Structure of S-Wave Velocity in the Crust-Upper Mantle and Tectonic Setting of Strong Earthquakes Beneath Yunnan

2011 ◽  
Vol 54 (3) ◽  
pp. 286-298 ◽  
Author(s):  
Xiao-Man ZHANG ◽  
Jia-Fu HU ◽  
Yi-Li HU ◽  
Hai-Yan YANG ◽  
Jia CHEN ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Tectonic Setting ◽  
S Wave ◽  
Strong Earthquakes

Constraints on the composition of the crust and uppermost mantle in northwestern Canada: Vp/Vs variations along Lithoprobe's SNorCLE transect

2005 ◽  
Vol 42 (6) ◽  
pp. 1205-1222 ◽  
Author(s):  
Gabriela Fernández-Viejo ◽  
Ron M Clowes ◽  
J Kim Welford
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Laboratory Data ◽  
High Ratio ◽  
P Wave ◽  
S Wave ◽  
Uppermost Mantle ◽  
Crust And Upper Mantle ◽  
Slave Craton ◽  
Crustal Composition

Shear-wave seismic data recorded along four profiles during the SNoRE 97 (1997 Slave – Northern Cordillera Refraction Experiment) refraction – wide-angle reflection experiment in northwestern Canada are analyzed to provide S-wave velocity (Vs) models. These are combined with previous P-wave velocity (Vp) models to produce cross sections of the ratio Vp/Vs for the crust and upper mantle. The Vp/Vs values are related to rock types through comparisons with published laboratory data. The Slave craton has low Vp/Vs values of 1.68–1.72, indicating a predominantly silicic crustal composition. Higher values (1.78) for the Great Bear and eastern Hottah domains of the Wopmay orogen imply a more mafic than average crustal composition. In the western Hottah and Fort Simpson arc, values of Vp/Vs drop to ∼1.69. These low values continue westward for 700 km into the Foreland and Omineca belts of the Cordillera, providing support for the interpretation from coincident seismic reflection studies that much of the crust from east of the Cordilleran deformation front to the Stikinia terrane of the Intermontane Belt consists of quartzose metasedimentary rocks. Stikinia shows values of 1.78–1.73, consistent with its derivation as a volcanic arc terrane. Upper mantle velocity and ratio values beneath the Slave craton indicate an ultramafic peridotitic composition. In the Wopmay orogen, the presence of low Vp/Vs ratios beneath the Hottah – Fort Simpson transition indicates the presence of pyroxenite in the upper mantle. Across the northern Cordillera, low Vp values and a moderate-to-high ratio in the uppermost mantle are consistent with the region's high heat flow and the possible presence of partial melt.

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.

scholarly journals Upper Mantle P and S Wave Velocity Structure of the Kalahari Craton and Surrounding Proterozoic Terranes, Southern Africa

2019 ◽  
Vol 46 (16) ◽  
pp. 9509-9518 ◽  
Author(s):  
Kameron Ortiz ◽  
Andrew Nyblade ◽  
Mark Meijde ◽  
Hanneke Paulssen ◽  
Motsamai Kwadiba ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Southern Africa ◽  
Upper Mantle ◽  
Velocity Structure ◽  
S Wave ◽  
Kalahari Craton

Preliminary models of upper mantle P and S wave velocity structure in the western South America region

1999 ◽  
Vol 27 (4-5) ◽  
pp. 567-583 ◽  
Author(s):  
K.L. Kaila ◽  
V.G. Krishna ◽  
G. Khandekar
Keyword(s):  
South America ◽  
Wave Velocity ◽  
Upper Mantle ◽  
Velocity Structure ◽  
S Wave

scholarly journals S-wave velocity structure, mantle xenoliths and the upper mantle beneath the Kaapvaal craton

2006 ◽  
Vol 167 (1) ◽  
pp. 171-186 ◽  
Author(s):  
Angela Marie Larson ◽  
J. Arthur Snoke ◽  
David E. James
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Velocity Structure ◽  
Mantle Xenoliths ◽  
Kaapvaal Craton ◽  
S Wave

Upper mantle shear-wave velocity structure in the Japan region

1974 ◽  
Vol 64 (2) ◽  
pp. 355-374
Author(s):  
K. L. Kaila ◽  
V. G. Krishna ◽  
Hari Narain
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Upper Mantle ◽  
Inflection Point ◽  
Velocity Structure ◽  
Epicentral Distance ◽  
S Wave ◽  
Transition Depth ◽  
Shear Wave Velocity Structure

abstract The upper mantle shear-wave velocity structure in the Japan region has been determined from S travel times of 101 earthquakes with focal depths varying from 40 to 600 km, using a new analytical method given by Kaila (1969). In southwestern Japan, the S velocity obtained as 4.35 km/sec at a 40-km depth remains almost constant to a depth of about 170 km. The shear velocity in northeastern Japan increases linearly from 4.42 km/sec at a depth of 45 km to 4.62 km/sec at a depth of 145-km. For central Japan, the S velocity determined as 4.41 km/sec at a 40-km depth increases linearly to 4.55 km/sec at a 170-km depth, followed by a slight decrease in the velocity gradient, with velocity still increasing linearly to 4.68 km/sec at a depth of 345 km. At this transition depth, there is a first-order velocity discontinuity, the velocity increasing from 4.68 to 4.92 km/sec. Below this depth, velocity again increases linearly from 4.92 to 5.04 km/sec at a depth of 600 km. The shear velocities at depths between 440 to 640 km in Japan are found to be extremely low in comparison to those of Jeffreys (1939), Gutenberg (1959), and Arnold (1967). These low S velocities can explain satisfactorily the late S arrivals from shallow earthquakes between Δ = 20° to 30° as observed in the Japanese region. Graphs have been drawn to show the variation with depth of Δ*, the epicentral distance to the inflection point, Δ1, Δ2, (Δ2 − Δ1), ptrue =∂T/∂Δ, and αS = (T − pΔ) at the inflection point as obtained from the S-wave travel-time analysis.

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