Tohoku Earthquake Tsunami Research Articles

Tsunami-induced magnetic fields detected at Chichijima Island before the arrival of the 2011 Tohoku earthquake tsunami

Magnetic field disturbances associated with the tsunami caused by the 2011 Tohoku earthquake were observed at Chichijima Island, 1200 km south of the epicenter. The vertical component of the magnetic field showed a periodic signal at approximately 20 min before the tsunami arrived. This study investigated the mechanism of the magnetic field signal using simulation studies. First, we derived a tsunami source model that explained the tide gauge records and sea-level changes at Chichijima Island. Using this model, we then computed the electric current induced by the tsunami and the resulting secondary magnetic field. The computed changes in sea level and magnetic field are consistent with their respective observed waveforms, including the timing of the magnetic field signals. In our interpretation, the tsunami flow induced an electric current along the tsunami wave front, which in turn generated a secondary induced magnetic field ahead of the tsunami wave. Hence, magnetic variations preceding the tsunami were observed at Chichijima Island. This suggests that imminent arrivals of tsunamis can be detected by observations of the magnetic field.

Erratum: "Survey on Railway Operator Actions and Preparedness in Transportation Against 2010 Chile Earthquake Tsunami and 2011 Tohoku Earthquake Tsunami"

The preparedness and the emergency management against tsunami are an increasingly important issue for public transportation operators. The current state of these two is studied by conducting the hearing and questionnaire survey for domestic operators, in addition to the hearing by the national and local governments, focusing on actual actions taken against the 2010 Chile Earthquake Tsunami and the 2011 Tohoku Earthquake Tsunami. Critical issues are discussed in order to promote the preparedness against Tokai–Tonankai–Nankai Earthquake Tsunami which is likely to occur in the near future.

Assessment of the Effectiveness of General Breakwaters in Reducing Tsunami Inundation in Ishinomaki

The 2011 Great East Japan Earthquake and Tsunami caused devastation all along the coast of eastern Japan. Ishinomaki City was one of the most severely damaged municipalities, though the height of the tsunami in this city was smaller than that in Iwate and northern Miyagi. A large difference in the extent of building damage was found comparing two areas of Ishinomaki: one not protected by breakwaters, and the other behind the breakwaters of a large Fishery port. In this paper, the authors perform numerical simulations to determine whether these general breakwaters, which were designed not to block tsunamis but wind waves, reduced the tsunami's energy and contributed to a reduction in inundation of the areas behind the port. Before assessing the effectiveness of breakwaters against tsunamis, simulated inundation heights in each of these two areas were compared with heights measured by The 2011 Tohoku Earthquake Tsunami Joint Survey Group. It was found that a simulation with larger Manning's n value (n = 0.30) can evaluate inundation more precisely than when this value is small (n = 0.06), as often used by Japanese coastal engineers. Comparing the region protected by breakwaters with the unsheltered area, the results of a 2D shallow water equation model do not show a significant difference in inundation mainly because the tsunami intrudes through the openings in the breakwater and fills up the port basin with seawater in a very short time. Therefore, the effectiveness of general breakwaters in reducing tsunami impact should not be overestimated. However, a hypothetical study shows that water levels could be greatly reduced if the port were fully enclosed by breakwaters. This implies that a port could substantially reduce tsunami inundation if the breakwater openings were equipped to be closed before tsunami arrival. The authors also demonstrate that the difference in the extent of building damage in the two areas of Ishinomaki considered can be explained by the difference in drag forces due to the topography as well as the difference in land use, rather than by the presence of breakwaters.

OPTIMUM SCHEME OF ADAPTIVE MESH REFINEMENT FOR TSUNAMI SIMULATION

A long wave model with nesting scheme is widely used for tsunami simulation and impact assessment, generally. The conventional nesting scheme, however, has disadvantages for analyzing larger computational mesh size along the coast and needs expensive computation costs. Adaptive Mesh Refinement (AMR) method can consider the interactions of different grids and reduce computational cost together. This study applied the AMR for calculation of long wave propagations, and the different mesh refinement schemes were applied and optimized by a series of numerical experiments. The model was applied to the 2011 Tohoku Earthquake Tsunami, and the model was validated against the post tsunami inundation survey data.

