The Southern Hyogo Prefectural Earthquake (M=7.2, epicenter: 34.36°N, 135.0.2°E, depth =17.9km) occurred on January 17, 1995, and made the Nojima fault appear on the ground surface on Awaji Island. The Geographical Survey Institute surveyed the fault just after the earthquake on January 18-22 and February 13-17. The fault was a right-lateral fault with a reverse component. The maximum displacement measured on the ground along the fault was 1.7 meters in the horizontal (rightlateral) and 1.3 meters in the vertical direction in Nojima-Hirabayashi. The detailed measurement of ground surface displacement around a fault has been only available in terms of the relative movement of one side of the fault against the other. The authors succeeded in measuring three dimensional displacement of 880 points around the Nojima fault by employing air photos taken before and after the earthquake. The characteristics of the displacement are: l) on the west side of the fault, the maximum horizontal displacement is 3.4 meters and directed toward the east, but the amount and direction of the vertical displacement change in a complex manner; 2) the horizontal displacement on the east side is more than one meter and directed toward the south or southeast. In addition, large displacement can be found even in areas more than one kilometer from the fault line. The displacement patterns around the fault are considered consistent with those caused by eastwest compression with eastward movement on the west side and southward movement on the east side: The ground survey identified the southern end of the fault at Toshima. However, the horizontal displacement around the fault can be considered to show invisible continuation of the fault down to Tonouchi
This paper outlines the water chemistry and stable carbon isotopes of water collected from Kobe city and an adjacent area where the so-called seismic damage belt appeared due to the Southern Hyogo Prefectural Earthquake of 1995. Based on the borehole data, a high-temperature anomaly of groundwater is recognized in Kobe and Amagasaki, trending in a northeast to southwest direction. This direction roughly coincides with that of active faults around the Rokko Mountains. From the water chemistry, Cl ion and total CO2 are relatively rich in high-temperature groundwater, which resembles the typical features of hot water from the Arima Hot Springs about 10 km north of downtown Kobe. Furthermore, the values of the stable carbon isotope ratio (δ13C) indicate that the high-temperature groundwater contains carbonate originating from the hot water of deeper aquifers. It is inferred that a hot water reservoir underlies the Kobe area and that the high-temperature anomaly of groundwater is formed by a mixture of shallow groundwater and deep hot water ascending through unknown concealed faults.
In the area damaged by the earthquake in the southern part of Hyogo Prefecture, it is easy to see numerous slope disasters as a result of residential development on the slopes or at the foot of mountains. In almost all of these developments, natural topographical features (hills and valleys) have been artificially transformed into smooth land. The author cites Some examples of some damaged dwellings on the slopes or at the foot of mountains in Kobe City, Nishinomiya City, Takarazuka City and Itami City. These examples are analyzed from the point of view of geological structure, conditions of topographical features, and method of development. It is obvious that the relationship between urbanization and natural conditions generated such damage. The earthquake made clear the danger of development on slope areas. As the result of investigations, it is concluded that the damage to dwellings can be classified into four types: 1) cases affected by topographical features before development, where dwellings were built on former rivers or valleys; 2) cases affected by the method of construction, where dwellings were built on the boundary be tween banking and cutting; 3) slope destruction of weathered granite or secondary sediment, where dwellings were damaged by falling sand and rocks; and 4) damaged dwellings built on lots raised high above ground level on deep filled-in soil. The difference between type 2 and type 4, can be seen in the degree of base wall destruction. In type 3, the cause was the method of fixing the cliff wall rather than in construction of dwelling foundations. Thus the same kind of damage could occur even after a heavy rain. In conclusion, dwelling foundations and topographical features are both important in the occurrencee of damage as well as the impact of an earthquake itself.
