S-wave crustal and upper mantle’s velocity structure in the eastern Tibetan Plateau — Deep environment of lower crustal flow

Wang, Chunyong; Lou, Hai; Lü, Zifeng; Wu, Jianping; Chang, Ling; Dai, Shigui; You, Hongjian; Fang-tou, Tang; Zhu, Lupei; Silver, Paul G.

doi:10.1007/s11430-008-0008-5

Cited by 43 publications

(34 citation statements)

References 34 publications

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“…On both sides of the Longmenshan fault zone, the crustal thickness varies from 35 km in the east Sichuan Basin to 70 km in the west. A variety of geophysical factors demonstrated strong gradient changes on LFZ sides, such as electrical structure [4], gravity field [5], seismic wave attenuation [6], and P-wave velocity structure [7].…”

Section: Tectonic Backgroundmentioning

confidence: 99%

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

2013

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The source rupture process of the M S 7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations. Results reveal that the rupture process of the Lushan M S 7.0 event to be simpler than that of the Wenchuan earthquake and also showed significant differences between the two rupture processes. The whole rupture process lasted 36 s and most of the moment was released within the first 13 s. The total released moment is 1.9×10 19 N m with M W =6.8. Rupture propagated upwards and bilaterally to both sides from the initial point, resulting in a large slip region of 40 km×30 km, with the maximum slip of 1.8 m, located above the initial point. No surface displacement was estimated around the epicenter, but displacement was observed about 20 km NE and SW directions of the epicenter. Both showed slips of less than 40 cm. The rupture suddenly stopped at 20 km NE of the initial point. This was consistent with the aftershock activity. This phenomenon indicates the existence of significant variation of the medium or tectonic structure, which may prevent the propagation of the rupture and aftershock activity. The earthquake risk of the left segment of Qianshan fault is worthy of attention. . The early rupturing stage showed reverse faulting and later changed to right-lateral strike slip faulting, leaving 2 large slip areas along the LFZ on the surface. Aftershock activity also showed a unilateral pattern along the northeastern direction, consistent with the direction of rupture propagation. These seismological results were in accordance with the results of the post-earthquake investigation and of observations made during the disaster [2,3]. Evaluation of the source-rupture process using the digital seismic waveform data can provide information about the rupture scale, the way the fault moves, and the slip distribution on the fault within several hours of a strong earthquake. These estimations not only provide information regarding the seriously damaged areas and the way of dislocation but also information suitable for estimation of the scale of destruction and planning of rescue work. It can also provide information regarding the activity of the causative fault, the

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Section: Tectonic Backgroundmentioning

confidence: 99%

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

2013

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“…Geophysical studies have revealed its low-velocity and low-resistivity features within the mid-lower crust [10][11][12][13][14] and they are indicative of deep dynamics of the eastern Tibetan Plateau. The slow Pn-wave velocity indicates again that the Songpan-Ganzi mountain range has a weak lithospheric mantle with low rheologic strength, so that ductile deformation probably happens not only in the mid-lower crust but also in the uppermost mantle.…”

Section: Pn-wave Velocitymentioning

confidence: 99%

“…Actually, this boundary, reveled by the velocity and resistivity variation, extends throughout the crust and the upper mantle [10][11][12][13][14][15][16][17]. It plays a prominent role in dynamic process of controlling tectonic evolution of the Songpan-Ganzi mountain range and the Sichuan basin.…”

Section: Pn-wave Velocitymentioning

confidence: 99%

“…Crustal shortening occurred mainly in the vertical direction. As the result, the upper crust in the Longmen Mountain region overrides on the foreland basin along thrust faults, the mountains are greatly elevated; the mid-lower crust with the low-velocity and low-resistivity features is thickened by ductile deformation [10][11][12][13][14]; the crustal thickness is increased from 40-42 km in the Sichuan basin to 55-60 km in the Songpan-Ganzi mountain range [23,24]. Therefore, the velocity boundary along the Longmenshan fault appears as a transition belt of the lithospheric strength between the Songpan-Ganzi mountain range and the Sichuan basin [8].…”

Section: Pn-wave Velocitymentioning

confidence: 99%

“…The M s 8.0 earthquake in Wenchuan and most aftershocks occurred on its eastern margin [9][10][11]. Although the surface rupture of the main shock is localized along the Beichuan-Yingxiu fault, its deep mechanism is related to the ductile deformation of the low-velocity and low-resistivity zone in the mid-lower crust and also related to the partial upwelling in the upper mantle [10][11][12][13][14][15]. They provide dynamic sources for stress accumulation, fault displacement, and seismic rupture within the crust.…”

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Pn-wave velocity and anisotropy of the western Sichuan and Longmen Mountain region, China

Xu¹,

Li²,

Huang

et al. 2010

Sci. China Earth Sci.

