Published papers

The relationship between building damage patterns and human casualties in Nishinomiya City - one of the most heavily damaged cities in the 1995 Hanshin-Awaji Earthquake Disaster - was investigated using photographs of damaged buildings. First, the photographs of buildings in which casualties occurred were identified, and the building damage patterns were judged based on the photographs considering the existence of survival space. Then the relationship between the building damage pattern and casualty occurrence, and the characteristics of casualty distribution, were investigated. The main findings were as follows: Most casualties occurred in relatively old two-story wooden buildings in which the ground floor completely collapsed without survival space; casualties occurred at all building damage levels including "no damage", and it can be seen that building damage is the major, but not the sole cause, of casualties in an earthquake; in Nishinomiya City, the regional distributions of casualties due to the collapse of buildings that left no survival space is similar to that of casualties due to other types of building damage.

Rebuilding of victims' livelihoods was a crucial issue in the restoration process in the1995 Hanshin-Awaji Earthquake Disaster. Housing damage assessment influenced most of the rebuilding of the livelihood in the long term, because the Victim Certificates issued by the local governments based on the results of the Housing damage assessment was required to receive most of the individual assistance measures. In the process of Housing damage assessment, many complex problems arose, leading to extensive work on the part of the disaster responders. Consequently, a considerable number of victims were dissatisfied with the assessment and applied for a resurvey. Due to a flood of requests for resurvey, disaster responders had to work on damage assessment, leaving relief activities aside. In order to facilitate Housing damage assessment, this paper discusses the following five points: (1) the processes and the problems of assessments performed in the Hanshin-Awaji Earthquake Disaster, (2) the changes in the nature of information needed by the victims, (3) the improvements over the present damage assessment, (4) the housing situation in Japan, and (5) the international situation on damage assessment. It is obvious from the results that a poor damage assessment system and the size of the disaster produced a very large work load. Differences in appreciation among the investigators also contributed to unfair assessments and led to the victims being increasingly dissatisfied by the survey results. Finally, a design concept for a comprehensive damage assessment system, which has been derived from the above five points, is proposed for post-disaster management.

Recently, many private and public sectors have provided methods of seismic diagnosis for wooden housing on their Web pages. Since the Internet can easily gather a large number of participants, it is expected that these Web pages will promote house owners to recognize earthquake risks, to carry out the retrofit works, and to join to earthquake insurance. This paper proposes an effective and adequate method for seismic diagnosis of wooden houses through the Internet. First, a questionnaire was carried out to wooden-house owners in Tokyo with the simple diagnosis method that is widely adopted in Japan. Secondly, experts visited and inspected the houses by two methods: the simple method, and an in-depth more accurate method, which calculates eccentricity and story stiffness based on the wall materials and allocations. Finally, three diagnosis results were compared. The results revealed that the owners, who are non-experts, returned the diagnosis results diverging from that of experts while the results of the simple and the accurate methods by the experts matched fairly well. Thus, the simple method itself is effective, but in order to improve non-expert result, the followings are suggested: a) provide a land condition (geologic and geomorphologic) database, b) present sample photographs of foundation cracks to prompt them to check carefully before their diagnosis, c) indicate alternatives of wall length along with a house plan and consider a roof type, d) add the questionnaire entry on types of inner and outer walls, and e) add the questionnaire entries on the second-floor area and the center of gravity.

The purpose of this study is to investigate the structure of earthquake risk awareness of residents through analysis on a questionnaire survey in the two districts in Tokyo: Setagaya and Sumida, which are typical residential districts from the viewpoint of urban housing planning. Our study focuses on the relation of the risk awareness of residents and the actual risk of their house, and the preference of the alternative to reduce their risk. In this paper, we clarified the differences dependent on the local characteristics and the universality in these two districts to regard as important, in considering the measure for mitigation planning, earthquake insurance and retrofit of house, and abstracted some points to analyze on in detail in the following study.

