scholarly journals Magnitude and symmetry of seismic anisotropy in mica‐ and amphibole‐bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast Tibetan Plateau

2015 ◽  
Vol 120 (9) ◽  
pp. 6404-6430 ◽  
Author(s):  
Shaocheng Ji ◽  
Tongbin Shao ◽  
Katsuyoshi Michibayashi ◽  
Shoma Oya ◽  
Takako Satsukawa ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Seismic Data ◽  
Seismic Anisotropy ◽  
Metamorphic Rocks ◽  
Tectonic Interpretation ◽  
Southeast Tibetan Plateau

Integrated VTI model building with seismic data, geologic information, and rock-physics modeling — Part 1: Theory and synthetic test

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. C177-C191 ◽  
Author(s):  
Yunyue Li ◽  
Biondo Biondi ◽  
Robert Clapp ◽  
Dave Nichols
Keyword(s):  
Seismic Data ◽  
Seismic Anisotropy ◽  
Model Building ◽  
Rock Physics ◽  
Seismic Inversion ◽  
Additional Information ◽  
Synthetic Test ◽  
Rock Physics Modeling ◽  
Physics Modeling ◽  
Geologic Information

Seismic anisotropy plays an important role in structural imaging and lithologic interpretation. However, anisotropic model building is a challenging underdetermined inverse problem. It is well-understood that single component pressure wave seismic data recorded on the upper surface are insufficient to resolve a unique solution for velocity and anisotropy parameters. To overcome the limitations of seismic data, we have developed an integrated model building scheme based on Bayesian inference to consider seismic data, geologic information, and rock-physics knowledge simultaneously. We have performed the prestack seismic inversion using wave-equation migration velocity analysis (WEMVA) for vertical transverse isotropic (VTI) models. This image-space method enabled automatic geologic interpretation. We have integrated the geologic information as spatial model correlations, applied on each parameter individually. We integrate the rock-physics information as lithologic model correlations, bringing additional information, so that the parameters weakly constrained by seismic are updated as well as the strongly constrained parameters. The constraints provided by the additional information help the inversion converge faster, mitigate the ambiguities among the parameters, and yield VTI models that were consistent with the underlying geologic and lithologic assumptions. We have developed the theoretical framework for the proposed integrated WEMVA for VTI models and determined the added information contained in the regularization terms, especially the rock-physics constraints.

scholarly journals Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden

2020 ◽  
Author(s):  
Felix Kästner ◽  
Simona Pierdominici ◽  
Judith Elger ◽  
Christian Berndt ◽  
Alba Zappone ◽  
...  
Keyword(s):  
Seismic Anisotropy ◽  
Seismic Velocity ◽  
Metamorphic Rocks ◽  
Seismic Velocities ◽  
Mafic Rocks ◽  
Seismic Properties ◽  
The Core ◽  
Nappe Complex ◽  
Thrust Zone ◽  
Mountain Belts

<p>Deeply rooted thrust zones are key features of tectonic processes and the evolution of mountain belts. Exhumed and deeply-eroded orogens like the Scandinavian Caledonides allow to study such systems from the surface. Previous seismic investigations of the Seve Nappe Complex have shown indications for a strong but discontinuous reflectivity of this thrust zone, which is only poorly understood. The correlation of seismic properties measured on borehole cores with surface seismic data can help to constrain the origin of this reflectivity. In this study, we compare seismic velocities measured on cores to in situ velocities measured in the borehole. The core and downhole velocities deviate by up to 2 km/s. However, velocities of mafic rocks are generally in close agreement. Seismic anisotropy increases from about 5 to 26 % at depth, indicating a transition from gneissic to schistose foliation. Differences in the core and downhole velocities are most likely the result of microcracks due to depressurization of the cores. Thus, seismic velocity can help to identify mafic rocks on different scales whereas the velocity signature of other lithologies is obscured in core-derived velocities. Metamorphic foliation on the other hand has a clear expression in seismic anisotropy. To further constrain the effects of mineral composition, microstructure and deformation on the measured seismic anisotropy, we conducted additional microscopic investigations on selected core samples. These analyses using electron-based microscopy and X-ray powder diffractometry indicate that the anisotropy is strongest for mica schists followed by amphibole-rich units. This also emphasizes that seismic velocity and anisotropy are of complementary importance to better distinguish the present lithological units. Our results will aid in the evaluation of core-derived seismic properties of high-grade metamorphic rocks at the COSC-1 borehole and elsewhere.</p>

Gas geochemistry of the hot spring in the Litang fault zone, Southeast Tibetan Plateau

2017 ◽  
Vol 79 ◽  
pp. 17-26 ◽  
Author(s):  
Xiaocheng Zhou ◽  
Lei Liu ◽  
Zhi Chen ◽  
Yueju Cui ◽  
Jianguo Du
Keyword(s):  
Tibetan Plateau ◽  
Fault Zone ◽  
Hot Spring ◽  
Gas Geochemistry ◽  
Southeast Tibetan Plateau

