Three-Dimensional Velocity Images of the Crust and Upper Mantle beneath the North-South Zone in China

2005 ◽  
Vol 95 (3) ◽  
pp. 916-925 ◽  
Author(s):  
Y. Liu
Keyword(s):  
Upper Mantle ◽  
Three Dimensional ◽  
Crust And Upper Mantle ◽  
The North ◽  
Velocity Images ◽  
South Zone

Three-dimensional velocity images beneath the Kang–Dian Tethyan tectonic zone of China

2002 ◽  
Vol 39 (10) ◽  
pp. 1517-1525 ◽  
Author(s):  
Yike Liu ◽  
Xu Chang ◽  
Futian Liu ◽  
Ye Zheng
Keyword(s):  
Upper Mantle ◽  
Three Dimensional ◽  
P Wave ◽  
Low Velocity ◽  
Tectonic Structures ◽  
Crust And Upper Mantle ◽  
Tectonic Zone ◽  
Imaging Results ◽  
Wide Range ◽  
Velocity Images

Three-dimensional velocity images of the crust and upper mantle beneath the Kang–Dian Tethyan tectonic zone in China are constructed using P-wave travel-time residuals of earthquakes. The Kang–Dian Tethyan tectonic zone is a transitional zone in tectonic structures and an important topographic border line. It is also a zone of concentration of shallow-focus earthquakes. The imaging results indicate that there is a significant lateral heterogeneity in the crust and upper mantle beneath the Kang–Dian Tethyan tectonic zone in China. The velocity images of the upper crust show features closely related to the tectonic features on the surface. A low-velocity layer exists in a very wide range of the mid-crust. Almost all of the major earthquakes took place in the transition strips between high- and low-velocity zones in the crust above 20 km depth. From the velocity images at 20+0 and 50+0 km depth, respectively, we find that the epicenters of strong earthquakes with magnitude larger than 6.0 are almost entirely distributed in the low-velocity zones or on their boundaries.

Electromagnetic images of the Trans-Hudson orogen: the North American Central Plains anomaly revealed

2005 ◽  
Vol 42 (4) ◽  
pp. 457-478 ◽  
Author(s):  
Alan G Jones ◽  
Juanjo Ledo ◽  
Ian J Ferguson
Keyword(s):  
Electrical Properties ◽  
North American ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Three Dimensional ◽  
Conductivity Anomaly ◽  
Central Plains ◽  
Slave Craton ◽  
The North ◽  
Kimberlite Field

Magnetotelluric studies of the Trans-Hudson orogen over the last two decades, prompted by the discovery of a significant conductivity anomaly beneath the North American Central Plains (NACP), from over 300 sites yield an extensive database for interrogation and enable three-dimensional information to be obtained about the geometry of the orogen from southern North Dakota to northern Saskatchewan. The NACP anomaly is remarkable in its continuity along strike, testimony to along-strike similarity of orogenic processes. Where bedrock is exposed, the anomaly can be associated with sulphides that were metamorphosed during subduction and compression and penetratively emplaced deep within the crust of the internides of the orogen to the boundary of the Hearne margin. A new result from this compilation is the discovery of an anomaly within the upper mantle beginning at depths of ~80–100 km. This lithospheric mantle conductor has electrical properties similar to those for the central Slave craton mantle conductor, which lies directly beneath the major diamond-producing Lac de Gras kimberlite field. While the Saskatchewan mantle conductor does not directly underlie the Fort à la Corne kimberlite, which is associated with the Sask craton, the spatial correspondence is close.

Azimuth and slowness anomalies of seismic waves measured on the central California seismographic array. Part I. Observations

1966 ◽  
Vol 56 (1) ◽  
pp. 223-239 ◽  
Author(s):  
Michio Otsuka
Keyword(s):  
Upper Mantle ◽  
Measurement Errors ◽  
Seismic Waves ◽  
Crust And Upper Mantle ◽  
Arrival Times ◽  
Central California ◽  
The North ◽  
Upper Mantle Structure ◽  
Coast Ranges ◽  
The University

abstract Arrays of seismographs are usually considered to be detectors which give enhanced signals from distant earthquakes. They also provide, however, a new way of learning more about the structure of the crust and upper mantle. The deviation of the seismic-wave surface from its expected configuration may be regarded as a consequence of non-homogeneous and anisotropic conditions in the earth. The operations of the University of California network of telemetry stations in the Coast Ranges of California provides an opportunity to discover the practicality of this approach. The situation of this network near the continental margin gives the study particular interest. The differences in arrival-times between array elements of coherent peaks or troughs of P and pP phases from 28 teleseisms in the period of 1963-1964 were read from the telemetry records of the central California seismographic array. The direction of approach and velocities of the wave fronts were then determined and compared with the great circle azimuths and with the apparent velocities calculated from the Jeffreys-Bullen tables. The observed anomalies in direction of approach and apparent velocites are found to be cyclic functions of the direction of the source. The amplitudes of these functions are almost 10 degrees in azimuth anomaly and 1.0 sec/deg in slowness anomaly. Error analyses show that the anomaly functions cannot be attributed to the measurement errors. The derived anomaly functions provide a powerful means of examining crustal and upper mantle structure under the array and perhaps at the source. Variations between subsets of the array indicate significant differences in structure between portions of the Coast Ranges to the north and to the south of Hollister.

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