Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity

被引:24
作者
Ayarza, P [1 ]
Juhlin, C
Brown, D
Beckholmen, M
Kimbell, G
Pechnig, R
Pevzner, L
Pevzner, R
Ayala, C
Bliznetsov, M
Glushkov, A
Rybalka, A
机构
[1] British Geol Survey, Reg Geophys Grp, Nottingham NG12 5GG, England
[2] Univ Salamanca, Fac Ciencias, Dept Geol, Area Geodinam, E-37008 Salamanca, Spain
[3] Uppsala Univ, Dept Earth Sci, S-75236 Uppsala, Sweden
[4] UralGeolKom, Bazhenov Geophys Expedit, Scheelit 624051, Sverdlovsk Dist, Russia
[5] Inst Ciencias Tierra Jaume Almera, Barcelona 08028, Spain
[6] Urals Geol Survey Expedit, UralGeolKom, Ekaterinburg 620000, Russia
[7] Rhein Westfal TH Aachen, D-52056 Aachen, Germany
关键词
D O I
10.1029/2000JB900137
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Near-vertical incidence reflection seismic data acquired in the Tagil Volcanic Are (Middle Urals) show the upper crust to be highly reflective. Two intersecting seismic lines located near the ongoing similar to 5400 m deep SG4 borehole show that the main reflectivity strikes approximately N-S and dips similar to 35 degrees-55 degrees to the east. Prominent reflections intercept the borehole at similar to 1000, similar to 1500, 2800-2900, similar to 3400, and between similar to 4000 and 5400 m, which correspond to intervals of low velocity/low density/low resistivity. The surface projections of these reflections lie parallel to the strike of magnetic anomaly trends. Multioffset vertical seismic profile (VSP) data acquired in the SG4 borehole show a seismic response dominated by P to S reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data Modeling of the VSP data constrains the depth at which reflectors intercept the borehole and suggests that the P to S conversions are best explained by low-velocity porous intervals rather than higher-velocity mafic material. The most prominent east dipping reflection on the surface seismic data is only imaged on VSP shots that sample the crust closer to the E-W seismic line. This discrepancy between the VSP and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector. Surface and borehole data suggest that the low-velocity/low-density/low-resistivity intervals are the most important source of reflectivity in the SG4 borehole area, although lithological contrasts may also play a role. Drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids. Tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and/or intrusions. Some of them might also represent high-porosity lava flows or pyroclastic units, common in island are environments.
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收藏
页码:21333 / 21352
页数:20
相关论文
共 44 条
[1]  
Aki K., 1980, QUANTITATIVE SEISMOL
[2]  
AYARZA P, 2000, IN PRESS J GEOL SOC
[3]   THE RELATIONSHIP BETWEEN SEISMIC VELOCITY AND DENSITY IN THE CONTINENTAL-CRUST - A USEFUL CONSTRAINT [J].
BARTON, PJ .
GEOPHYSICAL JOURNAL OF THE ROYAL ASTRONOMICAL SOCIETY, 1986, 87 (01) :195-208
[4]  
BASHTA EG, 1990, MIN GEOL SSSR, V1, P19
[5]  
BASHTA EG, 1996, EXPLOR PRESERV MINER, V7, P6
[6]   ANALYSES OF WAVE-FIELDS BY THE COMMON EXCITATION ARRAY (CEA) METHOD [J].
BLIZNETSOV, M ;
JUHLIN, C .
JOURNAL OF APPLIED GEOPHYSICS, 1994, 32 (2-3) :245-256
[7]   Crustal-scale structure and evolution of an arc-continent collision zone in the southern Urals, Russia [J].
Brown, D ;
Juhlin, C ;
Alvarez-Marron, J ;
Perez-Estaun, A ;
Oslianski, A .
TECTONICS, 1998, 17 (02) :158-170
[8]   ORIGIN OF REFLECTIONS FROM THE BREVARD FAULT ZONE [J].
CHRISTENSEN, NI ;
SZYMANSKI, DL .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH AND PLANETS, 1988, 93 (B2) :1087-1102
[9]   An analysis of shear waves observed in VSP data from the superdeep well at Kola, Russia [J].
Digranes, P ;
Kristoffersen, Y ;
Karajev, N .
GEOPHYSICAL JOURNAL INTERNATIONAL, 1996, 126 (02) :545-554
[10]  
DOKUCHAEV AY, 2000, IN PRESS EXPLOR PRES