scholarly journals Crustal and mantle velocity models of southern Tibet from finite frequency tomography

2011 ◽  
Vol 116 (B2) ◽  
Author(s):  
Xiaofeng Liang ◽  
Yang Shen ◽  
Yongshun John Chen ◽  
Yong Ren
Keyword(s):  
Finite Frequency ◽  
Southern Tibet ◽  
Velocity Models ◽  
Mantle Velocity

scholarly journals Mantle earthquakes in the Himalayan collision zone

Geology ◽  
2019 ◽  
Vol 47 (9) ◽  
pp. 815-819 ◽  
Author(s):  
Vera Schulte-Pelkum ◽  
Gaspar Monsalve ◽  
Anne F. Sheehan ◽  
Peter Shearer ◽  
Francis Wu ◽  
...  
Keyword(s):  
Receiver Functions ◽  
Ductile Material ◽  
Current Debate ◽  
Southern Tibet ◽  
Crustal Layer ◽  
Cold Temperatures ◽  
Velocity Models ◽  
Delay Times ◽  
Deep Seismicity ◽  
And Migration

Abstract Earthquakes are known to occur beneath southern Tibet at depths up to ∼95 km. Whether these earthquakes occur within the lower crust thickened in the Himalayan collision or in the mantle is a matter of current debate. Here we compare vertical travel paths expressed as delay times between S and P arrivals for local events to delay times of P-to-S conversions from the Moho in receiver functions. The method removes most of the uncertainty introduced in standard analysis from using velocity models for depth location and migration. We show that deep seismicity in southern Tibet is unequivocally located beneath the Moho in the mantle. Deep seismicity in continental lithosphere occurs under normally ductile conditions and has therefore garnered interest in whether its occurrence is due to particularly cold temperatures or whether other factors are causing embrittlement of ductile material. Eclogitization in the subducting Indian crust has been proposed as a cause for the deep seismicity in this area. Our observation of seismicity in the mantle, falling below rather than within the crustal layer with proposed eclogitization, requires revisiting this concept and favors other embrittlement mechanisms that operate within mantle material.

scholarly journals Imaging with pre-stack migration based on Sp scattering kernels

2019 ◽  
Vol 220 (1) ◽  
pp. 428-449 ◽  
Author(s):  
Junlin Hua ◽  
Karen M Fischer ◽  
Nicholas J Mancinelli ◽  
Tiezhao Bao
Keyword(s):  
Scattering Amplitude ◽  
Receiver Functions ◽  
Fast Marching Method ◽  
Fast Marching ◽  
Velocity Models ◽  
Conversion Point ◽  
Mantle Discontinuities ◽  
Migration Method ◽  
Mantle Velocity ◽  
Positive Interference

SUMMARY Sp receiver functions have been widely used to detect the lithosphere–asthenosphere boundary (LAB) and other mantle discontinuities. However, traditional common conversion point (CCP) stacking can be biased by the assumption of horizontal layers and this method typically underestimates scattering amplitudes from velocity boundaries with significant dips. A new pre-stack migration method based on recently developed Sp scattering kernels offers an alternative that more accurately captures the timing and amplitude of scattering. When calculating kernels, Sp-S times are estimated with the fast-marching method, and scattering amplitude versus direction, geometrical spreading and phase shifts are accounted for. To minimize imaging artefacts with larger station spacing, Sp receiver functions are interpolated to more closely spaced pseudo-stations using either compressive sampling or spatial averaging algorithms. To test the kernel-based stacking method, synthetic Sp phases were predicted using SPECFEM2D for velocity models with a flat Moho and a negative mantle velocity gradient with a ramp structure. The kernel-based stacking method resolves horizontal interfaces equally well as CCP stacking and outperforms CCP stacking when imaging boundaries with dips of more than 8°, although dip resolution is still limited. Use of more vertically incident phases such as SKSp improves retrieval of dipping discontinuity segments. A second approach is to down-weight the portions of the kernels that have the greatest positive interference among neighbouring stations, thus enhancing scattering from dipping structures where positive interference is lower. With this downweighting, the kernel-based stacking method applied to Sp data is able to continuously resolve LAB discontinuities with dips up to 15° and to partially resolve continuous LAB discontinuities with dips of ∼20°. The intrinsic properties of teleseismic Sp phase kernels limit their ability to resolve LAB structures with dips of ∼20–35°, but still larger dips of ∼40–50° are resolvable with dense and appropriately placed stations. Analysis of Sp scattering kernels also explains the effectiveness of CCP stacking for quasi-horizontal interfaces.

Author response for "Neo-Tethyan slab tearing constrained by Palaeocene N-MORB-like magmatism in southern Tibet"

2020 ◽  
Author(s):  
Ye Tian ◽  
Feng Huang ◽  
Jifeng Xu ◽  
Baodi Wang ◽  
Han Liu ◽  
...  
Keyword(s):  
Author Response ◽  
Southern Tibet ◽  
Slab Tearing
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