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Book Chapter

Effects of Complex Tectonic Strain Observed in Two Multi-Component Multi-Azimuth VSPs from Pakistan

By
Alfred W. Stawicki
Alfred W. Stawicki
1Union Texas Pakistan, 3rd Floor, Bahria Complex, 24 Moulvi Tamizuddin Khan Road, GPO Box 3767. Karachi #2 Pakistan. Phone: 011 92 21 551 1194, 1195, 1196; Fax: 011 92 21 561 0634 .
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Heloise Bloxsom Lynn
Heloise Bloxsom Lynn
2Lynn Inc., 1646 Fall Valley Dr., Houston, TX 77077 USA. Phone: 713 556 9196; Fax: 713 497 6250.
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Published:
January 01, 1996

Abstract

In order to investigate the possibility of seismic velocity anisotropy within the lower Indus basin of Pakistan an experimental VSP was designed and recorded. Two offset VSPs were acquired utilizing an impulsive source during one common ascent of the sonde in a 7500 ft (2286 m) borehole. A “multi-pathing” phenomenon occurs at some depth levels which has been interpreted as a family of quasi-P waves. Hodogram analysis of the downgoing S-waves reveal similar families of q-S1 and q-S2 arrivals. At least two different mode conversion depths were identified for strong downgoing S-waves. Changes in the azimuth of the q-S1 arrivals versus depth were replicated on both offsets. The q-S1 polarizations are about 30-40 degrees clockwise to the fault azimuths and are interpreted to show the direction of fractures and maximum horizontal permeability. Strike-slip displacement is consistent with the geologic data, the q-S1 polarizations and the current knowledge concerning the intracratonic displacements on the Pak-lndian plate.

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Contents

Seismic Anisotropy

Erling Fjær
Erling Fjær
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Rune M. Holt
Rune M. Holt
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Jaswant S. Rathore
Jaswant S. Rathore
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Society of Exploration Geophysicists
ISBN electronic:
9781560802693
Publication date:
January 01, 1996

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