Crustal structures near a linear oceanic ridge, the Gagua Ridge, between the West Philippine Basin and the Huatung Basin in the western Philippine Sea were imaged based on head-wave, refracted and reflected P-wave arrivals recorded from 24 oceanbottom seismometers (OBS). Velocity anomaly zones, one below the Gagua Ridge summit and the others beneath two toes of the Gagua Ridge, imaged by large lateral variations in P-wave velocity of 5.5 -6.4 km s -1 and low velocity of 4 -5 km s -1 in the upper crust may have been generated when the Gagua Ridge was formed. East of the ridge, velocity anomaly zones, constrained by large lateral variations in P-wave velocity (4.8 -6.4 km s -1 ), relatively low velocity (4 -5 km s -1 ) and laterally high anomaly of Poisson's ratio (0.02 -0.04) in the upper crust and abrupt crustal thickening (6 -8.5 km) northward were obtained. West of the ridge, the velocity anomaly zones indicated by large lateral variations in P-wave velocity (5.2 -6.2 km s -1 ) and laterally high anomaly of Poisson's ratio (0.02 -0.04) in the upper crust and thick crust (thickening southward from 9 -12 km) were found below the Huatung Basin and the Western Trough of the Gagua Ridge. Abrupt crustal thickening northward east of the ridge may be related to northwestward convergence of the Philippine Sea Plate. These velocity anomaly zones in the upper crust at both sides of the ridge might result from deformed, fractured or faulted zones. These zones support E -W compression, N -S shearing (or transpression) and uplifting that may have also created the Gagua Ridge and crustal thickening west of the ridge.
ABSTRACT1 Institute of Applied Geosciences, National Taiwan Ocean University, Keelung, Taiwan, ROC * Corresponding author address: Prof. Tan K. Wang, Institute of Applied Geosciences, National Taiwan Ocean University, Keelung, Taiwan, ROC; E-mail: tkwang@mail.ntou.edu.twImaging of 3D structural interfaces through reflected rays shooting from common-shot gathers is presented in this paper. First, by fitting the reflected arrivals picked from common-shot gathers, we calculate apparent dips and the shortest distances between sources and reflectors along two profiles. Then, based on the geometry of the profiles and a planar reflector, a unit normal vector of the reflector is determined from the apparent dips and the azimuths of two oblique profiles. A special case, when apparent dips are zero along two parallel profiles, for determining the reflector normal is also investigated. We propose three criteria to ensure the selected travel-times along two profiles resulting from the same planar reflector. These are that firstly, the same shortest distance from sources to the reflector is utilized; and secondly, we want to ensure the same normal of the reflector, and finally, the same ray distance.Prestack inverse-rays developed in this paper are applied to image the bathymetry of the Hoping Basin in the southernmost Ryukyu subduction zone and the fourth layer of the SEG/EAEG over-thrust model. Based on common-shot gathers along seven oblique profiles in the Hoping Basin, most of the reflection points are well imaged through inverse rays except when variation of the interface depth exceeds 300 m across profiles with spacing greater than about 20 km. Inverse-ray imaging of the over-thrust model also provides good agreement to its fourth interface except that imaging errors of about 1 km in depth are found near the thrust faults.Inverse-ray imaging of 3D structures from 2D multi-channel seismic profiles is demonstrated if a pseudo-3D structure (a planar reflector) exists TAO, Vol. 16, No. 3, August 2005 548 between profiles or if at least two profiles are within a Fresnel zone. Although this technique deals with a single-layered problem currently, it is fundamentally important when we extend it to image inhomogeneous multilayered media.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.