There are many farm ponds in the western part of Japan and they play important and essential roles in rice field agriculture. Hyogo Prefecture has 51, 679 farm ponds, the most of any Japanese prefecture. Of the farm ponds in Hyogo Prefecture, 1, 372 were damaged by the Southern Hyogo Prefectural Earthquake on January 17, 1995. The author attempted to clarify the geographical features of those damaged farm ponds. First research was conducted on relationships between damaged farm ponds in Hyogo Prefecture, excluding Awaji Island, and their topography, geology and structure. Damaged farm ponds are located on valley plains, terraces, small fans and boundaries between two topographies, for example, terrace and valley plain, terrace and back marsh, etc. The subsurface geology of damaged farm ponds are Holocene deposits, terrace deposits (Pleistocene deposits), Osaka Group (Pleistocene deposits), Kobe Group (Pleistocene deposits) and Arima Group (Miocene deposits). Furthermore, they are classified by structure as valley closed ponds (tani-ike in Japanese) that enclose valley plains with embankments and flat ponds (sara-ike) that are surrounded by large embankments on an almost fiat surface. Farm ponds located on valley plains of which the subsurface geology is Holocene deposits are very easily damaged during an earthquake, because their bottom gradients are steep and their grounds are weak or unstable. Next, the author conducted research for owners of damaged farm ponds to clarify their superannuation and history of repair. It was found that most severely damaged farm ponds were old and had not been repaired for many years. Few of the old ponds were only slightly damaged or undamaged. Farm ponds that were built more than 200 years ago and have not been repaired in the past 50 years are very susceptible to earthquake damage.
The Southern Hyogo Prefectural Earthquake caused damage of various kinds in Kobe City. Supplies of electricity, gas, and water immediately came to a full stop. Roads and railways were destroyed. Administrative control functions of the single-center system were paralyzed and organization of rescue activities by small communities became necessary. This article aims to investigate emergency water supply systems in the sake-brewing areas of Kobe and to propose the necessity for local control systems and preservation of water resources. Sake-brewing industries are located on recent alluvial fan areas with rich groundwater resources. Groundwater is drawn from many wells located throughout these regions. The regions under study, Nada-nishi-sango, belong to the outer transitional areas, bordered by residential districts on the north, and by reclaimed industrial-use land on the south. The land use is a mix of residential, industrial, and commercial functions. Under the difficult conditions of heavy damage, sake brewerers used their resources to supply emergency water to help quake victims. Just after the earthquake, water preserved in tanks for use in sake brewing was supplied. Next, water from wells and after that water from the city's special water supply system for the exclusive use of the sake breweries was utilized. The quantity and quality of water from all wells were inspected regularly under the meticulous control of the sake brewers' union. In 1973, the brewers' union funded construction of the city's special water supply system for the union's exclusive use, as a countermeasure against a possible decline of groundwater due to the development of surrounding areas. This emergency water supply to neighboring victims, evacuation centers, and hospitals continued from January 17th to early March. It is recommended that the city's renewal plan adopts the following proposals. Large quantities of water are needed after an earthquake in a metropolitan area, and water reservoirs for such needs should be built and controlled by small communities for easy access. Kobe has good groundwater resources, but such resources are in danger of deterioration due to destruction of the natural environment accompanied by regional development. As seen in the example of sake-brewing areas, networks based on small area units should be prepared as measures against disasters. Future tasks should include inspection and preservation of old wells no longer being used. In transitional areas of large cities, rapid industrial growth typical of harbor cities has caused deterioration of both the social and natural environments. The government's delay in making needed improvements, compounded by an expanding aged population and by the large number of rotting old wooden dwellings, intensified the losses caused by the earthquake. In land use planning for the city's renewal, preservation of the natural environment and improvement of the social environment should be kept in mind.