The regionality of seismic performance indices is analyzed based on the results of seismic capacity evaluation employed to buildings of all over Japan. The evaluation results are aggregated into eight regions: Tohoku, Kanto, Hokushinetsu, Chubu, Kansai, Sanyo, Shikoku, and Kyushu, considering culture and climate. The distributions of the construction year and total area of floor space are examined of their similarity to those of Housing and Land Survey taken by the Statistics Bureau of Japan. Buildings in Tohoku show the lowest performance indices in eccentricity, but the highest in horizontal resistance. The ratio of buildings with construction year older than 1981 and area less than 50 m2 should be adjusted to that of the survey result because they have poor performance indices.

In the present methods to estimate buildings’ damage due to an earthquake, empirical fragility curves based on damage statistics are mostly employed. The structural type and construction period were considered in developing them, but regional characteristics were not considered well. The objective of this study is to analyze the results of seismic capacity evaluation conducted in two cities, Yokohama and Himeji, for more accurate damage estimation. From the analysis of the data, it is observed that there are significant differences in the seismic performance of the buildings in the two cities even though they have the similar structural type and construction period.

The wooden housing damage due to the 2000 Tottoriken Seibu Earthquake was analyzed using the damage survey data investigated by Yonago City. It was clarified that the actual housing damage ratios are lower than estimated results based on simulated peak ground velocity and fragility curves that were derived from the data of the 1995 Hyogo-ken Nanbu Earthquake. Damage mode, which is combination of roof, wall, and structure damage ratios and tilting levels, were calculated for each topographically classified area, and its regional trend was revealed.

Recently, the Institute of Industrial Science of the University of Tokyo has been moved from Roppongi Campus to Komaba Research Campus. In the relocation, seismic observation system was newly set up in the institute's building, on the ground surface, and in a borehole. The observation system has collected the records from six seismic events. On the basis of these records, site and building responses were analyzed. The results showed general characteristics of the seismic response in the urban center of Tokyo, particularly, the site amplification due to sediments over Tokyo Formation. A particular soil anisotropy was found around 4.2 Hz due to the soil-structure interaction. In the future, more observation records will be collected and it is expected that the data may provide the details of the site and building response characteristics.

A strong earthquake hit El Salvador on January 13, 2001. The earthquake with a magnitude of 7.6 caused huge damage in the urbanized areas as well as numerous landslides. In case of large scale earthquakes, the identification of hard hit areas is important and necessary information for decision-makers to handle the disaster relief process. In this study, remote sensing images taken before and after the earthquake by Landsat 7 (ETM+) satellite are compared to identify the location of landslides and hard hit urban areas. The proposed method uses the rationing between bands in the visible range as well as the sharpening of the multi-spectral bands by merging with the panchromatic band. It is expected that with the help of this additional band the identification of landslides and damaged areas will be improved.

The buildings properties in spatial databases are very useful for urban planning, disaster mitigation, insurance business etc. But the databases in some governments are not freely available since they include private information. Therefore, the data acquisition mostly depends on image interpretation of photographs and field surveys. Consequently it is time-and labor-consuming and very costly to construct databases, and it is not easy to maintain the data up-to-date and to employ them in wide use. In this study, automatic detection method of building properties based on aerial photographs is proposed and the result is verified by the database made in a conventional way of data acquisition. The method consists of the following steps: (1) geometric correction and gray scale conversion of aerial photographs, (2) stereo matching and evaluation of building heights, (3) evaluation of building areas, (4) color and texture analysis, and (5) classification of buildings. Buildings are classified into the following categories: (a) detached houses, apartment buildings and multi-storied buildings. (b) wooden and non-wooden buildings. The method is applied for a target area in Tokyo and the result is compared with the ground truth data investigated by the authors and the database provided by of Tokyo Metropolitan Government. As a result, it is found that low-storied apartment buildings and multi-storied buildings are correctly identified and they can be classified into proper structural types.