FIELD INVESTIGATION OF LONG-TERM MOORING CHAIN SYSTEM DURABILITY OF THE GPS TSUNAMI-WAVE METER

This paper aims for providing basic information of the mooring design of the GPS mounted Tsunami-Wave meter buoy, which successfully observed exact offshore tsunami profile of the 2011 off the Pacific coast of Tohoku Earthquake. Deep-sea sensors can detect tsunami profiles minutes before its arrival on the coast. That is very important to prevent and/or reduce tsunami disasters (Nagai, et.al., 2006). But as tsunamis are very rare events for human life scale, it is difficult for human societies to keep the offshore tsunami monitoring system in good condition for long years, if the system is applicable only for tsunami detection. Real-time offshore tsunami detection system should be well maintained only if the system provides us routine useful sea information like waves and swells. Routine multi-purpose usefulness of the observed data may make the system more cost effective than only be applicable for very rare and immediate tsunami monitoring (Nagai, et.al., 2007). Existing deep-sea seabed installed pressure gauge is applicable only to tsunami event, for deep-sea wave and swell actions do not reach the seabed. That is why offshore GPS buoy system is the only one technique that has succeeded to serve authorized real-time tsunami warning before its arrival to the coast line at the 2011 off the Pacific coast of Tohoku Earthquake tsunami event in Japan. In this paper, authors introduce observation data of proto-type GPS buoy's mooring chain at 3 years and 7 months after the installation in the severe sea condition, in order to provide information for practical design of future safer and more economical design of the mooring system.

Inundation behavior of the 2011 Tohoku earthquake tsunami in the Taro District, Miyako City, northeast Japan, as inferred from directional traces

The tsunami caused by the 2011 Tohoku earthquake devastated numerous cities, towns, and villages in coastal areas of Japan. The tsunami also left varied and numerous traces in onshore areas, which provide insights into the nature of tsunami inundation patterns and methods for mitigation of feature tsunami disasters. This paper focuses on tsunami traces that provide information on flow directions, such as groove marks on concrete and asphalt surfaces, and bent poles. Based on the distribution of directional traces, the flow patterns of the tsunami were estimated in the inundation area of the Taro District, Miyako City, northeast Japan. The inundation behavior is generally consistent with the hypothesis of run-up and backwash pattern suggested by previous investigations (run-up flows tend to be perpendicular to coastlines, whereas backwash flows tend to favor topographic lows). Examination of the relationship between the inundation behavior and the barriers constructed in Taro District shows that the barriers would slightly influence inundation behavior and implies that they may not be effective for reducing entire damage when tsunamis overflow barriers. Regional difference of the inundation behavior relates areal difference between the most destructed area and other areas. The difference of intensity of damages would be caused by that of land use in coastal areas.

The impact of the 2011 Tohoku earthquake tsunami disaster and implications to the reconstruction

The authors conducted a comprehensive study to identify the impact of the 2011 Tohoku tsunami disaster and to understand the lessons towards the reconstruction of Tohoku to build tsunami-resilient community. First, the authors identified the extent of tsunami inundation zone by field measurement and satellite remote sensing. A specific index for optical satellite images was applied for the extraction of tsunami inland penetration calibrated with the ground truth data (field survey data). Second, an integrated investigation of field measurement and aerial photo and video inspections with spatial information sciences was performed to understand the hydrodynamic aspect of tsunami inland penetration with a form of tsunami flow velocity and hydrodynamic force, and the preliminary results lead to new understandings of structural vulnerability against the 2011 tsunami with a form of tsunami fragility curve and an implication for land use management and relocation planning to reconstruct resilient coastal communities.

