The Deformation Features of Crustal Structure Beneath the East Tibetan Margin and Neighboring Areas

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.501-504.1520 ◽

2014 ◽

Vol 501-504 ◽

pp. 1520-1523

Author(s):

Chang Qing Sun

Keyword(s):

Crustal Structure ◽

Sichuan Basin ◽

Amplitude Ratio ◽

Broad Band ◽

Time Difference ◽

Maximal Energy ◽

Wave Splitting ◽

Deformation Features ◽

Longmenshan Fault ◽

Fault Belt

Shear wave splitting analysis is one of the most commonly used techniques in structural seismology. In this study, the splitting parameters of Moho converted P-to-S phase (Pms), the time difference between maximal energy of qS1 and qS2 and their amplitude ratio were obtained. The data were from 29 broad-band stations across the Longmenshan fault belt. Subsequently, the deformation features of the crustal structure beneath the east Tibetan margin and Sichuan basin were analyzed. Our results show that the time delay and the time difference between maximal energy of qS1 and qS2 in east Tibetan margin is obviously larger than Sichuan basin. However, the amplitude ratio between qS1 and qS2 beneath Longmenshan fault is much smaller than other tectonic sub-regions. These results may suggest the existence of fluid beneath the Longmenshan fault.

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A New Body‐wave Amplitude Ratio‐based Method for Imaging Shallow Crustal Structure and Its Application in the Sichuan Basin, Southwestern China

Geophysical Research Letters ◽

10.1029/2021gl095186 ◽

2021 ◽

Author(s):

Xu Wang ◽

Ling Chen ◽

Huajian Yao

Keyword(s):

Crustal Structure ◽

Sichuan Basin ◽

Wave Amplitude ◽

Amplitude Ratio ◽

Body Wave ◽

Southwestern China ◽

The Sichuan Basin

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Crustal structure across Longmenshan fault belt from passive source seismic profiling

Geophysical Research Letters ◽

10.1029/2009gl039580 ◽

2009 ◽

Vol 36 (17) ◽

Cited By ~ 128

Author(s):

Zhongjie Zhang ◽

Yanghua Wang ◽

Yun Chen ◽

Gregory A. Houseman ◽

Xiaobo Tian ◽

...

Keyword(s):

Crustal Structure ◽

Seismic Profiling ◽

Longmenshan Fault ◽

Fault Belt

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Twin enigmatic microseismic sources in the Gulf of Guinea observed on intercontinental seismic stations

Geophysical Journal International ◽

10.1093/gji/ggt076 ◽

2013 ◽

Vol 194 (1) ◽

pp. 362-366 ◽

Cited By ~ 15

Author(s):

Yingjie Xia ◽

Sidao Ni ◽

Xiangfang Zeng

Keyword(s):

North America ◽

Temporal Variation ◽

Crustal Structure ◽

Source Region ◽

Broad Band ◽

Active Volcano ◽

Gulf Of Guinea ◽

Waveform Data ◽

Seismic Stations ◽

The Earth

Abstract Based on studies of continuous waveform data recorded on broad-band seismograph stations in Africa, Europe and North America, we report evidences for two temporally persistent and spatially localized monochromatic vibrating sources (around 0.036 and 0.038 Hz, respectively) in the Gulf of Guinea, instead of just one source (0.038 Hz or 26 s) found 50 yr ago. The location of the 0.036 Hz source is close to the Sao Tome Volcano, therefore it may be related to volcano processes. However, the 0.038 Hz source cannot be explained with known mechanisms, such as tectonic or oceanic processes. The most likely mechanism is volcano processes, but there is no reported active volcano in source region. Such repetitive vibration sources may provide valuable tools for detecting temporal variation of crustal structure of the Earth.

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Evaluation of crustal inhomogeneity parameters in the southern Longmenshan fault zone and adjacent regions

Journal of Seismology ◽

10.1007/s10950-020-09949-w ◽

2020 ◽

Vol 24 (6) ◽

pp. 1175-1188

Author(s):

Xiao-Ping Fan ◽

Yi-Cheng He ◽

Cong-Jie Yang ◽

Jun-Fei Wang

Keyword(s):

Fault Zone ◽

Lower Crust ◽

Tectonic Deformation ◽

Upper Crust ◽

Crust And Upper Mantle ◽

Study Region ◽

Waveform Data ◽

Longmenshan Fault Zone ◽

Deformation Features ◽

Longmenshan Fault

AbstractBroadband teleseismic waveform data from 13 earthquakes recorded by 70 digital seismic stations were selected to evaluate the inhomogeneity parameters of the crustal medium in the southern Longmenshan fault zone and its adjacent regions using the teleseismic fluctuation wavefield method. Results show that a strong inhomogeneity exists beneath the study region, which can be divided into three blocks according to its structure and tectonic deformation features. These are known as the Sichuan-Qinghai Block, the Sichuan-Yunnan Block, and the Mid-Sichuan Block. The velocity fluctuation ratios of the three blocks are approximately 5.1%, 3.6%, and 5.1% in the upper crust and 5.1%, 3.8%, and 4.9% in the lower crust. The inhomogeneity correlation lengths of the three blocks are about 10.1 km, 14.0 km, and 10.7 km in the upper crust and 11.8 km, 17.0 km, and 11.8 km in the lower crust. The differences in the crustal medium inhomogeneity beneath the Sichuan-Yunnan Block, the Sichuan-Qinghai Block, and the Mid-Sichuan Block may be related to intensive tectonic movement and material flow in the crust and upper mantle.