This paper proposes the method to develop a high-resolution image of urban properties from frequently observed low-resolution images based on the statistic process assuming urban properties have little temporal change. Because disaster responders sometimes have difficulty to obtain the map data in a digital form especially in developing countries, it is well known that satellite imagery and aerial photographs can support disaster response and rescue activities. But high-resolution images that can provide roads and buildings information expense considerably high when acquiring wide range data by means of aerial photographs or imagery of recently launched satellites with high-resolution sensors. On the other hand, satellite images of spatial resolution of 10 to 100 meter order cost comparatively low. The paper discusses the number of low-resolution images to develop a high-resolution image. First, a one-meter-resolution image derived from an aerial photograph is used as a truth image. Three-meter-resolution image is also evaluated as a reference high-resolution image. Secondly, a nine-meter-resolution image, which simulates an image scanned by a low-resolution sensor of satellites, is evaluated with a randomly selected offset of scan line. The same cell size as a reference image, i.e. three meter is employed for the low-resolution images. Thirdly, a resolution-improved image is synthesized from the average and standard deviation based on each pixel calculation of the simulated images. Then the difference between the reference image and synthesized image is evaluated. Finally, the relationship between the number of low-resolution images and the standard deviation of differences of all pixels in the average image is analyzed. The result quantitatively clarifies that a high-resolution image of urban properties with little temporal change can be developed with a sufficient number of low-resolution images when the precise geolocation is guaranteed.

The new method is proposed to estimate damaged areas using the Defense Meteorological Satellite Program's Operational Linescan System (DMSP/OLS) nighttime imagery for the Early Damaged Area Estimation System (EDES). The former method uses two-acquisition-date images of pre- and post-events, but it has problems of weakness for cloud influence, misdetection of damaged areas due to water reflection of city lights, and tendency to neglect damages in small towns. To address these problems, the proposed method employs significant tests on a pixel basis based on each pixel's average and standard deviation, which are evaluated from time-series images during gain stable periods around new moon phases.

Damage Assessment Training System (DATS), which consists of an effective damage assessment system and a training system for its use, is proposed to enhance awareness and skills of disaster responders. DATS is designed based on the analysis of building damage assessment performed following the 1995 Hanshin-Awaji Earthquake Disaster. It integrates several improvements over the building damage assessment methods currently in place, and should provide information on housing damages in a much more timely fashion. It is aimed at expediting the work involved in disaster response, therefore, disaster responders would be relieved from the extensive work of damage assessment and should be able to devote themselves to higher-quality service for livelihood rebuilding of victims.

The authors are developing the Early Damaged Area Estimation System (EDES), which provides the information as to the estimated impacted areas after any significant earthquake based on nighttime lights observed by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). The estimation method is based on the detection of significant reductions or loss of lights in nighttime images following the event, for it can be expected that city lights will observably decrease after a large earthquake. In the 1999 Taiwan Chi-Chi Earthquake Disaster, there was a countrywide power cut due to the damage of the transmission facilities in Chungliao and Tienlun. The post-event image seems to reflect this influence in appearance compared with a pre-event image, but the further investigation is needed because the gain setting of OLS changes along with lunar phase and elevation, and visible-near infrared (VNIR) band imagery only provides relative light intensity. This paper presents a new method to estimate damaged areas based on a radiance-calibrated image and a method to estimate gain and radiance of observed VNIR imagery, and the validity of the estimation result of EDES application to the Chi-Chi Earthquake is discussed using the electric load data before and after the earthquake.

The Early Damaged Area Estimation System (EDES) is proposed to support emergency response in a disaster. EDES provides the geographic information of possible impacted areas within 24 hours after an earthquake on the Internet The estimation method is based on the detection of significant reductions or loss of lights in nighttime imagery observed by the Defense Meteorological Satellite Program's Operational Linescan System (DMSP/OLS). Noise in suburban areas and cloud influence in a pre-event image are addressed by using a cloud-free stable lights image derived from a time series of OLS observations. Appropriate geographic information is discussed to support relief activities and to contribute a reduction in the digital divide problem in global disaster management activities.

