Tomoki Watanabe

Delamination structure imaged in the source area of the 1982 Urakawa-oki earthquake

[1] The Kuril arc collides with the northeast Japan arc in the southern part of Hokkaido, Japan. 3-D tomographic inversion of data from a dense network of sensitive ocean-bottom seismographs and land stations has allowed imaging of previously unseen details of the arc-arc collision structure. A low velocity body dips gently southwestward, at depths of 35 to 45 km, from east of the Hidaka Mountains to the source area of the 1982 Urakawa-oki destructive earthquake (Ms 6.8). The low velocity body is the lower half of the lower crust of the Kuril arc, which must have been delaminated by the collision. We believe that the continuing collision of the delaminated lower crust with the northeast Japan arc resulted as an episode of aseismic slow slip prior to the 1982 Urakawa-oki earthquake as well being the reason for the high seismic activity in this region.

A soccer field tracking method with wire frame model from TV images

This paper proposes a tracking method of soccer field area in a soccer video captured from TV. The camera taking the soccer game video is controlled by three parameters: its mount position, the angle, and the magnification. In order to estimate these three parameters, the proposed method designs a wire frame model, which represents the official layout of the soccer field lines; and by the wire frame model matching with the field area in the video, the above three parameters can be estimated, even if the soccer video includes the camera panning, zooming, etc. By using the estimated parameters, we can accurately obtain where the field area corresponds in the actual soccer field. Some experiments in tracking the field area in actual soccer videos are performed and their results verify the high performance of the proposed method.

Scientific results from underwater earthquake monitoring using cabled observatories

Scientific results started appearing in the literature using realtime and continuous time series of data obtained on the seafloor for seismic and micro-tsunamic observations. JAMSTEC has developed three out of a total of eight cabled observatories in the Japanese water. The installed observatories are all operating to aid earthquake studies for disaster mitigation at the future potential hazards, which take place at plate boundaries surrounding the Japanese islands. Along with earthquake activity monitoring purposes, it has become clear that there are potentially and scientifically meaningful outcome from such observations. We summarize the latest scientific results from monitored data produced by our cabled observatories and, then, to demonstrate advantages of such underwater seismic and tsunamic stations. Until now, three main areas could be pointed out as meaningful scientific products from cabled observations: (1) fine mapping of offshore seismicity, (2) modeling of micro-tsunamic pressure fluctuations caused by deep earthquakes, and (3) constraining earthquake source parameters such as source depths of offshore events using tsunami simulation. They are all interesting scientific results from the observational data could also readily be exploited for earthquake studies on deformation processes at the plate boundaries and on early tsunami warning system as a part of future disaster mitigation methodologies. It is obvious that newly deployed monitoring systems have revealed, at least partially, meaningful phenomena, which have been invincible due to lack of observations in the offshore. Technical and theoretical developments for offshore earthquake monitoring must be well considered for profound perception of geophysical processes associated with offshore seismic activities.

Aftershock observation of the 2003 Tokachi-oki earthquake by using dense ocean bottom seismometer network

The Tokachi-Oki earthquake occurred on September 26, 2003. Precise aftershock distribution is important to understand the mechanism of this earthquake generation. To study the aftershock activity, we deployed forty-seven ocean bottom seismometers (OBSs) and two ocean bottom pressure meters (OBPs) at thirty-eight sites in the source region. We started the OBS observation four days after the mainshock for an observation period of approximately two months. In the middle of the observation period, nine OBSs near the epicenter of the mainshock were recovered to clarify the depth distribution of aftershocks near the mainshock. From the data overall OBS, seventy-four aftershocks were located with high spatial resolution. Most of the aftershocks were located in a depth range of 15–20 km and occurred within the subducting oceanic crust, the 5.5-km/s layer of the landward plate and the plate boundary. No aftershocks were found in the mantle of the subducting plate. The low seismic activity beneath the trench area where the water depth is greater than about 2000 m suggests a weak coupling between the two plates. The depth of the mainshock is inferred to be 15–20 km from the aftershock distribution.

Trial of Multidisciplinary Observation at an Expandable Sub-Marine Cabled Station “Off-Hatsushima Island Observatory” in Sagami Bay, Japan

Sagami Bay is an active tectonic area in Japan. In 1993, a real-time deep sea floor observatory was deployed at 1,175 m depth about 7 km off Hatsushima Island, Sagami Bay to monitor seismic activities and other geophysical phenomena. Video cameras monitored biological activities associated with tectonic activities. The observation system was renovated completely in 2000. An ocean bottom electromagnetic meter (OBEM), an ocean bottom differential pressure gauge (DPG) system, and an ocean bottom gravity meter (OBG) were installed January 2005; operations began in February of that year. An earthquake (M5.4) in April 2006, generated a submarine landslide that reached the Hatsushima Observatory, moving some sensors. The video camera took movies of mudflows; OBEM and other sensors detected distinctive changes occurring with the mudflow. Although the DPG and OBG were recovered in January 2008, the OBEM continues to obtain data.