Survey on Railway Operator Actions and Preparedness in Transportation Against 2010 Chile Earthquake Tsunami and 2011 Tohoku Earthquake Tsunami

The preparedness and the emergency management against tsunami are an increasingly important issue for public transportation operators. The current state of these two is studied by conducting the hearing and questionnaire survey for domestic operators, in addition to the hearing by the national and local governments, focusing on actual actions taken against the 2010 Chile Earthquake Tsunami and the 2011 Tohoku Earthquake Tsunami. Critical issues are discussed in order to promote the preparedness against Tokai–Tonankai–Nankai Earthquake Tsunami which is likely to occur in the near future.

Ecological impacts of the 2011 Tohoku Earthquake Tsunami on aquatic animals in rice paddies

The 2011 Tohoku Earthquake Tsunami hit the Pacific coast of eastern Japan on March 11, 2011 and disturbed various ecosystems, including rice paddies along the coast. In Miyagi Prefecture, located in the Tohoku Region, a total of 12685 ha, or about 11.5 % of the rice paddies, were inundated and damaged by the tsunami. Although rice paddies are artificially constructed, they have long been used by many kinds of aquatic animals as habitats. To assess impacts of the 2011 Tohoku Earthquake Tsunami on aquatic animals inhabiting the rice paddies, census surveys were conducted at inundated and non-inundated rice paddies at six sites along the coast of Miyagi Prefecture from June to July 2012. This was 30–60 days after the first transplanting of rice seedling in inundated rice paddies following the tsunami. In the surveys a total of 100 aquatic animal taxa, 72 from inundated and 86 from non-inundated rice paddies, were found. Although the taxonomic richness and composition differed among the sites, the total number of observations of walk dispersers and obligatory aquatic animals without resting stages were significantly lower in inundated than in non-inundated rice paddies. However, no notable difference was detected in taxonomic richness and the total number of observations of flight dispersers and obligatory aquatic animals with resting stages between inundated and non-inundated rice paddies. The results showed that the tsunami had a substantial impact on freshwater animals but that restoration of the paddies for rice cultivation enhanced rapid recolonization by aquatic animals with high dispersal abilities and resting stages.

Geomorphic effects on the changes in landforms and vegetation caused by the 2011 Tohoku Earthquake Tsunami.

Geomorphic effects on the changes in landforms and vegetation caused by the 2011 Tohoku Earthquake Tsunami.

Abandonment of farmlands caused by the 2011 Tohoku Earthquake tsunami disaster and river flood disaster in the unprotected floodplain of the Lower Natori River, Japan

Abandonment of farmlands caused by the 2011 Tohoku Earthquake tsunami disaster and river flood disaster in the unprotected floodplain of the Lower Natori River, Japan

浮沈式大型津波シェルターに作用する流体力低減とその運動特性

After the Tohoku earthquake tsunami in Japan, many evacuating options from a huge tsunami, e.g. tsunami tower, large building, moving onto hill, stronger breakwater, underground shelter and small lifeboat, have been proposed in recent years. In this paper, the authors have proposed and developed one kind of a large-sized tsunami shelter with mooring that is capable of accommodating at least one hundred people or more to evacuate from a run-up tsunami. The optimization for the shape of the tsunami shelter was also examined using Particle method, Smoothed Particle Hydrodynamics. The tsunami force acting on the desired shape was compared with that on the basic shape, e.g. a rectangular shape. The proposed tsunami shelter could be one of useful options for evacuating from a huge tsunami attacking near coastal area.

Coastal forest damage and tide prevention function following the 2011 Tohoku Earthquake Tsunami : North Sanriku coast area

Coastal forest damage and tide prevention function following the 2011 Tohoku Earthquake Tsunami : North Sanriku coast area

合成開口レーダー画像による津波浸水ラインの半自動抽出ツールの開発

A semi-automated tool for detecting tsunami flooded areas is developed using high-resolution Synthetic Aperture Radar data (TerraSAR-X) focusing on the 2011 Tohoku earthquake tsunami event. A number of flood detection techniques proposed in previous studies have not been fully utilized for emergency responses due to their complicated procedures for image processing. Therefore,this study aimed at solving this problem by developing a semi-automated tool to detect flooded areas with a simple interface. The model was applied to Sendai plain and demonstrated a good performance showing producer's accuracy of 94.2 % and user's accuracy of 93.8 %.