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Pn-wave velocity and anisotropy beneath the western Sichuan and adjacent region are inverted by a tomography method using arrival data from earthquakes recorded by the Sichuan Earthquake Network. It is followed by an analysis of the uppermost mantle structure of the Longmen Mountain region and the deep tectonics of the M s 8.0 earthquake in Wenchuan. Our results reveal a prominent velocity contrast across the Longmenshan fault: low velocities in the Songpan-Ganzi mountain range and high velocities in the Sichuan basin. They indicate that the Songpan-Ganzi mountain range is underlain by a weak uppermost mantle, which is easy to create ductile flow, whereas the Sichuan basin has a mechanically strong uppermost mantle. These features reflect a difference of the lithospheric mantle beneath tectonically active mountain range and stable basin. The boundary between the high and low velocities is coincident with the Longmenshan fault. Bordered by Wenchuan, the northern part of the boundary is parallel to the fault belt and aftershock distribution, but the southern part of the boundary deviates from the fault belt and is bent toward the Sichuan basin. The M s 8.0 earthquake in Wenchuan is located at the flexural part between them, where a strong heterogeneity is shown in the velocity variation across and parallel to the boundary. This area is reasonably believed as a potential location for regional stress accumulation and release in the Longmen Mountain region, reflecting a prominent character in the deep structure around Wenchuan. Pn-wave anisotropy reveals the mantle flow that is consistent with the eastward movement of the Tibetan Plateau. This process provided deep dynamic sourse for tectonic deformation in the Longmen Mountain region and for the occurrence of the Wenchuan M s 8.0 earthquake, but it is clearly affected by the strong lithosphere of the Sichuan basin. There is no correlation between the Pn-wave anisotropy and the Longmenshan fault, hence, this fault system is only restricted within the crust. However, the mantle flow beneath the southeastern Tibetan Plateau shows a clockwise rotation along the Xianshuihe fault. We infer that these two fault systems may be controlled by different deep dynamics. western Sichuan, Longmen Mountain, Pn velocity, anisotropy, Wenchuan earthquake Citation: Xu Y, Li Z W, Huang R Q, et al. Pn-wave velocity and anisotropy of the western Sichuan and Longmen

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Hydraulic properties of samples retrieved from the Wenchuan earthquake Fault Scientific Drilling Project Hole‐1 (WFSD‐1) and the surface rupture zone: Implications for coseismic slip weakening and fault healing

Chen

Yang

et al. 2016

Geochem Geophys Geosyst

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In this study, we report the hydraulic properties of samples recovered from the first borehole of the Wenchuan earthquake Fault Scientific Drilling and from outcrops associated with the surface rupture zone of the 2008 Wenchuan earthquake. Compositional and microstructural analyses have also been performed on selected samples. Using the pore pressure oscillation method, the permeability measurements show that (1) fault gouge samples have low permeabilities, decreasing from 2 3 10 218 m 2 at an effective pressure (P e ) of 10 MPa (equivalent to an in situ depth of 600 m) to 9 3 10 221 m 2 at 155 MPa. (2) Intact and cemented samples are impermeable with permeabilities less than 2 3 10 220 m 2 at 10 MPa. (3) Fractured samples have variable permeabilities, ranging from 3 3 10 215 to 1 3 10 220 m 2 at 10 MPa, and are most insensitive to changes in the effective pressure. (4) Granitic cataclasites have a moderate permeability at low pressure (i.e., 10 216 to 10 217 m 2 at 10 MPa); which decreases rapidly with increasing P e . Hydraulic conduction of the fault is believed to be influenced by the permeability of the fractures developed, which is controlled by the density, aperture, and/or connectivity of the fractures. Microstructural and compositional analyses of the samples indicate that the fault zone heals through chemically mediated fracture closure related to mineral precipitation, possibly assisted by pressure solution of stressed fracture asperities. Although other weakening mechanisms remain possible, our laboratory measurements combined with numerical modeling reveal that thermal/thermochemical pressurization, perhaps leading to gouge fluidization, played an important role in the dynamic weakening of the Wenchuan earthquake, at least in the study area.

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S-wave crustal and upper mantle’s velocity structure in the eastern Tibetan Plateau — Deep environment of lower crustal flow

Cited by 43 publications

References 34 publications

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

Pn-wave velocity and anisotropy of the western Sichuan and Longmen Mountain region, China

Hydraulic properties of samples retrieved from the Wenchuan earthquake Fault Scientific Drilling Project Hole‐1 (WFSD‐1) and the surface rupture zone: Implications for coseismic slip weakening and fault healing

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