Double seismic zone in the Hokkaido Island, Southern Kurile arc, derived from off-Kushiro permanent OBS and land-based observations

We located hypocenters for more than two years, using combined datasets from land-based observations and ocean-bottom seismological data acquired by a permanent cable geophysical observatory system (JAMSTEC system), installed off Kushiro-Tokachi in July 1999. Hypocenter distribution characterizes that: 1) double seismic zone just east of the cabled observatory system, 2) a relatively low seismicity west of the cabled system, and 3) characteristic shallow seismic activity below the cabled system.

Reaction of quadricyclane with electron deficient p-benzoquinones

Quadricyclane reacted thermally in a [π2+σ2+σ2] manner with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and chloranil to give cyclobutanes and a spiro oxetane, respectively

Seismological monitoring on the 2003 Tokachi-oki earthquake derived from permanent OBSs and land-based observation - a challenge in monitoring M8 earthquake on the ocean floor

In July 1999, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) installed a cabled geophysical observatory system off Kushiro, southeastern Hokkaido Island, Japan. This observatory system comprises three ocean bottom seismographs (OBSs), two tsunami gauges, and a cable-end environmental monitoring system, connected with a 240 km long fiber optical cable. Processing OBSs and land-based data together, and comparing magnitude common recorded with that determined by Japan Meteorological Agency (JMA), we found event detection level was improved down to magnitude 1.5, which is much lower than the previously designed as down to magnitude around 2. We compared detection level before and after installing OBSs, and found dramatic improvement on the earthquake detection level after installation of the cabled system. Four years and two months after the installation, a megathrust earthquake (The 2003 Tokachi-oki earthquake, MJMA 8.0) occurred just beneath the system. The system recorded clear unsaturated seismograms just at 28.6 km from the epicenter, which is the first observation on the ocean floor recording an earthquake with magnitude eight in the world. This paper reports hypocenter distribution derived from permanent cabled OBSs and land-based observation in the period from mainshock of the 2003 Tokachi-oki earthquake, to middle of May 2004. In the large slip area of the mainshock, a planar, with ten-degree dip, hypocenter distribution is obtained. Another deep planar seismic zone is found about 20 km depth from the plate interface. We think that the geophysical observations helps to understand the initiation process of the rupture of the 2003 Tokachi-oki earthquake and that observations including seismological, geodynamic, hydrogeological, and the other multidisciplinary observations would provide a clue to future understanding of seismogenic processes at southern end of the Kurile subduction zones

Long-term seafloor and land-based sesismological monitoring at southwestern end of the Kurile subduction zone, based on more than six-year continuous observation

Around Japanese islands, most of subduction-related megathrust earthquakes occur offshore seismogenic zone, and are difficult targets in seismological and disaster mitigation studies. In June 1999, JAMSTEC installed a seismological/geophysical cabled observatory with length of approximately 240 km, off Kushiro-Tokachi, southeastern off Hokkaido, Japan. The system locates near southwestern end of the Kurile subduction zone, where megathrust earthquakes are taking place repeatedly. For in-situ seismological/geophysical monitoring at plate boundary, which is one of the leading hopes to investigate the subduction process and related phenomena in detail, we reviewed more than six-year automatic event-based seismological data since September 2000, when a continuous recording and related automatic event detection against cabled seismological data combined with land-based observation started. Above long-term observation includes onset of a megathrust earthquake (2003 Tokachi-oki earthquake, M8.0) just beneath our cabled system and the following intense aftershock activity, which we first experienced on the ocean floor. In this paper, we summarize several remarks based on the results, including experiences with our observation.

Seismic/Geodetic Permanent Monitoring Using Submarine Cables

Scientific results started appearing in the literature using realtime and continuous time series of data obtained on the seafloor for seismic and micro-tsunamic observations. The installed observatories are all operating to aid earthquake studies for disaster mitigation at the future potential hazards which take place at plate boundaries surrounding the Japanese islands. We summarize the latest scientific results from monitored data produced by our cabled observatories and, then, to demonstrate advantages of such underwater seismic and tsunamic stations. The development of offshore monitoring system must be well considered for profound perception of geophysical processes associated with offshore seismic activities.