Penetration of mid-crustal low velocity zone across the Kunlun Fault in the NE Tibetan Plateau revealed by ambient noise tomography

2014 ◽  
Vol 406 ◽  
pp. 81-92 ◽  
Author(s):  
Chengxin Jiang ◽  
Yingjie Yang ◽  
Yong Zheng
Keyword(s):  
Tibetan Plateau ◽  
Ambient Noise ◽  
Ambient Noise Tomography ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Velocity Zone ◽  
Ne Tibetan Plateau

scholarly journals Imaging Karatungk Cu-Ni Mine in Xinjiang, Western China with a Passive Seismic Array

Minerals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 601 ◽  
Author(s):  
Peixiao Du ◽  
Jing Wu ◽  
Yang Li ◽  
Jian Wang ◽  
Chunming Han ◽  
...  
Keyword(s):  
High Velocity ◽  
Ambient Noise ◽  
Joint Inversion ◽  
Wave Structure ◽  
Seismic Array ◽  
Western China ◽  
Ambient Noise Tomography ◽  
Magma Intrusion ◽  
Low Velocity ◽  
Velocity Zone

Karatungk Mine is the second-largest Cu-Ni sulfide mine in China. However, the detailed structure beneath the mine remains unclear. Using continuous waveforms recorded by a dense temporary seismic array, here we apply ambient noise tomography to study the shallow crustal structure of Karatungk Mine down to ~1.3 km depth. We obtain surface-wave dispersions at 0.1–1.5 s by calculating cross-correlation functions, which are inverted for 3D shear-wave structure at the top-most (0–1.3 km) crust by a joint inversion of group and phase dispersions. Our results show that low-velocity zones beneath Y1 ore-hosting intrusion (hereafter called Y1) at 0–0.5 km depth and northwest of the Y2 ore-hosting intrusion (hereafter called Y2) at 0–0.6 km depth are consistent with highly mineralized areas. A relatively high-velocity zone is connected with a weakly mineralized area located to the southeast of Y2 and Y3 (hereafter called Y3) ore-hosting intrusions. Two high-velocity zones, distributed at 0.7–1.3 km depth in the northernmost and southernmost parts of the study area respectively, are interpreted to be igneous rocks related to early magma intrusion. Furthermore, the low-velocity zone at 0.7–1.3 km depth in the middle of the study area may be related to: a possible channel related to initial magma transport; mine strata or a potentially mineralized area. This study demonstrates a new application of dense-array ambient noise tomography to a mining area that may guide future studies of mineralized regions.

Partial melting and the low-velocity zone

1970 ◽  
Vol 4 (1) ◽  
pp. 62-64 ◽  
Author(s):  
Don L. Anderson ◽  
Hartmut Spetzler
Keyword(s):  
Partial Melting ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Velocity Zone

Nature of the low velocity zone in Cascadia from receiver function waveform inversion

2012 ◽  
Vol 337-338 ◽  
pp. 25-38 ◽  
Author(s):  
Ralf T.J. Hansen ◽  
Michael G. Bostock ◽  
Nikolas I. Christensen
Keyword(s):  
Receiver Function ◽  
Waveform Inversion ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Velocity Zone

scholarly journals Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

2021 ◽  
Author(s):  
JD Eccles ◽  
AK Gulley ◽  
PE Malin ◽  
CM Boese ◽  
John Townend ◽  
...  
Keyword(s):  
Fault Zone ◽  
Plate Boundary ◽  
Guided Wave ◽  
S Wave ◽  
Low Velocity ◽  
Catchment Scale ◽  
Near Surface ◽  
Low Velocity Zone ◽  
Alpine Fault ◽  
Velocity Zone

© 2015. American Geophysical Union. All Rights Reserved. Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35Hz) have been recorded on shallow borehole seismometers installed within 20m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

