Published papers

Since the 1995 Hanshin-Awaji earthquake disaster, damage estimation analyses for potential earthquake hazards have been carried out by many administrative organizations in Japan. One of the key issues in these analyses is to estimate the number and spatial distribution of human casualties as accurately as possible. We focused on Nishinomiya City, which was one of the most heavily damaged cities in the Hanshin-Awaji earthquake disaster, and constructed a built environment database of Nishinomiya City. Using this database, constructions of the age and sex of individuals and the spatial distribution of the dead, as well as the relationships between the ages of houses and ages of the dead were investigated. This paper provides a technique of constructing a relational geographic information system (GIS) database with several different types of data. Using this GIS database and through Weibull analysis, we arrived at two conclusions regarding the distribution of the age and sex of the dead caused by the earthquake. (1) The earthquake mortality rate distribution of the under-50-year-old age group exhibits a constant occurrence pattern, and that of the over-50-year-old age group exhibits an increasing occurrence pattern. (2) The high ratio of the aged living in relatively old houses is one of the reasons resulting in the higher mortality rate of the aged than that of the young.

The damaged areas of the 2003 Bam, Iran, earthquake were detected using 15-meter-resolution satellite imagery acquired by Terra-ASTER. First, fluctuation of digital numbers was modeled as a normal random variable based on 17 pre-event images on a pixel-by-pixel basis. Then, the deviation value of each digital number in the post-event image was evaluated and converted into the confidence level, which indicates the possibility of an abnormal ground surface change. The detected damaged areas were verified with a highresolution satellite image and it was observed that the areas with earthquake influence were mostly identified. However, the pixels with significant change were induced not only from heavily damaged buildings but also dusty roads, possibly due to demolition work. It was suggested that prior knowledge like a high-resolution pre-event image would assist the interpretation of the detected result.

A damage detection method using middle-resolution satellite images, the Image Fluctuation Model method, is proposed, which employs a stochastic model of the digital number (DN) fluctuation in a normal condition and its significance test. The DN fluctuation model is formulated by considering an imaging process of a satellite sensor and an image registration process. A resulting thematic map is created based on a confidence level (12significance level), which is defined on a pixel-by-pixel basis as follows: the minimum significance level at which the null hypothesis, that the pixel DN can be considered as a sample of the DN fluctuation model, is rejected. The confidence level provides the model-based probability of ground surface change. The method is applied to the 2003 Bam, Iran earthquake using images acquired by Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) of Terra. The receiver operating characteristic curves of the method showed better detection performance than temporal image differencing or temporal image ratioing. Though the detection performance of building damage was not comparable to visual inspection on a building basis using high-resolution images of QuickBird, the confidence level map shows similarity at the district level to damage assessment results using high-resolution images.

既存不適格住宅の耐震化の阻害要因は補強技術の問題，居住者の防災意識，家庭事情など多岐にわたる。需要に合致した耐震化推進策が必要である。関東地域の戸建住宅所有者を対象とし，補強工事に関する意識を調査した。家族構成・経済的状況・住宅状態などに応じ，耐震診断・補強関連情報の入手過程を把握した。補強工事の実施意欲に影響を与える要因を明らかにし，住宅所有者による自発的な耐震補強対策の誘導方法について検討した。

This paper discusses the methods to compare the relationship between the strong motion indices and damage of structures. Based on the rank correlation analysis for the dynamic analysis results, it is pointed out that the correlations could change depending on the damage levels and the structural periods. In the nonlinear time history analyses, the responses of wooden structure models of Single-Degree-of-Freedom (SDOF) were simulated for nine hundred input motions. It is observed that the responses of the linear SDOF systems with 20% damping ratio and with elongated periods, considering the damage thresholds, show fairly good correlation with the damages.

Seismic risk management programs for homeowners in Japan are reviewed from a viewpoint of effectiveness of risk communication. Past studies have revealed that it is quite important not only to provide reliable risk information, but also to promote the communication with others for information exchange. In addition, a more effective approach would be based on collective behavior rather than expecting individual preparedness activities in Japan. To improve the risk communication and prompt the risk management action, a program of community-level retrofitting activities is proposed that would avoid fear of dishonest contractors, enhance interaction among homeowners exchanging information, and integrate retrofitting work of a single house into revival of urban areas addressing an inner city problem by group demolition and reconstruction.

A strong earthquake of magnitude 6.8 struck the Mediterranean coast of Algeria on May 21, 2003 and the cities of Boumerdes and Zemmouri were most heavily damaged. QuickBird satellite observed these areas before and after the earthquake. Based on these images, the present authors performed visual damage detection of buildings. Using the post-event pan-sharpened image only, totally collapsed buildings, partially collapsed buildings, and buildings surrounded by debris were identified. Some buildings were difficult to judge their damage levels, and thus, the pre-event image was also employed as a reference to judge the damage status. By this visual inspection, a total 3,446 buildings were classified in Boumerdes and 1,399 buildings in Zemmouri based on their damage grades. The locations of refugee tents in the two post-event images were also identified. These observations indicate that high-resolution satellite images can provide quite useful information to emergency management after natural disasters.