Seismic anisotropy

Geophysics ◽  
2001 ◽  
Vol 66 (1) ◽  
pp. 40-41 ◽  
Author(s):  
Leon Thomsen
Keyword(s):  
Future Development ◽  
Seismic Data ◽  
Seismic Anisotropy ◽  
Practical Interest ◽  
Exploration And Exploitation ◽  
Principal Reason ◽  
The Past ◽  
High Level ◽  
Effective Use

The topic of seismic anisotropy in exploration and exploitation has seen a great deal of progress in the past decade‐and‐a‐half. The principal reason for this is the increased (and increasing) quality of seismic data, of the processing done to it, and of the interpretation expected from it. No longer an academic subject of little practical interest, it is now often viewed as one of the crucial factors which, if not taken into account, severely hampers our effective use of the data. The following brief overview is not intended to be exhaustive, since any such attempt would surely be incomplete. However, it does provide a high‐level survey of the advances seen (at the end of this period) to be important by one who was closely involved, and it directly extrapolates this history to predict the future development of the topic.

Crustal anisotropy beneath northeastern Tibetan Plateau from the harmonic decomposition of receiver functions

2019 ◽  
Vol 220 (3) ◽  
pp. 1585-1603
Author(s):  
Zhenxin Xie ◽  
Vadim Levin ◽  
Qingju Wu
Keyword(s):  
Tibetan Plateau ◽  
Seismic Anisotropy ◽  
Receiver Function ◽  
Flow Direction ◽  
Receiver Functions ◽  
Low Velocity ◽  
Northeastern Tibetan Plateau ◽  
Harmonic Decomposition ◽  
Anisotropic Layers ◽  
Qilian Orogen

SUMMARY A uniformly spaced linear transect through the northeastern Tibetan Plateau was constructed using 54 stations from ChinaArray Phase II. We used a set of colocated earthquakes to form receiver function beams that were then used to construct a 2-D image of main converting boundaries in our region and to investigate lateral changes in main impedance contrasts along the transect. The image revealed obvious mid-crustal low-velocity zones beneath the Qilian Orogen and the Alxa Block. We developed a new procedure that uses harmonically decomposed receiver functions to characterize seismic anisotropy, and that can determine both the orientations of symmetry axes and their type (fast or slow). We tested our technique on a number of synthetic models, and subsequently applied it to the data from the transect. We found that: (1) within the upper crust the orientations of slow symmetry axes are nearly orthogonal to the strike directions of faults, and thus anisotropy is likely caused by the shape preferred orientation of fluid-saturated cracks or fractures and (2) together with the low-velocity zones revealed from receiver functions stacks, anisotropic layers in the middle-to-lower crust could be explained by the crustal channel flow that was proposed for this region by previous studies. The shear within the boundary layers of crustal flow forms anisotropy with symmetry axes parallel to the flow direction.

scholarly journals Constraining the Water Cycle Model of an Important Karstic Catchment in Southeast Tibetan Plateau Using Isotopic Tracers (2H, 18O, 3H, 222Rn)

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3306
Author(s):  
Dawei Liao ◽  
Zhonghe Pang ◽  
Weiyang Xiao ◽  
Yinlei Hao ◽  
Jie Du ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Water Cycle ◽  
Water Source ◽  
Natural World ◽  
World Heritage Site ◽  
Cycle Model ◽  
Isotopic Tracers ◽  
Geological Conditions ◽  
Local Water ◽  
Southeast Tibetan Plateau

Understanding the connectivity between surface water and groundwater is key to sound geo-hazard prevention and mitigation in a waterscape such as the Jiuzhaigou Natural World Heritage Site in the southeast Tibetan Plateau, China. In this study, we used environmental isotope tracers (2H, 18O 3H, and 222Rn) to constrain a water cycle model including confirming hydrological pathways, connectivity, and water source identification in the Jiuzhaigou catchments. We established the local meteoric water line (LMWL) based on the weekly precipitation isotope sampling of a precipitation station. We systematically collected water samples from various water bodies in the study area to design the local water cycle model. The regional water level and discharge changes at one month after the earthquake indicated that there was a hydraulic connection underground across the local water divide between the Rize (RZ) river in the west and Zechawa (ZCW) lake in the east by the δ18O and δ2H measurements. We employed an end-member mixing model to identify and quantify Jiuzhaigou runoff-generating sources and their contributions, and we found that the average contributions of precipitation and groundwater to the surface runoff in the catchments are about 30% and 70%, respectively. The two branches of the Shuzheng (SZ) trunk were recharged by 62 ± 19% from the ZCW lake and 38 ± 19% from the RZ river, which was consistent with the fractions calculated by the actual discharge volume. 222Rn mass balance analyses were employed to estimate the water exchange between groundwater and river, which further confirmed this estimate. 222Rn concentrations and 3H contents showed that the groundwater had a short residence time and it was moderate precipitation, thought the contribution of groundwater to the river was 70%, according to the different tracers. A three-dimensional conceptual model of the water cycle that integrated the regional hydrological and geological conditions was established for the catchments.

Sign in / Sign up

Export Citation Format

Share Document