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.

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A method of underwater wireless communications using visible-light radiation is proposed for high-speed data transmission and recovery in deep-sea environment. Acoustic communication technology is effective and has been used for underwater data transmissions because the underwater propagation distance of acoustic wave is farther than in the air. But its data transmission rate is lower, and its propagation direction maybe are refracted and changed by the nonuniformity of acoustic-speed distribution when the temperature changes of seawater, causing the unstable communication. On the other hand, visible-light wave with wavelength of 380 nm-780 nm is an excellent medium for application in underwater wireless communications, which has received much attention. Its attractive features are very low energy decay rate in seawater, easily control the propagation direction and position range by the visibility, and potential high data rate and capacity. However, visible-light waves in the seawater have the spectral attenuation characteristics due to different marine environment. So in this paper, an automatic-control method of data transmission with wavelength-adaptation function is considered for different seawater turbidity.

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Ocean bottom seismometer records seismograms using a clock in a recorder. The recorder has a very precise clock although a few seconds of time shift occurs during a one-year seafloor observation. Usually, we measure time difference between a recorder's clock and a GPS clock before and after an observation and calibrate recordings. Recently, we could not apply this method because of some trouble in a recorder. In this report, we show that we can estimate a time drift of recorder's clock using observed seismograms and calibrate recordings. One easy method to estimate a time drift is to measure a temporal change of differential travel time residuals of first P-wave between two stations. Other method is to measure a temporal change of ambient noise cross correlation function of two stations. In our recent seafloor observation by “Normal Oceanic Mantle project”, we had two troubled recorders of broadband ocean bottom seismometers (NM02, NM20). We have applied these methods and estimated time drifts of these two recorder's clocks as－10.49 ms/day, and －1.9 ms/day, respectively. We have also found that clock stability of these recorder's clocks is very well during seafloor observation from recordings by temporal change of cross correlation function and that a precision of the recorder's clock is well less than 100ms.

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The 1983 Nihonkai-Chubu earthquake (M7.7), 1993 Hokkaido Nansei-oki earthquake (M7.8) and other large earthquakes over M7, triggered by reverse fault mechanisms, have occurred along the eastern margin of the Japan Sea. However, the relationship between this earthquake and the crustal structure is not very clear, because the amount of seismic exploration data is very limited. From 2009 to 2012, we conducted the research of marine seismic surveys using a multichannel seismic system (MCS) and the ocean-bottom seismographs (OBSs) with the research vessels of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). This research was collaborated with “Multidisciplinary research project for construction of fault model in the high strain rate zone” of the Ministry of Education, Culture, Sports, Science, and Technology of Japan. In this research, seismic data using MCS were acquired along 43 lines in the region covered from the coast of the Japan Sea to the Yamato Basin and the Japan Basin. In this report, we describe data acquisition and the result of data processing on MCS survey.

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Recently, the demand of exploration of deep sea increases. The realization of a simple, a portable and a low-cost deep sea exploration system is also required. The purpose of the project ``Edokko No.1'' is to realize such a simple, a portable and a low-cost deep sea exploration video system. The project members are the CEO of the small companies in Tokyo downtown districts, universities, a research institute, a bank and volunteers of an electric company. The free-fall deep sea exploration video system, we call ``Edokko No.1'' recorded 3 D video of deep sea creatures at 7800\,m of the depth, successfully. The authors, who are the member of the Edokko No.1 project, installed temperature and atmospheric pressure sensors in glass spheres. In this paper, it is investigated that the sensors in the glass sphere is applicable in order to measure the temperature profile of the deep sea and is to detect the moment of the arrival at the bottom or of the departure from the bottom. As a result, it is confirmed that the volume deviation of the glass sphere calculated by the sensor outputs indicates the arrival at the bottom or the departure from the bottom of the free-fall system.

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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.

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