The effects of the complex seismic structure in the lowermost mantle on the seismic SmKS phases that propagate beneath the core-mantle boundary are important, but as yet unclear. Thus, in this study, broadband waveform modeling with the spectral element method is conducted using the Earth Simulator. One-hour length seismograms are first synthesized with one-dimesional velocity structure of PREM, and the portions of the SmKS phases are retrieved. The shortest period that the Earth Simulator can achieve is up to 3.5 s, which is too long to reproduce S5KS and higher SmKS phases. To read the differential travel times of SmKS phases accurately, the phase-weighted stack is adopted and the uncertainty is inferred with the bootstrap method. Next, wave fields are simulated with three-dimensional velocity structures of S20RTS with emphasized velocity perturbation at the base of the mantle and SB4L18 expanded by spherical harmonics. The Earth Simulator enables the generation of a three-dimensional (3D) structure using spherical harmonics coefficients of up to 40 degrees. The different models result in different residuals for differential travel times of S4KS-S3KS and S3KS-S2KS and change in the incident azimuths of S3KS with respect to S2KS, even if global tomography models with long-wavelength heterogeneity of several thousand kilometers are used. These results clearly suggest that there are strong effects of heterogeneity in the lowermost mantle on the differential travel times of S4KS-S3KS and S3KS-S2KS. The characteristcs of the uncertainty depend on the 3D-mantle models, which may provide clues to the separation of the effects of heterogeneity at the base of the mantle for SmKS anomalies.
In order to extract quantitative information on deep-sea benthic animals (no. individuals or biomass in an area) using oblique video/photo images taken by deep-sea submersible survey platforms, a new method was established to estimate the imaged area of the seafloor from the oblique images. The trapezoidal area appearing on the lower half of the screen was calculated using underwater horizontal and vertical aperture angles of the camera, the angle of incidence of the camera, and the camera-to-seafloor distance. The incidence angle of the camera was obtained using the angles of vehicle pitch and camera tilt, while the camera-to-seafloor distance was calculated from the lens-to-vehicle bottom distance, horizontal distance of lens-to-altimeter, and vehicle altitude. The areas estimated by the present method from images taken by some submersible survey platforms were comparable to those that were actually measured. With the above parameters, and by focusing on the lower half of an image, our method can be used for estimating the seafloor area from any oblique video/photo images taken by any submersible survey platform. Thus, this method is useful for the extraction of quantitative data on benthic animals from legacy oblique video/photographs acquired by submersible survey platforms.