Overthickened Lithosphere Beneath the Blanco Transform Faults
The complex interaction between mid-ocean ridges and oceanic transform faults demands validation of the half-space cooling model for the thermal evolution of oceanic lithosphere at the ridge-transform systems. Seismic tomography is key for accurately deciphering the lithosphere structures in the transform faults. Thanks for the unprecedented opportunity provided by an ocean-bottom seismometer experiment at the Blanco Transform Faults (BTF) of the northeastern Pacific, here we present a three-dimensional seismic velocity tomographic model of the lithosphere and top asthenosphere beneath this fault system. We carried out data pre-processing of the OBS data by removing the tilt and compliance noises for the vertical-component waveforms, correcting for the clock drift via an improved noise cross-correlation function method, verifying the polarity of the vertical component and determining the horizontal orientations via a phase-tracking method. We then extracted dispersion measurements from teleseismic Rayleigh waves and the empirical Green’s functions retrieved from ambient noise, as well as the amplitude ratio between the radial and vertical components (H/V ratio) of Rayleigh waves. These measurements were applied to a jointly inversion of phase-velocities and H/V ratios for the S-wave velocity model via surface-wave tomography and a Bayesian Monte Carlo method. The most shocking finding in the model is that high velocities dominate the uppermost mantle of the eastern BTF. We attribute the velocity variation in the mantle primarily to temperature variation and establish new isotherms along the BTF. Unlike previous studies, our 600°C isotherm well correlates the depth extent of earthquake sources beneath the whole BTF. The lithosphere-asthenosphere boundary beneath the eastern BTF indicated by the model-predicted 1200°C isotherm is deeper than that derived from the half-space cooling model. Our results suggest the lithosphere had been thickened for millions of years prior to the formation of a mature oceanic transform system.
Session: Seismology in the Oceans: Pacific Hemisphere and Beyond - II
Type: Oral
Room: Tubughnenq’ 3
Date: 5/2/2024
Presentation Time: 10:30 AM (local time)
Presenting Author: Xueyang Bao
Student Presenter: No
Additional Authors
Xueyang Bao Presenting Author Corresponding Author baoxy@sustech.edu.cn Southern University of Science and Technology |
Andy Dai 12031279@mail.sustech.edu.cn Southern University of Science and Technology |
Yingjie Yang yangyj@sustech.edu.cn Southern University of Science and Technology |
Jiashun Hu hujs@sustech.edu.cn Southern University of Science and Technology |
Wei Zhang zhangwei@sustech.edu.cn Southern University of Science and Technology |
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Overthickened Lithosphere Beneath the Blanco Transform Faults
Category
Seismology in the Oceans: Pacific Hemisphere and Beyond
Description