Magnetotelluric Constraints on the Occurrence of Lower Crustal Earthquakes in the Intra-plate Setting of Central Indian Tectonic Zone
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MT data presented in this study were acquired under the Council of Scientific & Industrial Research (CSIR) Network Project SMM004. Data modeling and interpretation were carried out under MLP-6104-28 (BPK). Thanks are given to Dr. Ch. Mohan Rao, Director, CSIR-National Geophysical Research Institute, Hyderabad, for his kind consent to publish this work.


Magnetotelluric Constraints on the Occurrence of Lower Crustal Earthquakes in the Intra-plate Setting of Central Indian Tectonic Zone
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MT data presented in this study were acquired under the Council of Scientific & Industrial Research (CSIR) Network Project SMM004. Data modeling and interpretation were carried out under MLP-6104-28 (BPK). Thanks are given to Dr. Ch. Mohan Rao, Director, CSIR-National Geophysical Research Institute, Hyderabad, for his kind consent to publish this work.

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    摘要:

    Lower crustal earthquake occurrence in the Central Indian Tectonic Zone (CITZ) of the Indian sub-continent was investigated using magnetotelluric (MT) data. MT models across the CITZ, including the new resistivity model across the 1938 Satpura lower crustal earthquake epicenter, show low resistive (<80 ?m) mid-lower crust and infer small volume (<1 vol%) of aqueous fluids existing in most part of lower crust. This in conjunction with xenoliths and other geophysical data supports a predominant brittle/semi-brittle lower crustal rheology. However, the local deep crustal zones with higher fluid content of 2.2%–6.5% which have been mapped imply high pore pressure conditions. The observation above and the significant strain rate in the region provide favorable conditions (strong/moderate rock strength, moderate temperature, high pore pressure and high strain rate) for brittle failure in the lower crust. It can be inferred that the fluid-rich pockets in the mid-lower crust might have catalyzed earthquake generation by acting as the source of local stress (fluid pressure), which together with the regional stress produced critical seismogenic stress conditions. Alternatively, fluids reduce the shear strength of the rocks to favor tectonic stress concentration that can be transferred to seismogenic faults to trigger earthquakes.

    Abstract:

    Lower crustal earthquake occurrence in the Central Indian Tectonic Zone (CITZ) of the Indian sub-continent was investigated using magnetotelluric (MT) data. MT models across the CITZ, including the new resistivity model across the 1938 Satpura lower crustal earthquake epicenter, show low resistive (<80 ?m) mid-lower crust and infer small volume (<1 vol%) of aqueous fluids existing in most part of lower crust. This in conjunction with xenoliths and other geophysical data supports a predominant brittle/semi-brittle lower crustal rheology. However, the local deep crustal zones with higher fluid content of 2.2%–6.5% which have been mapped imply high pore pressure conditions. The observation above and the significant strain rate in the region provide favorable conditions (strong/moderate rock strength, moderate temperature, high pore pressure and high strain rate) for brittle failure in the lower crust. It can be inferred that the fluid-rich pockets in the mid-lower crust might have catalyzed earthquake generation by acting as the source of local stress (fluid pressure), which together with the regional stress produced critical seismogenic stress conditions. Alternatively, fluids reduce the shear strength of the rocks to favor tectonic stress concentration that can be transferred to seismogenic faults to trigger earthquakes.

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K. K. ABDUL AZEEZ.2016. Magnetotelluric Constraints on the Occurrence of Lower Crustal Earthquakes in the Intra-plate Setting of Central Indian Tectonic Zone[J]. ACTA GEOLOGICA SINICA(English edition),90(3):884~899

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  • 收稿日期:2014-12-01
  • 最后修改日期:2015-06-05
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  • 在线发布日期: 2016-06-21
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