Inclination of houses induced by liquefaction in the 2018 Hokkaido Iburi-tobu earthquake, Japan
On September 6th, 2018, at 3:07 local time, a strong earthquake of magnitude Mw = 6.6 struck the east Iburi region in Hokkaido, Japan. Many serious damages such as landslide, liquefaction and collapse of houses occurred from this earthquake. Liquefaction caused road deformation and inclination of houses in Sapporo city, Hokkaido. In order to understand the damage caused by the earthquake, and find a solution to mitigate the liquefaction-induced damage in Sapporo city, a preliminary investigation of the 2018 Hokkaido Iburi-tobu earthquake was conducted from 18 to 20 September 2018.
The damages to the houses at Satozuka town and Utsukushigaoka town in Sapporo city are focused on. The damage at Satozuka was so enormous that the residents could not continue to live in their houses. Although the inclination of houses can be seen by visual inspection at Satozuka, there were few houses where the inclination can be judged visually at Utsukushigaoka. Therefore we did a field survey of inclined houses by using a digital angle meter at Utsukushigaoka.
The inclination of 57 houses at Utsukushigaoka was measured, and the maximum value and direction of inclination are shown on the map. The houses located at the reclaimed land of the former river and former valley plain were inclined. Therefore, the old terrain greatly affected to the inclination of houses. These liquefaction-induced damage occurred in the same area where liquefaction occurred during the 2003 Tokachi-oki earthquake.
KeywordsThe 2018 Hokkaido Iburi-tobu earthquake Liquefaction Damage to houses Inclination of house
A big earthquake occurred and hit Hokkaido, Japan on September 6th, 2018. Many serious damages such as landslide, liquefaction and collapse of houses occurred by this earthquake. Liquefaction caused road deformation and inclination of houses in Sapporo city, Hokkaido. Many roads were inaccessible, and operation of emergency vehicle was affected by the ground deformation directly after the event. Inclination of houses also caused health problems for the residents. Therefore, these damages were serious problems in Sapporo city, Hokkaido.
We conducted field surveys such as measurement of inclination and interview to the residents of 57 houses at Utsukushigaoka, Kiyota ward, Sapporo city in this research. The direction and angle of inclination of the houses are shown on the map, and the map is compared to the old topographical map and liquefaction history of past earthquakes. Then, we discuss the mechanism of inclination of houses by liquefaction.
Methodologies and findings
Outline of earthquake damage
(a) The Human damage caused by the earthquake. (b) The houses and buildings damage caused by the earthquake (Cabinet Office 2018)
The human damage (person)
The damage to houses and bildings (building)
Liquefaction occurred in some areas. Uplift and sinking of road and inclination of houses were caused by liquefaction in the part of southeastern Sapporo city. Enormous liquefaction-induced damage occurred in a wide area of Satozuka and Utsukushigaoka, Kiyota ward, Sapporo city. The present study focuses on the damage to houses induced by liquefaction.
Furthermore, all power plants in Hokkaido stopped, and a massive power outage of 2.95 million households occurred. The blackout was completely eliminated on October 4th. Water supply also stopped in Sapporo city and some towns. Water stop continued at Atsuma for more than 1 month.
Liquefaction in Kiyota ward, Sapporo city
The green portion in Fig. 4 indicates Utsukushigaoka 1 jo. There were many inclined houses due to liquefaction. The houses shown in Fig. 4-⑤ seems to suffer no damage at first glance, but inclination of houses occurred. Most of the residents continued to live at the inclined houses just after the earthquake, but many residents moved without being able to withstand the inclination of houses after around 1 month.
The red portion in Fig. 4 indicates Utsukushigaoka 3 jo. Many houses suffered inclination by liquefaction. The inclination of the house shown in Fig. 4-⑥ was the second largest inclination in Utsukushigaoka. The residents of this house moved soon after the earthquake. The surrounding ground of the house shown in Fig. 4-⑦ subsided, and there was a gap between the stairs and the ground. The inclined houses shown in Fig. 4-⑧ were inclined to the direction of each house. The right house was with the largest inclination in the Utsukushigaoka. The utility pole shown in this photo has settled about 1.8 m (Wakamatsu and Onoue 2018).
Although the inclination of houses can be seen by visual inspection at Satozuka, there were few houses where the inclination can be judged visually at Utsukushigaoka. Therefore we did a field survey of inclined houses by using a digital angle meter in Utsukushigaoka.
Investigation of inclination of houses by liquefaction
Overview of field survey
Utsukushigaoka, Kiyota ward, Sapporo city was selected as a target area in this research because the inclination of houses caused a serious health problems of the residents and the liquefaction also occurred in the past earthquake. The maximum JMA seismic intensity of Utsukushigaoka 1jo and 3jo was 5 + and the maximum horizontal acceleration at the strong motion station (K-NET HKD 182) closest to the Utsukushigaoka was 205.8 gal.
