Stress state of the Baoxing segment of the southwestern Longmenshan Fault Zone before and after the M s 7.0 Lushan earthquake

Abstract. The b-value in the Gutenberg-Richter frequency-magnitude distribution, which is assumed to be related to stress heterogeneity or asperities, was mapped along the Longmenshan fault zone which accommodated the 12 May 2008, Wenchuan, MS 8.0 earthquake. Spatial distributions of b-value before and after the Wenchuan earthquake, respectively, were compared with the slip distribution of the mainshock. It is shown that the mainshock rupture nucleated near to, but not within, the high-stress (low b-value) asperity in the south part of the Longmenshan fault, propagating north-eastward to the relatively low stress (high b-value) region. Due to the significant difference between the rupture process results from different sources, the comparison between slip distribution and pre-seismic b-value distribution leads to only conclusion of the rule-of-thumb. The temporal change of b-value before the mainshock shows a weak trend of decreasing, being hard to be used as an indicator of the approaching of the mainshock. Distribution of b-values for the aftershocks relates the termination of the mainshock rupture to the harder patch along the Longmenshan fault to the north.

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Seismic Structure of Local Crustal Earthquakes beneath the Zipingpu Reservoir of Longmenshan Fault Zone

International Journal of Geophysics ◽

10.1155/2011/407673 ◽

2011 ◽

Vol 2011 ◽

pp. 1-6 ◽

Cited By ~ 1

Author(s):

Haiou Li ◽

Xiwei Xu ◽

Wentao Ma ◽

Ronghua Xie ◽

Jingli Yuan ◽

...

Keyword(s):

Fault Zone ◽

Three Dimensional ◽

P Wave ◽

The Tibetan Plateau ◽

Seismic Structure ◽

Infiltration Depth ◽

Low Velocity ◽

Longmenshan Fault Zone ◽

Velocity Models ◽

Longmenshan Fault

Three-dimensional P wave velocity models under the Zipingpu reservoir in Longmenshan fault zone are obtained with a resolution of 2 km in the horizontal direction and 1 km in depth. We used a total of 8589 P wave arrival times from 1014 local earthquakes recorded by both the Zipingpu reservoir network and temporary stations deployed in the area. The 3-D velocity images at shallow depth show the low-velocity regions have strong correlation with the surface trace of the Zipingpu reservoir. According to the extension of those low-velocity regions, the infiltration depth directly from the Zipingpu reservoir itself is limited to 3.5 km depth, while the infiltration depth downwards along the Beichuan-Yingxiu fault in the study area is about 5.5 km depth. Results show the low-velocity region in the east part of the study area is related to the Proterozoic sedimentary rocks. The Guanxian-Anxian fault is well delineated by obvious velocity contrast and may mark the border between the Tibetan Plateau in the west and the Sichuan basin in the east.

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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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Distinct tectonic activities in Guangxi, China due to large earthquakes on the Longmenshan fault zone

Physics of The Earth and Planetary Interiors ◽

10.1016/j.pepi.2020.106557 ◽

2020 ◽

Vol 307 ◽

pp. 106557

Author(s):

Huaizhong Yu ◽

Jing Zhao ◽

Xiaoxia Liu ◽

Chen Yu ◽

Chong Yue ◽

...

Keyword(s):

Fault Zone ◽

Longmenshan Fault Zone ◽

Longmenshan Fault ◽

Large Earthquakes ◽

Tectonic Activities

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Analysis of Spatiotemporal variations in mid-upper tropospheric methane during the Wenchuan Ms8.0 earthquake by three indices

10.5194/nhess-2018-342 ◽

2019 ◽

Author(s):

Jing Cui ◽

Xuhui Shen

Keyword(s):

Methane Concentration ◽

Vertical Direction ◽

Background Field ◽

Gradient Index ◽

Average Increase ◽

Longmenshan Fault Zone ◽

Deep Crust ◽

Distribution Features ◽

Before And After ◽

Longmenshan Fault

Abstract. This research studied the spatiotemporal variation in methane in the mid-upper troposphere during the Wenchuan earthquake (12 May, 2008) using AIRS retrieval data and discussed the methane anomaly mechanism. Three indices were proposed and used for analysis. Our results show that the methane concentration increased significantly in 2008, with an average increase of 5.12 * 10−8, compared to the average increase of 1.18 * 10−8 in the previous five years. The Alice and Diff indices can be used to identify methane concentration anomalies. The two indices showed that the methane concentration distribution before and after the earthquake broke the distribution features of the background field. As the earthquake approached, areas of high methane concentration gradually converged towards the west side of the epicenter from both ends of the Longmenshan fault zone. Moreover, a large anomalous area was centered at the epicenter eight days before the earthquake occurred, and a trend of strengthening, weakening and strengthening appeared over time. The Gradient index showed that the vertical direction obviously increased before the main earthquake, and the value was positive. The gradient value is negative during coseismic or postseismic events. The gradient index reflects the gas emission characteristics to some extent. We also determined that the methane release was connected with the deep crust-mantle stress state, as well as microfracture generation and expansion. However, due to the lack of any technical means to accurately identify the source and content of methane in the atmosphere before the earthquake, an in-depth discussion has not been conducted, and further studies on this issue may be needed.

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Seismic Potential Around the Northeastern Edge of the Longmenshan Fault Zone as Inferred from Seismological Observations

Pure and Applied Geophysics ◽

10.1007/s00024-019-02098-3 ◽

2019 ◽

Vol 177 (1) ◽

pp. 37-53 ◽

Cited By ~ 1

Author(s):

Reiken Matsushita ◽

Kazutoshi Imanishi ◽

Makiko Ohtani ◽

Yasuto Kuwahara ◽

Jiuhui Chen ◽

...

Keyword(s):

Fault Zone ◽

Longmenshan Fault Zone ◽

Seismic Potential ◽

Longmenshan Fault

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Research on Transverse Faults in the Longmenshan Fault Zone, China

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1010-1012.1380 ◽

2014 ◽

Vol 1010-1012 ◽

pp. 1380-1386

Author(s):

Wei Feng Wang ◽

Chuan Hua Zhu ◽

Yan Bin Qing ◽

Xin Jian Shan

Keyword(s):

Remote Sensing ◽

Fault Zone ◽

Field Studies ◽

Geophysical Data ◽

Remote Sensing Images ◽

Longmenshan Fault Zone ◽

Geomorphic Features ◽

Longmenshan Fault ◽

Regional Tectonic

The Longmenshan fault zone has been a research hotspot, but fewer scholars have paid attention to its transverse faults. According to the analysis of regional tectonic, seismic activities, geomorphic features, remote sensing images, and deep geophysical data, combined with field studies, the existence, distribution and type of the transverse faults in the Longmenshan fault zone were demonstrated. Research shows that there are 9 transverse faults that lie parallel to each other approximately at ~50km intervals in the Longmenshan fault zone. And transverse faults can be divided into regional transverse faults and localized transverse faults with NW strike, nearly EW strike and nearly SN strike.

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