VRANCEA'99 is a seismic refraction line that was carried out in 1999 to investigate the deep structure and physical properties of the upper lithosphere of the southeastern Carpathians and its foreland. It runs from the city of Bacau to the Danube River, traversing the Vrancea epicentral area of strong intermediate-depth seismicity and the city of Bucharest. Interpretation of P-wave arrivals led to a velocity model that displays a multi-layered crust with velocities increasing with depth. The range of P wave velocities in the sedimentary cover increases from N to S and a structuring of the autochthonous basement of the Moesian Platform is observed. The crystalline crust displays thickness variations, but at the same time the lateral velocity structure along the seismic line remains almost constant. An intra-crustal boundary separates an upper crust from the lower crust. Within the upper mantle a low velocity zone is detected at a depth of about 55-km. The interpretation of observable S-waves resulted in a velocity model that shows the same multi-layered crust, with S-velocities increasing similarly with depth as the P-waves. The corresponding Poisson's ratio is highly variable throughout the crust and ranges from 0.20-0.35 for the sedimentary cover to 0.22-0.25 for the crystalline crust. The interpretation of the V-p, V-s and Poisson's ratio in petrological terms suggests a large variety of rocks from sand and clay to sandstone, limestone and dolomite within the sedimentary cover. Within the crystalline crust the most probably rock types are granite, granodiorite, granite-gneiss and/or felsic, amphibolite-gneiss in the upper part and gneiss and /or amphibolite in the lower part. Based on the 2-D seismic velocity model, a density model is developed. Density values are assigned to each layer in agreement with the P-wave velocity model and with values accepted for the geological units in the area. After several iterations a good fit between the computed and observed Bouguer anomalies was obtained along the seismic line. (c) 2005 Elsevier B.V. All rights reserved.
机构:
State Key Laboratory of Geodesy and Earth’s Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of SciencesInstitute of Geology and Geophysics, Chinese Academy of Sciences
Sidao Ni
Jun Xie
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Mengcheng National Geophysical Observatory, School of Earth and Space Sciences, University of Science and Technology of ChinaInstitute of Geology and Geophysics, Chinese Academy of Sciences
Jun Xie
Yingjie Xia
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Mengcheng National Geophysical Observatory, School of Earth and Space Sciences, University of Science and Technology of ChinaInstitute of Geology and Geophysics, Chinese Academy of Sciences
Yingjie Xia
Xiangfang Zeng
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CAS Key Laboratory of Computational Geodynamics,University of Chinese Academy of SciencesInstitute of Geology and Geophysics, Chinese Academy of Sciences
Xiangfang Zeng
Bin Liu
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Mengcheng National Geophysical Observatory, School of Earth and Space Sciences, University of Science and Technology of ChinaInstitute of Geology and Geophysics, Chinese Academy of Sciences
机构:
Univ Tokyo, Earthquake Res Inst, Tokyo 113, Japan
Univ Hawaii Manoa, SOEST, Honolulu, HI 96814 USAUniv Tokyo, Earthquake Res Inst, Tokyo 113, Japan
Arai, Ryuta
Iwasaki, Takaya
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Univ Tokyo, Earthquake Res Inst, Tokyo 113, JapanUniv Tokyo, Earthquake Res Inst, Tokyo 113, Japan
Iwasaki, Takaya
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Sato, Hiroshi
Abe, Susumu
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JGI Inc, Tokyo, JapanUniv Tokyo, Earthquake Res Inst, Tokyo 113, Japan
Abe, Susumu
Hirata, Naoshi
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Univ Tokyo, Earthquake Res Inst, Tokyo 113, JapanUniv Tokyo, Earthquake Res Inst, Tokyo 113, Japan