Elastic wave velocities of the 2000m depth at Chinese Continental Scientific Drilling: Constraints on deep seismic reflection

Jin, Z. M., Ou, X. G., Xu, H. J., Kern, H., Jin, S. Y. and Hou, G. J. (2004) Elastic wave velocities of the 2000m depth at Chinese Continental Scientific Drilling: Constraints on deep seismic reflection Acta Petrologica Sinica, 20 (1). pp. 81-96.

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Abstract

The elastic wave velocities of 700 samples from main hole of Chinese Continental Scientific Drilling (CCSD) have been performed in the conditions of room temperature and pressure. The continuous section of seismic velocities (V-p and V-s) from 100m to 2000m was constructed, which provides an important petrophysical data for interpretation of geophysical model. Fresh eclogite yields the biggest compressional wave velocity (7.86km/s), and gneiss has smaller velocity (5.53 similar to 5.71 km/s). Seismic velocity of eclogite significantly decreases with increase of retrogressive metamorphism. Overall average V, velocity of main hole of 2000m rook is 6.2km/s which is correspondent to conclusion with high velocity zone (6.2 similar to 6.3 km/s) of the upper crust in Dabie-Sulu orogenic belt inferred from geophysical methods. Most rocks at the mail hole have pronounced seismic anisotropy. The velocity of V, and V, with water saturated rock increases by a factor of 19% and 10%, respectively. Conversely, anisotropy of Vp and Vs with water-saturated rock reduces 3% similar to 4%. Reflective coefficient (Rc) of different lithological boundaries is main factor producing seismic reflection. The lithological boundary between rutile-bearing eclogite and gneiss has the biggest reflective coefficient (0.24 similar to 0.31). Anisotropy and reflective strength is enhanced by mylonitic gneiss and foliated eclogite in ductile shear zone. Anisotropy and shear wave splitting of gneiss and eclogite are caused by the foliation of rocks, as confirmed by laboratory measurements under simulated in situ condition at high pressure and high temperature. Micro-cracks of rocks is closely related to in situ velocity variation. Velocities ( V, and V.) watersaturated rocks may represent in situ seismic velocity at main hole of the CCSD. The measurements of elastic wave velocities give an important constraints on the genesis of seismic reflector for this area.

Document Type: Article
Keywords: ultrahigh-pressure rock elastic wave velocity anisotropy seismic reflector CCSD Donghai fluid distribution anisotropy rocks crust zones belt dependence mylonites eclogites orogen
Research affiliation: Kiel University
ISSN: 1000-0569
Date Deposited: 24 Jan 2012 05:56
Last Modified: 08 Oct 2012 10:32
URI: http://eprints.uni-kiel.de/id/eprint/16136

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