GEOLOGY & GEOMORPHOLOGY
At this moment I will explain about the geoenvironmental condition of Sendai City, Japan. Before explain Sendai, I would like to give short description about Japan archipelagos.
Japan situated in the middle of four plates (Eurasion plate, North American plate, Pacific plate, and Philippine Sea plate), according to this situation Japan archipelago is very vulnerable to earthquake and tsunami triggered by it. Their strain energy gradually each year, and will be release the energy simultaneously, we call this mechanism as earthquake.
At the center of Sendai City, the Nagamachi-Rifu fault is located which limit the southeast side of river terraces. The Nagamachi-Rifu fault forms a fault system, including the Dainenji-yama fault and Nigatake blind fault. Based on the deformation of river terraces on the hangging wall, the vertical slip rate of the Nagamachi-Rifu fault was estimated to be more than 0.5 mm/year (Nakata et al., 1976; Otsuki, K. et al., 1977). River terraces are distributed along the Hirose and Nitori Rivers. The river terraces are divided into the Aobayama, Dainohara, Sendai Kamimachi, Sendai Nakamachi, Sendai Shimomachi Terraces, from higher to lower level, based on tephrochronology and comparing the relatives height of the terraces. The alluvial lowland, less than 20 meters, is facing the Sendai bay. Sendai city now prepare for big hit earthquake as expert forecast will be happen in this year (90%), and 99% in the next to years.
The climate in Sendai is influence by mountain (Yamagata) and sea (Pacific ocean). Typhoon also sometimes approaches Sendai. After ending autumn rainy season in mid-October, sunny day increases again. These seasons transition in Sendai is similar to that of whole Japan, while there is regional differences in a timing of beginning or ending of each seasons. Snow falling in begin December, it changes to rain in the beginning of March. In spring, strong wind increases in frequency as the storm track moves towards the north, while snow falling decrease.
The urban heat island is the phenomenon that air temperature in urban area rises higher than that of suburb area. This phenomenon is thought to be caused by urbanization (city development). Anthropogenic heat due to human activity (factory and office building) and the artificial surfaces (building and roads) make the air temperature in a city higher. Temperature distribution in Sendai city and around CBD (Central Business District) of Sendai and hourly temperature and solar radiation in Sendai are given below.
Sendai city was originated from the castle town of Sendai-Han. The term ”Han” means a territory of feudal lord and its ruling organization which is given the sovereignty by Shogun, the supreme lord. Masamune DATE, the first lord of Sendai-Han, founded the castle town in 1600. He constructed his castle on the top of hill (Aoba-Yama) in the right side of Hirose River. And then, the town was built on the alluvial plateau in the left side of the river.
The castle town was a planned city. The lattice road pattern done in an orderly manner. The town is characterized by the strict residential segregation by class. The high class of retainers lived in large size plot near the castle, and the low class of retainers in small size of plot in the firnge of town. Katahira campus of Tohoku University is the side of high class retainer’s residential area. Merchants residential areas were assigned along the main street. The built-up area of the city didn’t extend widely from the area of castle town before 1930s.
The central area of Sendai city was almost burned out by the bombing in the tenth of July, 1945. After world war II the central area was rebuilt under the direction of reconstruction and city-planning projects. The narrow streets were broadened in the central area. Before world war II, the urban economies largely depended on the public sector, so the city was recognized as a public servant’s city (prefectural office, national university, other high education institutes, high court, and army base were agglomerated in Sendai).
After the war Sendai changed its figure to be real central city in Tohoku region. Many branch office of nation-wide companies were established in addition to the agglomeration of branch office of national government. A lot of buildings along with main streets in CBD were constructed to supply rooms for these branch offices. These branches offices play the role of selling base over the whole region of Tohoku, Due ti it, Sendai elevate its centrality in the region. And then the population had also rapidly increased since the 1950s. Furthermore. the share of employees in tertiary industry and white color jobs was higher compared to other cities.
The remarkable expansion of residential areas over hills being situated around the old built-up area of Sendai. These residential areas have been constructed since the late 1950s. In addition, many condominiums were located just like surrounding CBD. These condominiums have been built since 1970s. Recently the number of houses supplied by it exceeded that of detached houses in suburbs.
Concentration of young-age people is around Kawauchi, Katahira, Aobayama, Seiryo, Yagiyama and Amamiya. The reason is many apartment surrounding the Campus of Tohoku University dwelt by students.
At present the problem in Miyagi-ken is aging peoples do not have regeneration for keep the agriculture industry for the future. Because young generation only looking for white color jobs in the big city (Tokyo, Kyoto, Osaka, others).
Material Source: Geoenvironment, Earth Science Dept. Graduate School of Science, Tohoku University.
Acknowledgment: many thanks to my Professor, Masateru HINO for let me edit his manuscript for ‘Sendai City Development’