The regional difference of seismic capacity of wooden houses in Japan is revealed based on the seismic diagnosis data. The new vulnerability functions of wooden houses, which use the results of seismic diagnosis and an acceleration response spectrum, are proposed. They employ a probability density function of seismic performance indices of wooden houses, which are separated into an index of the resistance force and other indices regarding the degradation of resistance force. The input seismic motion is evaluated based on an acceleration response spectrum and natural periods determined by the indices of resistance force. The application results to the 1995 Hyogo-ken Nanbu earthquake are compared with the damage statistics at the five sites, which have seismic records. Though the proposed vulnerability functions are not based on the damage statistics, the estimated damage ratios coincide fairly well with the actual damage surveyed by local governments.

The disaster information system, the Early Damaged Area Estimation System (EDES), was developed to estimate damaged areas of natural disaster using the night-time imagery of the Defense Meteorological Satellite Program Operational Linescan System (DMSP-OLS). The system employs two estimation methods to detect the city lights loss or reduction as possible impacted areas; one is the bi-temporal images (BTI) method and the other is the time-series images (TSI) method. Both methods are based on significance tests assuming that brightness of city lights fluctuates as normal random variables, and the BTI method is simplified by introducing the assumption that the standard deviation of city lights fluctuation is constant. The validity of the estimation method is discussed based on the result of the application to the 2001 Western India earthquake disaster. The estimation results identify the damaged areas distant from the epicentre fairly well, especially when using the TSI method. The system is designed to estimate the global urban damage and to provide geographic information through the Internet within 24 h after a severe disaster event. The information is expected to support the disaster response and relief activities of governments and non-governmental organizations.

A new damage or change detection method using middle-resolution satellite images is proposed, which employs the probability distribution model of the digital number (DN) fluctuation in a normal condition and its significance test. The DN fluctuation model is formulated by considering imaging process of a satellite sensor and image registration process. The result thematic map is created from the significance level to reject the null hypothesis that the pixel DN can be considered as a sample of the DN fluctuation model. The method overcomes the threshold setting problem in conventional change detection methods.

The questionnaire survey on subsidies for seismic diagnosis of private housing was carried out for prefectures and major cities in Japan as of January 2003. The result revealed that 30% of prefectures and 60% of major cities have the subsidies. Though the free-of-charge system gathers more than 100 subsidy users a month, even a small burden charge influences the number of users. The law systems regarding seismic capacity evaluation are reviewed on their purposes and evaluation methods. It is pointed out that the qualified results of seismic diagnosis funded by the subsidies should be used for the discount of earthquake insurance, and the seismic performance should also be certificated for the insurance discount after the retrofit works.

The effective international disaster response and relief in a large-scale disaster such as the earthquakes in Turkey and Taiwan become possible by the effective distribution of limited resources, both human and physical. Therefore, identifying the spatial distribution of damaged areas is essential on first step. A method for the early identification of earthquake damaged areas is proposed based on night-light data obtained by the US DMSP (Defense Meteorological Satellite Program)-OLS (Operational Linescan System). The significance in the data of night-light intensity between before and after the reduction in Marmara earthquake disaster in Turkey on August 17, 1999 can be used to estimate possible impacted areas.

In order to reduce human casualties and to set up a correct estimation of death caused by earthquake, it is important to make clear the related factors effecting human casualty. This study focused on Nishinomiya City, which was one of the most heavily damaged city in the 1995 Hanshin-Awaji Earthquake Disaster and a construction of age and sex of the dead is investigated. The investigations prompted two conclusions: (1) The distribution of the earthquake mortality rate of the under-50-year-old age group exhibits a constant occurrence pattern of Weibull distribution, and that of the over-50-year-old age group exhibits an increasing occurrence pattern. (2) The high ratio of the aged living in relatively old houses is one of the reasons resulting in the higher mortality rate of the aged than that of the young.

Characteristics of damage ratio data were discussed using GIS data of buildings damaged by the 1995 Hyogo-ken Nanbu Earthquake. A regression analysis of the damage ratio for two kinds of area unit showed that damage ratios reported by Kobe University were about 60% of those reported by Building Research Institute. An analysis of damage ratios according to different cell areas revealed that the adequate cell size for data collection ranges from 10,000 to 200,000 m^2 from the viewpoints of the number of target buildings in the unit and the resolution level for the damage distribution.

A loss estimation system for earthquake hazard capable of evaluating all of Japan was developed. A GIS (Geographic Information System) for personal computers is utilized for this system, which assists in interactive selection of the assumed earthquake and representation of the estimated results on a computer screen. Source parameters of the assumed earthquake can be derived from a database of active faults and historical earthquakes. Earthquake ground motion, liquefaction and earthquake-triggered fire are considered in order to estimate building damage ratios. An insurance company's exposure can quickly be estimated by linking this system to an insurance contract database.

A method is presented for finding the optimal configuration of a double-layer space truss described by a parametric surface. The number of design variables is drastically reduced, without sacrificing the smoothness of the upper layer surface, by using the control net parameters as design variables. The coordinates of the lower nodes are defined by using a vertical or normal offset vectors from the upper surface. Curvatures of the curve associated with the lower polygon are calculated for evaluating feasibility and regularity of the a double-layer lattice space truss. In the examples, a feasible optimum design, which minimizes compliance under constraints on structural volume, are successfully found by using the proposed method. It is shown that the optimal solutions strongly depend on the specified ratios of the cross-sectional areas of the members.