In Toyonaka City, Osaka, construction work is continuing on a 14-storey apartment building on a site that is directly above an active fault line.
“Uniheim Senri Momoyamadai” is located in Higashi-izumigaoka 3 Chome and is directly above the Butsunenjiyama Fault – an active fault line that runs from the north of Toyonaka and south to Suita in Osaka. It is an extension to the Uemachi Fault, a relatively active fault line which has a 2~3% chance of producing an earthquake within the next 30 years, and a hypothesized magnitude of 7.2 would result in an estimated death toll of 42,000.
A probability of 2~3% is relatively high in comparison to other nearby fault lines such as the Arima-Takatsuki Fault (0~0.02%) and the Rokko-Awaji Fault (0~0.9%). It is also said that the fault line becomes active prior to a Tonankai or Nankai earthquake.
The developer tried to address some of these concerns by holding a meeting with local residents who oppose the new building. At the meeting, the representative for the developer said they were not sure exactly where the fault line was, so they conducted some tests and found that there were none in the area. They also said that the fault is only active one every several hundred years, and that it probably would not be active for the next few decades. Because of this, they chose not to implement any counter-measures for earthquakes into the building design. Out of the 5 levels of earthquake-resistant construction, the building will only be constructed to level 1 (the lowest), and will not have any measures to deal with water seepage.
The layers of stratum visible at the construction site are almost vertical. The removal of trees and lake that were once on the site has meant that the groundwater has nowhere to go and is now seeping up through the soft clay layers and pooling at the surface of the site and in the nearby carpark. The construction company has to continually pump water out of the site. According to Toyonaka City hazard maps, the area is at very high risk of liquefaction. During the 1995 Hanshin Earthquake, the nearby area of Higashi-izumigaoka 1 Chome suffered liquefaction which caused groundwater to erupt in the streets and caused power poles to lean.
Professor Koichi Nakagawa of Osaka City University, analyzed the stratum at the construction site. He said that the vertical stratum is the result of earthquake activity in the past and constructing a building on this type of ground would be very dangerous. A fault rupture would cause the western-side of the site to fall and the eastern side to jolt upwards. This makes the probability of building collapse extremely high. This was seen in earthquakes in Taiwan in 1999 where an apartment building located directly above the fault line was left tilting dangerously.
Due to its proximity to neighboring houses, residents are concerned that it could collapse onto their homes in an earthquake.
Residents submitted a request to Toyonaka City to have the building approval withdrawn. However, the process is very slow and the developer has already finished the foundations on the building.
There are no laws that prohibit construction on top of a known fault line. There are, however, self-governing organizations that try to stop constructing in these areas.
The nearby city of Nishinomiya in Hyogo Prefecture suffered extensive damage in the 1995 Hanshin Earthquake. A representative from Nishinomiya City Council said that they produced very detailed maps of the fault lines following the earthquake. Whenever someone wants to build above one of these fault lines, they are obligated to have an expert undertake in-depth analysis of the site and its proximity to the fault. The planning and development division within the City Council also provide advice to those wishing to build.
Professor Nakagawa is urging Toyonaka City to take a similar stance to Nishonomiya City. As there are over 2000 fault lines across Japan, many of which are in populated areas, it is extremely important that local governments either change the current regulations or implement guidelines regarding construction. Professor Nakagawa also said that while we cannot predict when earthquakes will happen, we can predict potential outcomes and take appropriate counter-active measures.
“????????????????????” MBS Voice Television Program, July 18, 2011. Transcript here: http://www.mbs.jp/voice/special/201107/18_718.shtml
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