The active tectonics and structure of the Eastern Himalayan Syntaxis and surrounding regions.

Persistent Link:
http://hdl.handle.net/10150/184802
Title:
The active tectonics and structure of the Eastern Himalayan Syntaxis and surrounding regions.
Author:
Holt, William Everett.
Issue Date:
1989
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
I determined the source parameters of 53 moderate-sized earthquakes in the region of the Eastern Himalayan Syntaxis through the joint inversion of regional and teleseismic distance long-period body waves. The average rates of deformation are determined by summing the moment tensors from both recent and historic earthquakes. Strike-slip movement on the Sagaing fault terminates in the north (just south of the syntaxis), where thrusting (northeast convergence) and crustal thickening are predominant. Slip vectors for thrust mechanisms in the Eastern Himalaya in general are not orthogonal to the Himalayan mountain front but show an oblique component of slip. A combination of thrust and strike-slip faulting (Molnar and Deng, 1984) for the great 1950 Assam earthquake is consistent with the rates of underthrusting in the entire Himalaya and the rate of spreading in Tibet (assuming that a 1950-type earthquake recurs every 400 years). An estimated 4-21 mm/yr of right-lateral motion between southeast Asia and the Burma subplate is absorbed within the zone of distributed shear between the Sagaing and Red River faults. A component of westward motion (3-7 mm/yr) of the western boundary of the distributed shear zone may cause some of the late Cenozoic compression and folding in the northern Indoburman Ranges. Distributed shear and clockwise rotation of blocks is also occurring in Yunnan north of the Red River Fault. The inversion of 130 regional distancewaveforms for average crustal thickness and upper mantle Pn velocity indicates an increase in Pn velocity, coincident with increase in crustal thickness, of about 0.20 km/s beneath the Tibetan Plateau. Impulsive Pn arrivals from paths that cross the Tibetan Plateau can be modeled with a positive upper mantle velocity gradient, indicating an upper mantle lid approximately 100-km-thick beneath southern Tibet. This "shield-like" structure supports a model in which Indian continental lithosphere has underthrust Tibet. The crustal shortening within Tibet 8 mm/yr is thus viewed as an upper crustal phenomenon in which the faults do not penetrate the deep crust or upper Mantle. The forces generated by the thick crust in Tibet may partly cause the strike-slip faulting and east-west convergence in Sichuan and the movement of upper crustal blocks in Yunnan.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Plate tectonics -- Himalaya Mountains.; Geology -- Himalaya Mountains.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Wallace, Terry C.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleThe active tectonics and structure of the Eastern Himalayan Syntaxis and surrounding regions.en_US
dc.creatorHolt, William Everett.en_US
dc.contributor.authorHolt, William Everett.en_US
dc.date.issued1989en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractI determined the source parameters of 53 moderate-sized earthquakes in the region of the Eastern Himalayan Syntaxis through the joint inversion of regional and teleseismic distance long-period body waves. The average rates of deformation are determined by summing the moment tensors from both recent and historic earthquakes. Strike-slip movement on the Sagaing fault terminates in the north (just south of the syntaxis), where thrusting (northeast convergence) and crustal thickening are predominant. Slip vectors for thrust mechanisms in the Eastern Himalaya in general are not orthogonal to the Himalayan mountain front but show an oblique component of slip. A combination of thrust and strike-slip faulting (Molnar and Deng, 1984) for the great 1950 Assam earthquake is consistent with the rates of underthrusting in the entire Himalaya and the rate of spreading in Tibet (assuming that a 1950-type earthquake recurs every 400 years). An estimated 4-21 mm/yr of right-lateral motion between southeast Asia and the Burma subplate is absorbed within the zone of distributed shear between the Sagaing and Red River faults. A component of westward motion (3-7 mm/yr) of the western boundary of the distributed shear zone may cause some of the late Cenozoic compression and folding in the northern Indoburman Ranges. Distributed shear and clockwise rotation of blocks is also occurring in Yunnan north of the Red River Fault. The inversion of 130 regional distancewaveforms for average crustal thickness and upper mantle Pn velocity indicates an increase in Pn velocity, coincident with increase in crustal thickness, of about 0.20 km/s beneath the Tibetan Plateau. Impulsive Pn arrivals from paths that cross the Tibetan Plateau can be modeled with a positive upper mantle velocity gradient, indicating an upper mantle lid approximately 100-km-thick beneath southern Tibet. This "shield-like" structure supports a model in which Indian continental lithosphere has underthrust Tibet. The crustal shortening within Tibet 8 mm/yr is thus viewed as an upper crustal phenomenon in which the faults do not penetrate the deep crust or upper Mantle. The forces generated by the thick crust in Tibet may partly cause the strike-slip faulting and east-west convergence in Sichuan and the movement of upper crustal blocks in Yunnan.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectPlate tectonics -- Himalaya Mountains.en_US
dc.subjectGeology -- Himalaya Mountains.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorWallace, Terry C.en_US
dc.contributor.committeememberChase, Clem G.en_US
dc.contributor.committeememberRichardson, Randall M.en_US
dc.contributor.committeememberJohnson, Roy A.en_US
dc.identifier.proquest9003484en_US
dc.identifier.oclc703255658en_US
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