Topology of ray surfaces in low-velocity zones

1979 ◽  
Vol 69 (2) ◽  
pp. 369-378
Author(s):  
George A. McMechan
Keyword(s):  
Guided Waves ◽  
Turning Points ◽  
Three Dimensional ◽  
Focal Depth ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Ray Trajectories ◽  
Definition Of ◽  
Single Set ◽  
Velocity Zone

abstract Plotting of three-dimensional ray surfaces in p-Δ-z space provides a means of determining p-Δ curves for any focal depth. A region of increasing velocity with depth is represented in p-Δ-z space by a trough, and a region of decreasing velocity, by a crest. Two sets of ray trajectories, the arrivals refracted outside a low-velocity zone, and the guided waves inside the zone, can be merged into a single set along the ray that splits into two at the top of the low-velocity zone. This ray is common to both sets. This construction provides continuity of the locus of ray turning points through the low-velocity zone and thus allows definition of p-Δ curves inside as well as outside the low-velocity zone.

First step towards an integrated geophysical-geological model of the W-Alps: A new Vs model from transdimensional ambient-noise tomography

2021 ◽  
Author(s):  
Ahmed Nouibat ◽  
Laurent Stehly ◽  
Anne Paul ◽  
Romain Brossier ◽  
Thomas Bodin ◽  
...  
Keyword(s):  
Group Velocity ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Receiver Functions ◽  
Time Inversion ◽  
Geological Model ◽  
Ambient Noise Tomography ◽  
Low Velocity

<p><span>We have successfully derived a new </span><span>3-D</span><span> high resolution shear wave velocity model of the crust and uppermost mantle of a large part of W-Europe from transdimensional</span><span><strong> </strong></span><span>ambient-noise tomography. This model is intended to contribute to the development of the first </span><span>3-D</span><span> crustal-scale integrated geophysical-geological model of the W-Alps to deepen understanding of orogenesis and its relationship to mantle dynamics. </span></p><p><span>We used an exceptional dataset of 4 years of vertical-component, daily seismic noise records (2015 - 2019) of more than 950 permanent broadband seismic stations located in and around the Greater Alpine region, complemented by 490 temporary stations from the AlpArray sea-land seismic network and 110 stations from Cifalps dense deployments.</span></p><p><span>We firstly performed a </span><span>2-D</span><span> data-driven transdimensional travel time inversion for group velocity maps from 4 to 150 s (Bodin & Sambridge, 2009). The data noise level was treated as a parameter of the inversion problem, and determined within a Hierarchical Bayes method. We used Fast Marching Eikonal solver (Rawlinson & Sambridge, 2005) jointly with the reversible jump algorithm to update raypath geometry during inversion. In the inversion of group velocity maps for shear-wave velocity, we set up a new formulation of the</span><span> approach proposed by Lu et al (2018) by including group velocity uncertainties. Posterior probability distributions on </span><span>Vs</span><span> and interfaces were estimated by exploring a set of 130 millions synthetic </span><span>4-</span><span>layer </span><span>1-D Vs</span><span> models that allow for </span><span>low-velocity zones</span><span><em>.</em></span><span> The obtained probabilistic model was refined using a linearized inversion</span><span><em>. </em></span><span>For the ocean-bottom seismometers of the Ligurian-Provencal basin, we applied a specific processing to clean daily noise signals from instrumental and oceanic noises (Crawford </span><span>&</span><span> Webb, 2000) and adapted the inversion for Vs to include the water column.</span></p><p>Our Vs model evidences strong variations of the crustal structure along strike, particulary in the subduction complex. The European crust includes lower crustal low-velocity zones and a Moho jump of ~8-12 km beneath the W-boundary of the external crystalline massifs. We observe a deep LVZ<em> </em>structure (50 - 80 km) in the prolongation<em> </em>of the European continental subduction beneath the Ivrea body. The striking fit between the receiver functions ccp migrated section across the Cifalps profile and this new Vs model validate its reliability.</p>

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