Constraining the far-field maximum horizontal stress in the plate tectonic area

In orogenic belts, the far-field horizontal stresses of tectonic origin often control the stress regime in the nearby regions. However, due to the non-uniform convergence of the tectonic plates, the far-field horizontal stresses show local variation. The syntaxial bends in the orogenic belts are are...

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Main Author:	Ali, Wahid
Format:	Thesis
Language:	English
Published:	2022
Subjects:	TA Engineering (General) Civil engineering (General)
Online Access:	http://eprints.utm.my/102862/1/WahidAliPSKA2022.pdf.pdf
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id	my-utm-ep.102862
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spelling	my-utm-ep.1028622023-09-26T06:01:19Z Constraining the far-field maximum horizontal stress in the plate tectonic area 2022 Ali, Wahid TA Engineering (General). Civil engineering (General) In orogenic belts, the far-field horizontal stresses of tectonic origin often control the stress regime in the nearby regions. However, due to the non-uniform convergence of the tectonic plates, the far-field horizontal stresses show local variation. The syntaxial bends in the orogenic belts are areas where the orientation of far-field maximum horizontal stress shows marked deviation from the general trend of the plate movement. The Hazara Kashmir Syntaxis (HKS), located in the western Himalayas, is one such structure where the major crustal-scale faults are making a loop. This looping of the thrust faults makes it difficult to constrain the orientation of the far-field horizontal stresses in the core of the HKS. The Neelum Jhelum Hydropower Project’s (NJHP) headrace tunnel traversing the core of the HKS revealed important information regarding the bedrock geology and in-situ stress state in the syntaxis. This information has not been previously used for constraining the far-field horizontal stresses in the area. The purpose of this study is to constrain the far-field horizontal stress in the HKS based on field observations and the geological and geotechnical data collected during the excavation of the headrace tunnel. The study utilised 3D finite element modelling approach to examine the complex interaction among the gravitational stresses due to current topography, exhumation-induced remnant stresses, excavation-induced perturbations, and far-field horizontal stresses. The simulated results were compared with the measured in-situ stresses for model validation. The simulation results demonstrated that the orientation and magnitude of gravitational principal and horizontal stresses at shallow depths are largely controlled by the current topography. The addition of the exhumation-induced gravitational remnant stresses caused changes in the orientation and magnitude of the principal stresses. However, the orientation of the maximum horizontal stress (SH) was less affected. The SH was also found to be less perturbed by the tunnel excavation. In the subsequent analysis, the models were compressed using horizontal straining from different directions to get SH magnitude and orientation similar to the measured SH. The results showed that the modelled SH orientation at the different monitoring points could be achieved by applying different magnitudes of horizontal straining. These results suggested that the 0° Model with east-west directed maximum straining shows SH trends consistent with the measured SH trends. The east-west directed far-field horizontal stress derived during this study is consistent with the local movement direction of the Main Boundary Thrust (MBT) fault in the study area. The study revealed that the SH orientation is a better candidate for constraining the far-field horizonal stresses. Moreover, the study revealed that the local variation in the strike of MBT causes local variations in the orientation of far-field horizontal stresses in the HKS. 2022 Thesis http://eprints.utm.my/102862/ http://eprints.utm.my/102862/1/WahidAliPSKA2022.pdf.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:150565 phd doctoral Universiti Teknologi Malaysia Faculty of Engineering - School of Civil Engineering
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	TA Engineering (General) Civil engineering (General)
spellingShingle	TA Engineering (General) Civil engineering (General) Ali, Wahid Constraining the far-field maximum horizontal stress in the plate tectonic area
description	In orogenic belts, the far-field horizontal stresses of tectonic origin often control the stress regime in the nearby regions. However, due to the non-uniform convergence of the tectonic plates, the far-field horizontal stresses show local variation. The syntaxial bends in the orogenic belts are areas where the orientation of far-field maximum horizontal stress shows marked deviation from the general trend of the plate movement. The Hazara Kashmir Syntaxis (HKS), located in the western Himalayas, is one such structure where the major crustal-scale faults are making a loop. This looping of the thrust faults makes it difficult to constrain the orientation of the far-field horizontal stresses in the core of the HKS. The Neelum Jhelum Hydropower Project’s (NJHP) headrace tunnel traversing the core of the HKS revealed important information regarding the bedrock geology and in-situ stress state in the syntaxis. This information has not been previously used for constraining the far-field horizontal stresses in the area. The purpose of this study is to constrain the far-field horizontal stress in the HKS based on field observations and the geological and geotechnical data collected during the excavation of the headrace tunnel. The study utilised 3D finite element modelling approach to examine the complex interaction among the gravitational stresses due to current topography, exhumation-induced remnant stresses, excavation-induced perturbations, and far-field horizontal stresses. The simulated results were compared with the measured in-situ stresses for model validation. The simulation results demonstrated that the orientation and magnitude of gravitational principal and horizontal stresses at shallow depths are largely controlled by the current topography. The addition of the exhumation-induced gravitational remnant stresses caused changes in the orientation and magnitude of the principal stresses. However, the orientation of the maximum horizontal stress (SH) was less affected. The SH was also found to be less perturbed by the tunnel excavation. In the subsequent analysis, the models were compressed using horizontal straining from different directions to get SH magnitude and orientation similar to the measured SH. The results showed that the modelled SH orientation at the different monitoring points could be achieved by applying different magnitudes of horizontal straining. These results suggested that the 0° Model with east-west directed maximum straining shows SH trends consistent with the measured SH trends. The east-west directed far-field horizontal stress derived during this study is consistent with the local movement direction of the Main Boundary Thrust (MBT) fault in the study area. The study revealed that the SH orientation is a better candidate for constraining the far-field horizonal stresses. Moreover, the study revealed that the local variation in the strike of MBT causes local variations in the orientation of far-field horizontal stresses in the HKS.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Ali, Wahid
author_facet	Ali, Wahid
author_sort	Ali, Wahid
title	Constraining the far-field maximum horizontal stress in the plate tectonic area
title_short	Constraining the far-field maximum horizontal stress in the plate tectonic area
title_full	Constraining the far-field maximum horizontal stress in the plate tectonic area
title_fullStr	Constraining the far-field maximum horizontal stress in the plate tectonic area
title_full_unstemmed	Constraining the far-field maximum horizontal stress in the plate tectonic area
title_sort	constraining the far-field maximum horizontal stress in the plate tectonic area
granting_institution	Universiti Teknologi Malaysia
granting_department	Faculty of Engineering - School of Civil Engineering
publishDate	2022
url	http://eprints.utm.my/102862/1/WahidAliPSKA2022.pdf.pdf
_version_	1783729226821664768

Constraining the far-field maximum horizontal stress in the plate tectonic area

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