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The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting

Geophysics ◽

10.1190/1.3205028 ◽

2009 ◽

Vol 74 (5) ◽

pp. B183-B195 ◽

Cited By ~ 40

Author(s):

K. De Meersman ◽

J.-M. Kendall ◽

M. van der Baan

Keyword(s):

Seismic Anisotropy ◽

Amplitude Ratio ◽

Temporal Variations ◽

Oil Field ◽

P Wave ◽

Wave Form ◽

S Wave ◽

Data Set ◽

Wave Splitting ◽

Source Mechanisms

We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semiautomated array analysis method repicks the P- and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a [Formula: see text]-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest–south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.

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Key seismic survey technologies for deep complex geological structures: A case study of the northern section of the Longmenshan Fault Fold Belt in the Sichuan Basin

Natural Gas Industry B ◽

10.1016/j.ngib.2018.01.010 ◽

2018 ◽

Vol 5 (4) ◽

pp. 360-370 ◽

Cited By ~ 1

Author(s):

Luzi Zhao ◽

Guangrong Zhang ◽

Wei Chen ◽

Yong Peng ◽

Bing Xie ◽

...

Keyword(s):

Sichuan Basin ◽

Seismic Survey ◽

Fold Belt ◽

Geological Structures ◽

Longmenshan Fault ◽

The Sichuan Basin

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Sharpness of the 410-km discontinuity from the P410s and P2p410s seismic phases

Geophysical Journal International ◽

10.1093/gji/ggz507 ◽

2019 ◽

Cited By ~ 1

Author(s):

Lev Vinnik ◽

Yangfan Deng ◽

Grigoriy Kosarev ◽

Sergey Oreshin ◽

Zhou Zhang ◽

...

Keyword(s):

Transition Zone ◽

Southern Africa ◽

Amplitude Ratio ◽

Southern China ◽

Broad Band ◽

Receiver Functions ◽

P Wave ◽

Seismic Model ◽

Yangtze Craton ◽

Zone Water

Summary Sharpness of the 410-km boundary is of interest because it is sensitive to water content in the transition zone. We evaluate the width of the 410-km discontinuity with a new seismic method. Our estimates are inferred from the amplitude ratio of the P2p410s and P410s seismic phases that are detected in P-wave receiver functions. We applied this method to seismic recordings from arrays of broad-band stations deployed in central Fennoscandia, southern Africa and southern China. The obtained estimates of width of the 410-km discontinuity range from 10 to 22 km and always exceed the width of 7 km which is expected for anhydrous conditions. The enlarged width may be interpreted in terms of hydrous conditions, but we have found only one region (the eastern Yangtze Craton in China) where the broad 410-km discontinuity, as expected, is accompanied by a broad transition zone. Water in the transition zone may be a kind of a global phenomenon, but evidence of the enlarged width of the transition zone may be missing in most of our data because the reference seismic model is affected by water, as well.

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Shear wave splitting as diagnostics of variable tectonic fabrics across the Eastern Alps – Bohemian Massif contact zone

10.5194/egusphere-egu2020-7757 ◽

2020 ◽

Author(s):

Luděk Vecsey ◽

Jaroslava Plomerová ◽

Vladislav Babuška ◽

the AlpArray-EASI Working Group ◽

the AlpArray Working Group

Keyword(s):

Shear Wave ◽

Bohemian Massif ◽

Upper Mantle ◽

Large Scale ◽

Broad Band ◽

Eastern Alps ◽

Shear Wave Splitting ◽

Splitting Methods ◽

Mantle Lithosphere ◽

Wave Splitting

We examine lateral variations of shear-wave splitting evaluated from data recorded during the passive seismic experiments AlpArray-EASI (2014-2015) and AlpArray Seismic Network (2016-2019). The swath about 200 km broad and 540 km long along 13.3&#176; E longitude was selected to study the large-scale anisotropy in the mantle lithosphere beneath the Bohemian Massif (BM) and the Eastern Alps. The region is covered by about 200 broad-band temporary and permanent stations.The shear-wave splitting evaluation consists of several steps: it starts by automated identification and pre-processing of SKS waveforms, filtering and quality check. Then we analyse and, if needed, also correct seismic waveforms for seismometer mis-orientations of all stations used. To improve results of splitting analysis of signals distorted by noise, we carefully apply two splitting methods (eigenvalue, transverse energy). We stack splitting measurements for waves closely propagating within the upper mantle and include particle motion analysis. The modified version of the splitting methods (Vecsey et al., 2008) enables us to retrieve 3-D orientation of large-scale anisotropic structures in the mantle lithosphere and deformations within the sub-lithospheric part of the upper mantle.Both the evaluated shear-wave splitting parameters and the particle motions are consistent within sub-regions of the Alpine and BM upper mantle and exhibit significant and often sudden lateral changes across the whole region. We relate such changes to sharply bounded anisotropic domains with uniform fossil fabrics in the mantle lithosphere.

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