東北地方太平洋沖地震動によるドルフィン振動に伴う係留船舶の動揺および係留索切断に関する一考察

Many sea disasters of vessels moored along the terminals occurred during the 2011 Tohoku Earthquake Tsunami. We conducted surveys of the sea disasters for two large crude oil carriers moored at dolphin terminals. The mooring lines breakages happened not only in the tsunami attack but also in the seismic vibrations. In this study, we have composed a time domain model to estimate the moored ship behavior due to oscillations of dolphins during earthquake, and investigated the Aframax tanker behavior moored at dolphins during the seismic vibration which was actually recorded at the harbor. It is clarified that there is a possibility to push out the tanker and induce the mooring line breakage due to oscillations of dolphins during earthquake.

南海トラフにおける多数津波シナリオの設定方法とその応用

In the 2011 Tohoku Earthquake Tsunami Disaster, the actual tsunami heights had exceeded the estimated heights extremely and the underestimation caused serious damages in Japan. To reduce such a risk, multi tsunami scenarios were examined especially considering Large Slip Zone (LSZ) and Super Large Slip Zone (SLSZ) suggested by the Cabinet Office, Government of Japan. And a recipe of predicting the scenarios is proposed in this paper. The recipe consists of areas, shapes, places and dislocations of LSZ and SLSZ, and the initial crack location. The recipe was applied for the Nankai Trough to predict multi scenario of future large tsunamis and its detailed procedure was shown. Further, the multi tsunami scenarios upgraded the model to avoid the underestimation of tsunami warning by using GPS-mounted Buoys.

Correction: Immediate Ecological Impacts of the 2011 Tohoku Earthquake Tsunami on Intertidal Flat Communities

An error was introduced in the preparation of this article for publication. In the Methods section, there is an error in the fourth equation of the Statistical Analyses section. There is a / missing between (b-c) and b. The correct equation is N=(b-c)/b x 100.

The Feature of Thunami Height Categorized by Coastal Landform, Comparison of Meiji Sanriku Tsunami with the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami, Japan

The Feature of Thunami Height Categorized by Coastal Landform, Comparison of Meiji Sanriku Tsunami with the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami, Japan

Lessons from the 2011 Tohoku Earthquake Tsunami Disaster

Based on a comprehensive study of the lessons from the 2011 Great East Japan earthquake and tsunami that devastatedmuch of the northeast Japan (Tohoku), we discuss insights into reconstruction and tsunamiresilient communities. Through field measurement, remote sensing, and numerical modeling approaches with spatial information sciences, we clarified the hydrodynamic characteristics of the tsunami inundation flow, the tsunami fragility curves. As observed in devastated areas and the analysis of the tsunami fragility curves, buildings were especially vulnerable when the local flow depth exceeded 2 m, while a 6 m flow depth would cause everything to be washed away. The findings and results lead to implications for land use management and relocation planning for reconstructing tsunami-resilient coastal communities. As a case study, we conducted the numerical tsunami modeling in Sendai city to evaluate the performance of the reconstruction plan based on the land use and coastal protection scenarios.

Railway Structure Damage to the East Japan Railway Company by the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami

The huge tsunami generated by a 9.0 Mw earthquake (off the Pacific Coast of Tohoku Earthquake) and centered off the coast of Sanriku, Tohoku, on March 11, 2011, damaged 7 lines of the East Japan Railway Company. Bridge girders were swept away, piers were broken or tipped, and embankments and station buildings were swept away. This paper reports typical examples of railway structure damage due to this tsunami.