The Southern Hyogo Prefectural Earthquake which occurred on January 17, 1995, caused enormous damage such as collapse of buildings, fires, liquefaction of the ground, etc. It was the worst disaster since the Great Kanto Earthquake of 1923. The Geographical Survey Institute (GSI) started taking color aerial photographs immediately after the earthquake and drew an Earthquake Damage Map (First Edition; Map I) by photo interpretation, for the purpose of preparing fundamental data for investigation and restoration. Items included in Earthquake Damage Map I were “collapsed buildings and houses, ”“fires (burnt areas), ” “damaged roads and railroads, ” “slope failure and landslides, ” “liquefaction of the ground, ” “damaged quay, ”and“earthquake faults.”After that, other organaizations started similar investigations. In drawing the Earthquake Damage Map (Second Edition; Map II), the investigated areas were extended and other data were also used. Items included fundamentally followed Map I, although “collapsed buildings and houses” were newly classified into four categories, and two new items, “suspended sections of damaged roads and railroads, ” and “fissures” were added. Earthquake Damage Map I drawn up and utilized immediately after the earthquake was highly esteemed. After that, investigations by other organizations showed earthquake damage similar to that in Earthquake Damage Map I. Therefore, the accuracy of Map I was confirmed. We examined the items included, and method of publication and prarctical use in the process of drawing up Earthquake Damage Map. It was found that photo interpretation of “fire (burnt areas), ” “damaged roads and railroads, ” and “liquefaction of the ground, ” was fairly easy, but that of “collapsed buildings and houses” and “slope failures and landslides” was comparatively difficult. Thus we recognized the limits of photo interpretation ability. By drawing a distribution map of each kind of disaster based on the Earthquake Damage Maps, it was obvious that damaged buildings were mainly distributed in a zone from Suma Ward, Kobe City, to Nishinomiya City. We examined the relationship between damaged buildings, houses and landform. As a result, it was hypothesized that the primary factor in the damage concentration area was mainly earthquake motion because there was little influence of structures, landform and topography. After the Southern Hyogo Prefectural Earthquake we recognized that it is very important to collect and publish information on damage quickly in an emergency. The GIS and the Internet were utlized in this earthquake disaster. Therefore, it is expected that new technology will be utilized more extensively in the future.
The damage caused by an earthquakes does not relate only to the conditions of the natural environment. After the Southern Hyogo Prefectural Earthquake of 1995, many natural scientists addressed the spatial features of the damage, which formed a “belt” between the coastline and the mountains. But the damage was also caused by human and social conditions, related to the urban structure. This kind of situation which is affected by many kinds of natural and social conditions in each region, is studied using a geographic information system (GIS). Analyzing urban earthquake disasters using GIS may also be useful to simulate potential damage for disaster preventation in other cities. The final purpose of this research therefore is to develop such a method of GIS. The most appropriate spatial unit to analyze earthquake damage is the town district. Architects have already started to analyze the unit of individual building but this approach has some problems: The data and work volumes are huge and a large GIS is needed, so that we cannot develop such a brief system for use in other areas easily; Precise data on each buildings are private information and thus not easy to access; And spatial location is not crucial to the analysis of architectural structures. Consequently, the unit of a town district is a more convenient approach from the viewpoint of urban structure or urban planning. It can also include community data and so contribute to urban planning directly, for example, regarding the location of open space. In the case of Higashinada Ward in the eastern part of Kobe City, which recorded the largest number of persons killed by the earthquake, a “belt” of damaged buildings was found and studied by many natural scientists. Some assumed that a new hidden fault line existed along the belt. But the urban structure of Kobe City itself comprises a “belt” structure. Thus, before searching for such a fault line, we, need to analyze the relationship between urban structure and _disasters using data sources on the damage. There are maps of the distribution of damaged buildings, as recorded by City Planning Institute of Japan and Architectural Institute of Japan, and data from newspapers on the location of fatalities. We can also use general data sources regarding urbanization, for example, maps, aerophotos, and census data, because we need to be able to apply the same system in other cities. As shown in Fig.l, the damage is different even inside the “belt.” Generally, the collapse rate of building was extremely high in the built-up area in 1948, which suvived bombing during World War II. There were also some damaged districts near the coast outside the “belt, ” because of the same reason. Most areas along the coast were bombed and burned in World War II, so the buildings were rebuilt and relatively newer there, and were not severely damaged. In some old districts, many buildings were rebuilt after World War II for example, in the district along R. 43 which is the main industrial road between Osaka and Kobe. At the foot of the mountains in the north of this area, few old buildings were damaged sumed to be due to good topological conditions and the higher social class of the residents. In the eastern part of this area, many districts that were urbanized after World War II were severely damaged, because here were built many low-cost, cheap wooden apartments for young workers as shown in Fig. 2. Figure 3 shows that high death-rate districts correspond to the severely damaged districts shown in Fig. 1, and that not all the districts where many elderly people lived (Fig. 4) had a high death rate of the elderly, due to the superior conditions of the buildings. GIS analysis is very effective in studying the spatial factors of disasters in urban areas where complicated elements exist.