Seismic Velocity Structure Beneath the Tofino Forearc Basin Using Full Waveform Inversion
Date
2021
Authors
Yelisetti, Subbarao
Spence, George D.
Journal Title
Journal ISSN
Volume Title
Publisher
Energies
Abstract
Given the effects of steep dips and large lateral variations in seismic velocity beneath the
Vancouver Island continental shelf, seismic processing and travel time inversion are inadequate
to obtain a detailed velocity model of the subsurface. Therefore, seismic full waveform inversion
is applied to multichannel seismic reflection data to obtain a high-resolution velocity model beneath
the Tofino fore-arc basin under the continental shelf off Vancouver Island margin. Seismic
velocities obtained in this study help in understanding the shallow shelf sediment structures, as
well as the deeper structures associated with accreted terranes, such as Pacific Rim and Crescent
terranes. Shallow high velocities, as large as ~5 km/s, were modeled in the mid-shelf region at ~1.5–2.0 km depth. These coincide with an anticlinal structure in the seismic data, and possibly
indicate the shallowest occurrence of the volcanic Crescent terrane. In general, seismic velocities
increase landward, indicating sediment over-consolidation related to the compressional regime
associated with the ongoing subduction of the Juan de Fuca plate and the emplacement of Pacific
Rim and Crescent accreted terranes. Seismic velocities show a sharp increase about 10 km west
of Vancouver Island, possibly indicating an underlying transition to the Pacific Rim terrane. A
prominent low velocity zone extending over 10 km is observed in the velocity model at 800–900 m
below the seafloor. This possibly indicates the presence of a high porosity layer associated with
lithology changes. Alternatively, this may indicate fluid over-pressure or over-pressured gas in this
potential hydrocarbon environment.
Description
Keywords
seismic velocity, full waveform inversion, Tofino basin, accreted terranes, low velocity zone
Citation
Yelisetti, S. & Spence, G. D. (2021). Seismic Velocity Structure Beneath the Tofino Forearc Basin Using Full Waveform Inversion. Energies, 14(11), 1-24. https://doi.org/10.3390/en14113099.