The Rokko Mountains, which extend from east to west, divide Kobe City into northern and southern sides, The south side faces Osaka Bay and lies on a long and narrow plateau stretching east to west (formed by sediment transported through the Omote-Rokko rivers from the Rokko Mountains) as well as on coastal lowlands. The steep hills of the south side of the Rokko Mountains have many valleys and face the urban areas. The hills are connected to large sediment deposits along the Suwayama faults.
Approximately 70% of the city’s population lives in the urban areas.
Undulating hills over 300 m high made up of rhyolite and tertiary deposits are located on the north side of the Rokko Mountains. The west side of the city is situated on a low plateau made up of quaternary deposits created by the Ikawa River and other rivers, and it is adjacent to the western plain.
(1) Earthquake risk
Kobe’s urban areas are situated at the verge of Rokko Mountains (which are gradually elevated by crustal movements called the Rokko movements) and Osaka Bay (which has been sinking since the Quaternary Period, approximately two million years ago). There are active faults including the Suma and Suwayama faults, the Rokko-Awaji fault system, which includes the Kariyaoki, Okurayama, and other concealed active faults (located just southeast of the aforementioned active faults), and the Osaka Bay fault system (located about 5 km south of the aforementioned fault system). The Osaka Bay fault extends from north-northeast to south-southwest in the central-western part of the bay. The northern end of the fault to stretch offshore of Port Island, but it is not clear after that point. In addition, diverging north-northwest from the Osaka Bay fault, the Wada-misaki fault is located at the east end of Wada-misaki Point, extending northeast to join the Rokko-Awaji fault system somewhere between Nada-ku and Higashinada-ku in Kobe City.
Additionally, the Takatsukayama fault is located on the western margin of Mt. Rokko, and the Rokko and Kashiodani faults (extending westward from the Arima-Takatsuki tectonic line) exist near the northern part of the Rokko Mountains and the Taishaku Mountains. However, generally speaking, the faults on the north and west sides of the Rokko Mountains have been less active compared to those on the south side since the latter half of the Quaternary Period, and most of their movements have been insignificant.
(2) Great Hanshin-Awaji Earthquake
i) Characteristics of the 1995 Southern Hyogo Prefecture Earthquake
a. The earthquake directly hit the Hanshin metropolitan area, including Kobe City (7.3 on JMA magnitude scale)
b. The earthquake originated at a relatively shallow depth of 16 km and caused destruction in a vertical and an almost rectangular area (50 km long and 15 km deep) instantaneously releasing great energy. The duration of the earthquake was short, but the oscillation was the largest on record at 18 cm, which caused a never-before-experienced catastrophe.
a. The earthquake caused the most destruction of any earthquake since the 1923 Great Kanto Earthquake, including 4,571 deaths, 2 missing persons, 14,678 injured persons, 122,566 fully or partially collapsed buildings, and 7,045 fully or partially burnt buildings. (These numbers are for Kobe City alone.)
b. The earthquake directly hit the metropolitan area, damaging electricity, water supply and sewage systems, gas, and telephone lines in a wide area as well as cutting off lifelines such as roads and railways.
c. Many buildings collapsed and fires broke out in areas where there were many old wooden houses. On the west side of the city, in particular, fires broke out simultaneously.
d. The earthquake caused substantial damage to large-scale structures because the intensity of the earthquake exceeded our expectations and the structures were not designed to withstand such an earthquake.
e. The earthquake damaged the city hall (Building 2), hospitals, fire stations, and other facilities. Some markets, shopping areas, factories, business offices, and other buildings also collapsed or burnt down, which severely damaged the economic infrastructure.
iii) Major damages (in Kobe City)
Fully collapsed buildings 67,421
Partially collapsed buildings 55,145
Fully burnt buildings 6,965
(Resource: Kobe City Disaster Control Headquarters)
a. Evacuees: 236,899 (at 599 evacuation centers; the number reached its highest on January 24, 1995.)
b. Number of fires: 175 (between January 17 and 27)
c. Area destroyed by fires: Approx. 82 ha
d. Damage to lifelines
Water: The water supply was cut off in the urban areas and beyond instantly after the earthquake occurred. Emergency rehabilitation was completed on April 17.
Sewage: Immediately after the earthquake occurred, some sewage pipe lines were damaged, some treatment facilities stopped working, and some facilities reduced their functions in the urban areas and beyond. Emergency rehabilitation was completed on May 31. Restoration was completed at the end of 2006 (except for the Higashinada treatment facility).
Electricity: The electricity went down in the urban areas and beyond immediately after the earthquake occurred. Emergency rehabilitation was completed on January 23.
Gas: The gas supply stopped immediately after the earthquake occurred. Restoration was declared complete on April 11.
Telephone lines: The telephone lines were disconnected in the urban areas and beyond immediately after the earthquake occurred. Approximately 120,000 lines were declared restored on January 31.
(3) Floods and other risk
Generally speaking, Kobe City belongs to the Setonaikai climate. The south side of the Rokko Mountains has a relatively mild climate due to its proximity to the Seto Inland Sea. In contrast, it is slightly colder on the north side of the mountains due to the higher altitudes.
The Rokko Mountains are a recreational area for Kobe residents. However, from a meteorological perspective, upward air currents develop along the mountains under low atmospheric pressures or ahead of fronts, sometimes causing heavy rain.
The wind blows from the north or west-northwest between September and March due to seasonal winds during winter. Between April and August, the wind blows mainly from the east-northeast along the Rokko Mountains.
Kobe City has an average annual wind speed of 3.2 m/s (based on 1996-2000 figures). The wind condition becomes a critical factor in the occurrence of fires at the time of an earthquake.
15 years ago, Kobe was inflicted with catastrophic damage by The Great HanshhrAwaji Earthquake. From such ruins, Kobe was able to rebuild and recover through the heart warming support received from various nations and regions throughout the world. I would like to take this time to express my sincere gratitude.
Through the massive earthquake experience, we have learned "importance of human life", "appreciation of a circle to help one another", and "the importance of preparing for disaster."
As a reminder of the sacrifices and the lessons ofthe disaster, we are continuing to work towards creating a "safe and secure city."
For manyyears, Kobe has a historyofdealing with flood disasters. After the earthquake, the citizens established a voluntary organization for disaster prevention in communities, BOKOMT (Disaster Safe Welfare Community). With the joint efforts by the city government, Kobe continues to exercise activities for "the next generations to succeed these lessons of the earthquake" and to "prepare for future disaster."
15years has passed since the earthquake. We believe, wemust not allow for such tragic experience to repeat. Unfortunately, at present, it is beyondour powers to stop natural disasters from occurring. But we would be most pleased if our experiences could help assist with reducing the destruction caused by natural disasters.