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https://doi.org/10.5194/se-2020-117
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-117
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Jul 2020

28 Jul 2020

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This preprint is currently under review for the journal SE.

Coseismic fluid–rock interactions in the Beichuan-Yingxiu surface rupture zone of the Mw 7.9 Wenchuan earthquake and its implication for the fault zone transformation

Yangyang Wang1, Xiaoqi Gao1, Sijia Li2, Shiyuan Wang3, Deyang Shi1,4, and Weibing Shen5 Yangyang Wang et al.
  • 1The Key Laboratory of Crustal Dynamics, Institute of Crustal Dynamics, China Earthquake Administration, Beijing, 100085, China
  • 2Geological Exploration and Development Research Institute, Chuanqing Drilling Engineering Co., Ltd., CNPC, Chengdu, Sichuan, 610500, China
  • 3Sichuan Earthquake Agency, Chengdu, 610041, China
  • 4Institute of Geophysics, China Earthquake Administration, Beijing, 100081, China
  • 5MLR Key Laboratory of Isotope Geology, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Abstract. Mechanism of fluids in modifying mineralogy and geochemistry of the fault zone and the role of rock-fluid interaction in the faulting weakening is still debatable. Through analyzing mineralogical compositions, major elements as well as micro-structural characteristics of outcrop samples including wall rocks, low damage zone, high damage zone and oriented fault gouge samples from principal slip zone gouges, mineralogical and geochemical variations of the fault-rocks is observed from Shaba outcrop of Beichuan-Yingxiu surface rupture zone of the Mw 7.9 Wenchuan earthquake, China. The element enrichment/depletion pattern of fault rock shows excellent consistency with the variation pattern of minerals in terms of the notable feldspar alteration and decomposition, decarbonization, coseismic illitization, and chloritization that occurs in the fault zone. The Isocon analysis indicates that the overall mass loss amount of the Shaba fault zone is ranked as low damage zone < high damage zone < fault gouge, while the mass removal within the fault gouge causes the greatest loss amount in the centeral strong-deformation region. The mechanism of material loss and transformation in the fault zone, analyzed by comprehensive study, is found to be complicated: (1) during the coseismic period, the mechanical fracturing, the dehydration reaction and thermal pressurization are likely the main factors; (2) during the postseismic period, infiltration by the postseismic hydrothermal fluids is the key factor. Therefore, the coseismic mechanical fracturing, chemical reaction related to coseismic frictional heating, and postseismic fuild-rock interaction are important factors to change and control the material composition and the fault zone evolution.

Yangyang Wang et al.

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Short summary
The 2008 Wenchuan Earthquake (Mw 7.9) in China had never occurred since the beginning of the recorded history of the world. The continuous variation of mineral assemblages and major element contents in the fault zone was observed. Significant fuild-rock interaction occurred in the fault zone and leaded to variation of mechanism of material loss in the fault zone with time and space. This study has important significance and provides an example for investigation of coseismic fluid action.
The 2008 Wenchuan Earthquake (Mw 7.9) in China had never occurred since the beginning of the...
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