Structural heterogeneity of the Longmenshan fault zone and the mechanism of the 2008 Wenchuan earthquake (Ms 8.0)

ABSTRACT We use the eikonal equation-based seismic travel-time tomography method to image the source areas of the 2008 Wenchuan earthquake and the 2013 Lushan earthquake in the Longmenshan fault zone. High-resolution VP and VS models are obtained by inverting 75,686 P-wave and 74,552 S-wave travel times of local earthquakes during the period from 2009 to 2018. The tomographic models reveal strong crustal velocity heterogeneities in the study area. A significant velocity contrast exists across the Longmenshan fault zone: The western Songpan–Ganzi block is a high-velocity body, whereas the eastern Sichuan basin is a low-velocity anomaly. The hypocenter of the 2008 Wenchuan earthquake is between a high-velocity and a low-velocity anomaly. Beneath the Wenchuan mainshock, there is a significant low-velocity structure in the lower crust. The 2013 Lushan earthquake occurred in rocks associated with a high-velocity anomaly. A distinct low-velocity zone with low seismicity is imaged between the 2008 Wenchuan earthquake and the 2013 Lushan earthquake, where the crustal ductile deformation is likely to occur. The Baoxing complex to the northwest of the Lushan hypocenter exhibits as a high-velocity anomaly, which may be a carrier of stress accumulation and more prone to seismic activities in the future.

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High-resolution lithosphere viscosity structure and the dynamics of the 2008 Wenchuan earthquake area: new constraints from magnetotelluric imaging

Geophysical Journal International ◽

10.1093/gji/ggaa214 ◽

2020 ◽

Vol 222 (2) ◽

pp. 1352-1362

Author(s):

Tao Zhu ◽

Yan Zhan ◽

Martyn Unsworth ◽

Guoze Zhao ◽

Xiangyu Sun

Keyword(s):

Tibetan Plateau ◽

Wenchuan Earthquake ◽

Fault Zone ◽

Crustal Deformation ◽

Small Scale ◽

Longmenshan Fault Zone ◽

2008 Wenchuan Earthquake ◽

Longmenshan Fault ◽

Lateral Variations ◽

Earthquake Area

SUMMARY Estimation of lithospheric viscosity remains challenging, especially for variations with spatial scales less than 100 km. Some recent studies have developed a method to determine viscosity structure from electrical conductivity models determined from magnetotelluric (MT) data. This method was initially applied to the extensional transition zone from the Great Basin to Colorado Plateau. Here, we use this approach to infer the effective lithospheric viscosity in a convergent setting by using an MT profile that crosses the eastern margin of the Tibetan Plateau. The profile extends from the Songpan-Ganzi block, crosses the 2008 Wenchuan earthquake epicentre region and ends in the Sichuan basin. The preferred viscosity structure is characterized by the middle-lower crustal viscosities in the range 2.42 × 1018 to 2.69 × 1021 Pa s below the Songpan-Ganzi block. In the Longmenshan fault zone and 2008 Wenchuan Ms8.0 earthquake area, the crustal viscosity is higher and in the range 4.32 × 1018 to 5.10 × 1021 Pa s with significant small-scale (<100 km) lateral variations. The MT-derived viscosities are consistent with previous regional-scale estimates but reveal the viscosity structure in more detail. The preferred geodynamic model can explain both the crustal deformation velocity and the small-scale lateral variations of surface topography. It implies that the crustal deformation is driven by mantle flow that results in a weak coupling of the upper and middle-lower crust beneath the eastern Tibetan Plateau. The inferred viscosity structure may help further understand the earthquake mechanisms in the Longmenshan fault zone.

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Structures and high-velocity frictional properties of the Pingxi fault zone in the Longmenshan fault system, Sichuan, China, activated during the 2008 Wenchuan earthquake

Tectonophysics ◽

10.1016/j.tecto.2013.04.011 ◽

2013 ◽

Vol 599 ◽

pp. 135-156 ◽

Cited By ~ 32

Author(s):

Lu Yao ◽

Shengli Ma ◽

Toshihiko Shimamoto ◽

Tetsuhiro Togo

Keyword(s):

Wenchuan Earthquake ◽

Fault Zone ◽

High Velocity ◽

Fault System ◽

2008 Wenchuan Earthquake ◽

Frictional Properties ◽

The 2008 Wenchuan Earthquake ◽

Longmenshan Fault System ◽

Longmenshan Fault

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Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 1. Signatures within the Deep Wenchuan Earthquake Fault Zone and Their Implications

Minerals ◽

10.3390/min8090385 ◽

2018 ◽

Vol 8 (9) ◽

pp. 385 ◽

Cited By ~ 4

Author(s):

Li-Wei Kuo ◽

Jyh-Rou Huang ◽

Jiann-Neng Fang ◽

Jialiang Si ◽

Haibing Li ◽

...

Keyword(s):

Wenchuan Earthquake ◽

Fault Zone ◽

Active Fault ◽

Carbonaceous Materials ◽

Coseismic Slip ◽

Earthquake Fault ◽

Active Fault Zone ◽

2008 Wenchuan Earthquake ◽

Seismic Slip ◽

Longmenshan Fault

Graphitization of carbonaceous materials (CM) has been experimentally demonstrated as potential evidence of seismic slip within a fault gouge. The southern segment of the Longmenshan fault, a CM-rich-gouge fault, accommodated coseismic slip during the 2008 Mw 7.9 Wenchuan earthquake and potentially preserves a record of processes that occurred on the fault during the slip event. Here, we present a multi-technique characterization of CM within the active fault zone of the Longmenshan fault from the Wenchuan earthquake Fault Scientific Drilling-1. By contrast with field observations, graphite is pervasively and only distributed in the gouge zone, while heterogeneously crystallized CM are present in the surrounding breccia. The composite dataset that is presented, which includes the localized graphite layer along the 2008 Wenchuan earthquake principal slip zone, demonstrates that graphite is widely distributed within the active fault zone. The widespread occurrence of graphite, a seismic slip indicator, reveals that surface rupturing events commonly occur along the Longmenshan fault and are characteristic of this tectonically active region.

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