Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield

Seismic anisotropy provides crucial information on the stress state and geodynamic processes inside the Earth. We develop a novel adjoint-state traveltime tomography method using P-wave traveltime data to simultaneously determine velocity heterogeneity and azimuthal anisotropy of the subsurface. Fir...

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Main Author: Tong, Ping
Other Authors: School of Physical and Mathematical Sciences
Format: Article
Language:English
Published: 2021
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Online Access:https://hdl.handle.net/10356/153558
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Institution: Nanyang Technological University
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spelling sg-ntu-dr.10356-1535582022-01-01T20:11:19Z Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield Tong, Ping School of Physical and Mathematical Sciences Asian School of the Environment Earth Observatory of Singapore Science::Mathematics San-Andreas Fault Seismic Anisotropy Seismic anisotropy provides crucial information on the stress state and geodynamic processes inside the Earth. We develop a novel adjoint-state traveltime tomography method using P-wave traveltime data to simultaneously determine velocity heterogeneity and azimuthal anisotropy of the subsurface. First, an anisotropic eikonal equation is derived to model first-arrival traveltimes in azimuthally anisotropic media. Traveltime tomography is then formulated as an optimization problem constrained by the anisotropic eikonal equation, which is subsequently solved by the adjoint-state method. Ray tracing is not required. Its high accuracy is achieved by solving the anisotropic eikonal equation and the associated adjoint equation with efficient numerical solvers. In addition, an eikonal equation-based earthquake location method for azimuthally anisotropic media is developed to solve the coupled hypocenter-velocity problem. The tomography and earthquake location methods are applied to central California near Parkfield to test their performance in practice. A total of 1,068,850 first P-wave traveltimes clearly maps the velocity heterogeneity and azimuthal anisotropy in the upper and middle crust. The average P-wave velocity model shows a striking velocity contrast across the San Andreas Fault (SAF). In the upper crust, we find structural anisotropy in the SAF zone and stress-induced anisotropy off the SAF zone. In the middle crust, the fast P-wave velocity directions are generally fault-parallel due to the decreased effect of the maximum horizontal compressive stress. In all, the real-data application suggests that the new adjoint-state traveltime tomography method can be reliably used to investigate anisotropic seismic structures. Ministry of Education (MOE) National Research Foundation (NRF) Published version This work is supported by the Minister of Education, Singapore, under its MOE AcRF Tier-2 Grant (04MNP002073C230). This work comprises Earth Observatory of Singa-pore contribution no. 367. This research is also partly supported by the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centers of Excellence Initiative (Project Code Number: 04MNS001953A620). 2021-12-07T02:20:10Z 2021-12-07T02:20:10Z 2021 Journal Article Tong, P. (2021). Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield. Journal of Geophysical Research: Solid Earth, 126(10), e2021JB022365-. https://dx.doi.org/10.1029/2021JB022365 2169-9313 https://hdl.handle.net/10356/153558 10.1029/2021JB022365 2-s2.0-85118237203 10 126 e2021JB022365 en 04MNP002073C230 04MNS001953A620 Journal of Geophysical Research: Solid Earth © 2021 American Geophysical Union. All rights reserved. This paper was published in Journal of Geophysical Research: Solid Earth and is made available with permission of American Geophysical Union. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Science::Mathematics
San-Andreas Fault
Seismic Anisotropy
spellingShingle Science::Mathematics
San-Andreas Fault
Seismic Anisotropy
Tong, Ping
Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield
description Seismic anisotropy provides crucial information on the stress state and geodynamic processes inside the Earth. We develop a novel adjoint-state traveltime tomography method using P-wave traveltime data to simultaneously determine velocity heterogeneity and azimuthal anisotropy of the subsurface. First, an anisotropic eikonal equation is derived to model first-arrival traveltimes in azimuthally anisotropic media. Traveltime tomography is then formulated as an optimization problem constrained by the anisotropic eikonal equation, which is subsequently solved by the adjoint-state method. Ray tracing is not required. Its high accuracy is achieved by solving the anisotropic eikonal equation and the associated adjoint equation with efficient numerical solvers. In addition, an eikonal equation-based earthquake location method for azimuthally anisotropic media is developed to solve the coupled hypocenter-velocity problem. The tomography and earthquake location methods are applied to central California near Parkfield to test their performance in practice. A total of 1,068,850 first P-wave traveltimes clearly maps the velocity heterogeneity and azimuthal anisotropy in the upper and middle crust. The average P-wave velocity model shows a striking velocity contrast across the San Andreas Fault (SAF). In the upper crust, we find structural anisotropy in the SAF zone and stress-induced anisotropy off the SAF zone. In the middle crust, the fast P-wave velocity directions are generally fault-parallel due to the decreased effect of the maximum horizontal compressive stress. In all, the real-data application suggests that the new adjoint-state traveltime tomography method can be reliably used to investigate anisotropic seismic structures.
author2 School of Physical and Mathematical Sciences
author_facet School of Physical and Mathematical Sciences
Tong, Ping
format Article
author Tong, Ping
author_sort Tong, Ping
title Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield
title_short Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield
title_full Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield
title_fullStr Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield
title_full_unstemmed Adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central California near Parkfield
title_sort adjoint-state traveltime tomography for azimuthally anisotropic media and insight into the crustal structure of central california near parkfield
publishDate 2021
url https://hdl.handle.net/10356/153558
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