Crustal and upper mantle velocity structure determination using inversion methods

مرکز و کتابخانه مطالعات اسلامی به زبان های اروپایی

منو

" Crustal and upper mantle velocity structure determination using inversion methods "
A. Ibenbrahim J. F. Ni

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112704
Doc. No	:	TLpq303843213
Main Entry	:	A. Ibenbrahim
	:	J. F. Ni
Title & Author	:	Crustal and upper mantle velocity structure determination using inversion methods\ A. IbenbrahimJ. F. Ni
College	:	New Mexico State University
Date	:	1990
student score	:	1990
Degree	:	Ph.D.
Page No	:	216
Abstract	:	In the first part of this dissertation an iterative source equalization method was introduced to extend previous methods which approximated the vertical receiver function by a delta function, and used this approximation to remove the source effects from seismograms. For short-period data the above approximation is not sufficient, instead we estimate the entire vertical receiver function and use it to obtain a better approximation of the source effects. In the second part of this dissertation the iterative method of Part I was applied to invert for the shear-wave receiver structure beneath the Albuquerque station. The results reveal the existence of an upper crustal low shear-wave velocity zone (LVZ). This LVZ can be attributed to the presence of either water or magma bodies. The lower crust is also characterized by a LVZ that extends from a 20-34 km depth. We suggest that this LVZ is due to magma bodies within a 26-30 km depth range. Our results indicate that the Moho is at a 46 km depth and consists of a 4 km transitional zone. In the third part of this dissertation P- and S-wave travel time data were used to simultaneously invert for velocity structures and hypocenters beneath the Tarbela seismic network, which is situated in the western Hazara Arc, Pakistan. We find that the eastern part of the Hazara-Kashmir Syntaxis is underlain by a low velocity zone which we interpreted as a former foreland basin covered by late-stage southeasterly directed thrust sheets. North of the Hazara Thrust Zone (HTZ), the velocity structures indicate that the underthrusting Indian Plate dips gently to the northeast with an increased slope of 5 to 8 until it reaches the NW trending Indus-Kohistan Seismic Zone (IKSZ). Along the IKSZ the Indian Plate bends more steeply to the northeast. The IKSZ appears to consist of two distinct seismic zones separated by a 4 km thick aseismic region. This aseismic zone may indicate an upper crustal detachment. The lower IKSZ is wedge shaped and may represent the leading edge of a southwestward directed basement slab which has not yet ruptured the surface.
Subject	:	Earth sciences
	:	Geophysics
	:	Peshawar Basin
	:	Rio Grande Rift
	:	velocity structure