Anticorrelated Seismic Velocity Anomalies from Post-Perovskite in the Lowermost Mantle

Science ◽  
2008 ◽  
Vol 320 (5879) ◽  
pp. 1070-1074 ◽  
Author(s):  
A. R. Hutko ◽  
T. Lay ◽  
J. Revenaugh ◽  
E. J. Garnero
Keyword(s):  
Seismic Velocity ◽  
Velocity Anomalies ◽  
Lowermost Mantle

Deep origin of mid-ocean-ridge seismic velocity anomalies

Nature ◽  
1992 ◽  
Vol 360 (6400) ◽  
pp. 149-152 ◽  
Author(s):  
Wei-jia Su ◽  
Robert L. Woodward ◽  
Adam M. Dziewonski
Keyword(s):  
Seismic Velocity ◽  
Mid Ocean Ridge ◽  
Velocity Anomalies ◽  
Ocean Ridge

Lateral inhomogeneities in P velocity under the Tarbela array of the lesser Himalayas of Pakistan

1977 ◽  
Vol 67 (3) ◽  
pp. 725-734
Author(s):  
William H. Menke
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Lower Crust ◽  
Seismic Velocity ◽  
Three Dimensional ◽  
Horizontal Layer ◽  
Main Central Thrust ◽  
Crust And Upper Mantle ◽  
Lesser Himalayas ◽  
Velocity Anomalies

abstract Three-dimensional seismic-velocity heterogeneities (to a depth of 125 km) under the Tarbela array are determined by the Aki et al. (1976a) method of inverting teleseismic travel-time residuals. Velocity anomalies are clearly present and are elongated in the northwest direction. An overall 2 to 3 per cent decrease in velocity to the northeast is observed across any horizontal layer. These features result from a 4° dip of geologic structures in the direction N41°E. This direction is similar to some observed trends of seismicity in the Tarbela area and to the trend of the Himalayan Main Central Thrust (MCT) east and north of Tarbela, but not to the trend of the fault traces nor the strike of geologic structures in the Tarbela area. Just to the southeast of the Tarbela array, these faults bend sharply westward, forming a mountainous loop. In this study it is concluded that the westerly trending fault traces and westerly striking geology are both only surficial and not representative of structures at greater depth. These deep structures within the lower crust and upper mantle preserve a strike similar to more eastern areas along the MCT. They are shown to be volumetrically and tectonically the more important features.

scholarly journals Case Study - Seismic Velocity Anomalies Analysis for Gas Detection in Potiguar Basin

2019 ◽  
Author(s):  
Frank Bulhões ◽  
Gleidson Ferreira ◽  
Rogério Santos ◽  
José Lira ◽  
Julio Carvalho ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Gas Detection ◽  
Potiguar Basin ◽  
Velocity Anomalies

Long-wavelength variations in Earth’s geoid: physical models and dynamical implications

1989 ◽  
Vol 328 (1599) ◽  
pp. 309-327 ◽  
Keyword(s):  
Lower Mantle ◽  
Seismic Velocity ◽  
Major Effect ◽  
Physical Models ◽  
Earth Model ◽  
Dynamic Topography ◽  
Long Wavelength ◽  
Low Viscosity ◽  
Velocity Anomalies

The seismic velocity anomalies resolved by seismic tomography are associated with variations in density that lead to convective flow and to dynamically maintained topography at the Earth’s surface, the core-mantle boundary (CMB), and any interior chemical boundaries that might exist. The dynamic topography resulting from a given density field is very sensitive to viscosity structure and to chemical stratification. The mass anomalies resulting from dynamic topography have a major effect on the geoid, which places strong constraints on mantle structure. Almost 90% of the observed geoid can be explained by density anomalies inferred from tomography and a model of subducted slabs, along with the resulting dynamic topography predicted for an Earth model with a low-viscosity asthenosphere ( ca . 10 20 Pa s) overlying a moderate viscosity ( ca . 10 22.5 Pa s) lower mantle. This viscosity stratification would lead to rapid mixing in the asthenosphere, with little mixing in the lower mantle. Chemically stratified models can also explain the geoid, but they predict hundreds of kilometres of dynamic topography at the 670 km discontinuity, a prediction currently unsupported by observation. A low-viscosity or chemically distinct D" layer tends to decouple CMB topography from convective circulation in the overlying mantle. Dynamic topography at the surface should result in long-term changes in eustatic sea level.

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