
Vol 141 (1) ◽  
pp. 101-109 ◽  
Author(s):  
Craig R. Bina
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Mantle Composition ◽  
Seismic Velocity Contrasts

Channel waves in cross‐borehole data

Geophysics ◽  
1992 ◽  
Vol 57 (2) ◽  
pp. 334-342 ◽  
Author(s):  
Larry R. Lines ◽  
Kenneth R. Kelly ◽  
John Queen
Keyword(s):  
Seismic Velocity ◽  
Test Facility ◽  
Equation Modeling ◽  
Borehole Data ◽  
Geological Information ◽  
Channel Wave ◽  
First Arrival ◽  
Borehole Seismic ◽  
Seismic Velocity Contrasts ◽  
Ray Bending

Layered geological formations with large seismic velocity contrasts can effectively create channel waves in cross‐borehole seismic data. The existence of channel waves for such waveguides can be confirmed by ray tracing, wave equation modeling, and modal analysis. Channel wave arrivals are identified in cross‐borehole data recorded at Conoco’s Newkirk test facility. For these data, where velocity contrasts are about 2 to 1, tomography based on first arrival traveltimes, is limited due to problems with extreme ray bending and seismic shadow zones. However, it may be possible to extract geological information using channel wave information. The seismometer differencing method appears to be a promising approach for detecting waveguide boundaries by use of cross‐borehole data.

scholarly journals Antarctic Upper Mantle Rheology

2021 ◽  
pp. M56-2020-19
Author(s):  
E. R. Ivins ◽  
W. van der Wal ◽  
D. A. Wiens ◽  
A. J. Lloyd ◽  
L. Caron
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Effective Viscosity ◽  
Seismic Velocity ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Velocity Model ◽  
Mantle Flow ◽  
S Wave ◽  
Velocity Changes

AbstractThe Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response time scale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modeling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and paleo sea-level investigations of Antarctica provide quantitative ways of independently assessing the three-dimensional mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

Quaternary sodic and potassic intraplate volcanism in northeast China controlled by the underlying heterogeneous lithospheric structures

Geology ◽  
2021 ◽  
Author(s):  
Xingli Fan ◽  
Qi-Fu Chen ◽  
Yinshuang Ai ◽  
Ling Chen ◽  
Mingming Jiang ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Northeast China ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Subcontinental Lithospheric Mantle ◽  
Seismic Velocities ◽  
S Wave ◽  
Crust And Upper Mantle ◽  
Potassic Volcanism

The origin and mantle dynamics of the Quaternary intraplate sodic and potassic volcanism in northeast China have long been intensely debated. We present a high-resolution, three-dimensional (3-D) crust and upper-mantle S-wave velocity (Vs) model of northeast China by combining ambient noise and earthquake two-plane wave tomography based on unprecedented regional dense seismic arrays. Our seismic images highlight a strong correlation between the basalt geochemistry and upper-mantle seismic velocity structure: Sodic volcanoes are all characterized by prominent low seismic velocities in the uppermost mantle, while potassic volcanoes still possess a normal but thin upper-mantle “lid” depicted by high seismic velocities. Combined with previous petrological and geochemical research findings, we propose that the rarely erupted Quaternary potassic volcanism in northeast China results from the interaction between asthenospheric low-degree melts and the overlying subcontinental lithospheric mantle. In contrast, the more widespread Quaternary sodic volcanism in this region is predominantly sourced from the upwelling asthenosphere without significant overprinting from the subcontinental lithospheric mantle.

scholarly journals Seismic Velocity Structure in the Crust and Upper Mantle beneath Northern Japan.

1994 ◽  
Vol 42 (4) ◽  
pp. 269-301 ◽  
Author(s):  
Hiroki Miyamachi ◽  
Minoru Kasahara ◽  
Sadaomi Suzuki ◽  
Kazuo Tanaka ◽  
Akira Hasegawa
Keyword(s):  
Upper Mantle ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Crust And Upper Mantle ◽  
Seismic Velocity Structure ◽  
Northern Japan

scholarly journals Origins of topography in the western U.S.: Mapping crustal and upper mantle density variations using a uniform seismic velocity model

2014 ◽  
Vol 119 (3) ◽  
pp. 2375-2396 ◽  
Author(s):  
Will Levandowski ◽  
Craig H. Jones ◽  
Weisen Shen ◽  
Michael H. Ritzwoller ◽  
Vera Schulte‐Pelkum
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Velocity Model

Density and composition of the lower mantle

1989 ◽  
Vol 328 (1599) ◽  
pp. 377-389 ◽  
Keyword(s):  
High Pressure ◽  
Density Distribution ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Mineral Assemblage ◽  
Geophysical Data ◽  
Density Difference ◽  
Depth Range ◽  
Density Measurements ◽  
Mantle Composition

The observed density distribution of the lower mantle is compared with density measurements of the (M g,Fe)SiO 3 perovskite and (Mg,Fe)O magnesiowtistite highpressure phases as functions of pressure, tem perature and composition. We find that for plausible bounds on the composition of the upper mantle (ratio of magnesium to iron + magnesium components x M g ^ 0.88) and the temperature in the lower mantle ( T ^ 2000 K), the high-pressure mineral assemblage of upper-mantle composition is at least 2 .6 ( ± 1 ) % less dense than the lower m antle over the depth range 1000-2000 km. Thus, we find that a model of uniform m antle composition is incompatible with the existing mineralogical and geophysical data. Instead, we expect that the mantle is stratified, with the upper and lower m antle convecting separately, and we estimate that the compositional density difference between these regions is about 5 ( + 2) %. The stratification may not be perfect (‘leaky layering’), but significant intermixing and homogenization of the upper and lower m antle over geological timescales are precluded.

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