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dc.contributor.authorTong, Pingen_US
dc.identifier.citationTong, P. (2021). Adjoint-state traveltime tomography : eikonal equation-based methods and application to the Anza area in southern California. Journal of Geophysical Research: Solid Earth, 126(5), e2021JB021818-.
dc.description.abstractRay tracing is avoidable in seismic traveltime tomography. In this study, seismic traveltime tomography is reformulated as an eikonal equation-constrained optimization problem solved by the ray-free adjoint-state method. The resultant approach is called adjoint-state traveltime tomography. For completeness, an eikonal equation-based earthquake location method is developed to locate the hypocenters of earthquakes when necessary. The multiple-grid model parameterization is adopted to discretize the relative slowness perturbation urn:x-wiley:21699313:media:jgrb54900:jgrb54900-math-0001. The step-size-controlled gradient descent method, which has an effect of damping regularization, is used to find optimal earthquake hypocenters and velocity models. The performances of the earthquake location and adjoint-state traveltime tomography methods are tested in the source area of the 2020 Mw 4.9 Anza earthquake, a seismologically active place in southern California. The obtained high-resolution P-wave velocity model demonstrates that the 2020 Mw 4.9 Anza earthquake and other historic moderate-sized Anza earthquakes occurred near or at the boundaries of low VP rocks, a typical seismogenic environment for moderate to large crustal earthquakes. Meanwhile, the source zone of the Anza earthquakes is characterized by high VP/VS, indicating the possible existence of crustal fluids as well as the critical role of fluids in the occurrence of those moderated-sized Anza earthquakes. On the whole, the well-performed eikonal equation-based earthquake location method and adjoint-state traveltime tomography method provide competent and attractive tools for hypocenter and tomographic inversions.en_US
dc.description.sponsorshipMinistry of Education (MOE)en_US
dc.description.sponsorshipNanyang Technological Universityen_US
dc.description.sponsorshipNational Research Foundation (NRF)en_US
dc.relation.ispartofJournal of Geophysical Research: Solid Earthen_US
dc.rights© 2021 American Geophysical Union (AGU). All rights reserved. This paper was published in Journal of Geophysical Research: Solid Earth and is made available with permission of American Geophysical Union (AGU).en_US
dc.titleAdjoint-state traveltime tomography : eikonal equation-based methods and application to the Anza area in southern Californiaen_US
dc.typeJournal Articleen
dc.contributor.schoolSchool of Physical and Mathematical Sciencesen_US
dc.contributor.schoolAsian School of the Environmenten_US
dc.contributor.researchEarth Observatory of Singaporeen_US
dc.description.versionPublished versionen_US
dc.subject.keywordsSeismic Tomographyen_US
dc.subject.keywordsCrustal Structureen_US
dc.description.acknowledgementThis work is partly funded by Singapore MOE AcRF Tier-2 Grant (04MNP002073C230) and Singapore MOE AcRF Tier-1 Grant (04MNP000559C230). This work comprises Earth Observatory of Singapore contribution no. 276. 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).en_US
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