In the Hanshin-Awaji earthquake disaster, the lack of information about where the earthquake damaged areas were prevented early and effective emergency responses and relief. Since then, the national and some local governments in Japan have developed GIS-based damage estimation systems, but few other countries have such systems as yet. Nighttime city lights decreased significantly after a large earthquake, and the DMSP/OLS imagery is suitable for the early estimation of the damaged areas. The damaged areas of the 1999 Kocaeli earthquake in Turkey and 1999 Ji-Ji earthquake in Taiwan were estimated by using DMSP, and the results showed a good match with the real reported damage. We propose a new program through international collaboration to support emergency response and relief activities by providing information as to the estimated impacted areas within the first 24 hours after any significant earthquake. This program consists of the following steps: (1) acquire the earthquake hypocenter data through the Internet, which is for example announced by the USGS. (2) Determine the sampled area of the images by the attenuation formula of earthquake ground motion. (3) Obtain corresponding both time-wise and area-wise DMSP/OLS nighttime images from NOAA/NGDC. (4) Estimate the damaged areas by analyzing the statistically significant decrease in the light intensity of the images. (5) Create a thematic map to present the estimation results as geographic information. (6) Disseminate the resulting map widely and quickly through the WWW.

After the Marmara earthquake disaster in Turkey (Aug.1999), Kohiyama et al. proposed a method to estimate the impacted area of the earthquake using visible and near-infrared (VNIR) satellite imagery provided by the Defense Meteorological Satellite Program's Operational Linescan System (DMSP/OLS), and succeeded in estimating the impacted area of the Marmara earthquake disaster and the Ji-ji earthquake disaster in Taiwan (Sep. 1999) based on their method. They assumed that the brightness of the area would decrease if the buildings collapsed or blackout occurred due to the earthquake. Then, those areas whose brightness decreased significantly after the earthquake compared with before the earthquake were estimated as the impacted area. The purpose of the present study is to check the validity of the above mentioned method by the application for the Hanshin-Awaji Earthquake (05:46 Jan. 17, 1995) in which the more detailed and various types of damage data due to the earthquake are available as compared with the verification in Turkey.

Effective damage assessment in terms of disaster management is proposed, which consists of both visual survey based on damage patterns of buildings for prompt service and resurvey for citizen's assent to the assessed damage. Problems which Nishinomiya City encountered in issuing certification of building damage reveals an extent of visual survey and necessity of resurvey in issuing process. Difference between two visual surveys of buildings damaged by the Hanshin-Awaji Earthquake Disaster in Tsukiji District, Amagasaki City shows difficulty in finding differential settlement caused by liquefaction and integrated damage patterns of buildings are proposed for effective field investigation.

It is found from the questionnaire about the victim’s need for information regarding livability and house repair that the victims needs the information about housing options at the first one week after the Great Hanshin-Awaji Earthquake. However, Building Safety Evaluation, which was the first damage assessment for the individual houses, conducted 6 days after the earthquake from January 23rd to February 9th, 1995. The information needs of the victims cannot be sufficiently fulfilled. The building damage assessment must be conducted both quickly and exactly. It is conceivable that building damage survey using the damage chart is effective. This paper evaluates the effectiveness of the damage chart for damage assessment, and classifies photographic data that are linked to the geographic information systems (GIS) database of Nishinomiya City, based on the damage chart. In addition, we develop the damage chart of wooden structures affected by liquefaction from the case of Amagasaki City.

Fragility functions of buildings, which show the relation between seismic intensity and building damage ratio, are used for estimation of building damage caused by an earthquake. Fragility functions are formulated statistically by data of seismic intensity and building damage ratio on cell units and area size of the cells should be considered to calculate damage ratios. In this paper, the characteristics of damage ratio data are discussed using GIS (geographic information system) data of buildings damaged by the 1995 Hyogo-ken Nanbu Earthquake. First, the two databases of the different parties, which concerns buildings damaged by the earthquake, were compared in terms of the method of each survey and their criteria of damage ranking. It was found that the criteria of damage ranking of the two databases do not differ much, but numbers of damaged buildings and the damage ratios in each rank differ remarkably from each other. Secondly, based on the damage ratios in terms of various cell sizes, it is pointed out that the adequate cell size ranges from 10,000 m2 to 200,000 m2 from the viewpoints of the number of target buildings in the unit and the resolution of the damage distribution.