The field survey was conducted on September 19th and 20th, about 2 weeks after the earthquake. The survey was conducted by using a “Neoteck Digital Angle Meter” to measure the inclination of the four outer walls of each house.
Results of measurements
Inclination of houses (Utsukushigaoka 1jo, A to C)
Inclination of houses (Utsukushigaoka 1jo, D to G)
Hokkaido has frequently suffered damages induced by liquefaction, such as in the 1952 Tokachi-oki, the 1993 Kushiro-oki, the 2003 Tokachi-oki earthquakes. The enormous liquefaction damage caused by the 2003 Tokachi-oki earthquake in Sapporo city. The liquefaction in the 2018 Hokkaido Iburi-tobu earthquake is compared with that in the 2003 Tokachi-oki earthquake here.
The surveyed areas of this study was originally recessed areas that erodes mountains, plateaus and terrace, then the area was reclaimed for residential houses in 1965. Houses D to F and G were located at the former flood and valley plains, houses A to C and H to J were located at the former bottom of valley plains. It was revealed that the inclination damage of houses due to liquefaction is greatly affected by the old topography. According to a survey of the Civil Engineering Research Institute for Cold Region, it is known that the survey target site is about 3 m of filled volcanic ash and the groundwater level is about 1 m. The groundwater is very shallow and it is considered that the ground is a high possibility of liquefaction.
The present study introduced the damage to houses induced by liquefaction in the 2018 Hokkaido Iburi-tobu earthquake. The damages to the houses at Satozuka and Utsukushigaoka in Sapporo city are focused. The damage at Satozuka was so serious that the residents could not continue to live there. Although the inclination of houses can be seen by visual inspection at Satozuka, there were few houses where the inclination can be judged visually at Utsukushigaoka. Terefore we did a field survey of inclined houses by using a digital angle meter in Utsukushigaoka.
The inclination of 57 houses at Utsukushigaoka, Sapporo city was measured, and the maximum value and inclination direction were shown on the map. The houses located at the reclaimed land of the former river and former valley plain were inclined. Therefore, the old terrain greatly affected the inclination of houses. These liquefactions induced damage occurred at the same area of liquefaction occurred in the 2003 Tokachi-oki earthquake.
Health problems may occurr at houses with an inclination of 0.6 degree or more, and about 53% of the surveyed houses exceeded this. Survey of inclination of houses was conducted again 1 month after the earthquake. Inclination of houses increased more than 1.8 degree in some cases by the aftershocks. The residents found living there difficult and most of residents decided to move. Therefore, it is considered that countermeasures to liquefaction of detached houses are necessary because liquefaction induced damage to houses has a great influence on the health of residents. Since liquefaction measures for houses are not widely used at present, in areas where there is a high risk of liquefaction, it is necessary to take measures to reduce such inclination damage.
This work was supported by JSPS KAKENHI Grant Numbers 18H01677 and 18 J11630. All members of the reconnaissance team are much indebted and thankful to the residents of Kiyota ward, Sapporo city, for their kind supports to the survey activities in the stricken areas. Lastly all the members would like to express hereby their sympathy to the people affected by the devastating earthquake.
YS, MM, MY and KM participated in the field investigation. YS and MM drafted the manuscript. All authors have read and approved the final manuscript.
This work was financially supported by JSPS KAKENHI Grant Numbers 18H01677 and 18 J11630.
The authors declare that they have no competing interests.
- Cabinet Office (2018), About the damage situation to affect the 2018 Hokkaido Iburi-tobu earthquake, Japan, http://www.bousai.go.jp/updates/h30jishin_hokkaido/pdf/310128_jishin_hokkaido.pdf (last visit: 30 Jan. 2019).Google Scholar
- Japan Meteorological Agency. 2018. About the “the 2018 Hokkaido Iburi-tobu earthquake, Japan”. Vol. 6 https://www.jma.go.jp/jma/press/1809/07c/kaisetsu201809071600.pdf (last visit: 30 Jan. 2019.Google Scholar
- Kohiyama, M., C. Keino, and T. Sonabe. 2012. Questionnaire survey on health disturbance of residents in mihama ward, Chiba City who suffered housing damage due to liquefaction. Journal of Social Safety Science (17): p. 1. http://isss.jp.net/isss-site/wp-content/uploads/2013/08/2012-016_cd.pdf. (last visit: 26 Nov. 2018).
- The Japanese Geotechnical Society (2018), Recconnaissance team of geotechnical disasters in the 2018 Hokkaido Iburi-tobu earthquake, liquefaction damage due to the 2018 Hokkaido Iburi-tobu earthquake, Japan, https://www.jiban.or.jp/wp-content/uploads/2018/10/nishimura_watabe_20181002.pdf (last visit: 26 Nov. 2018).Google Scholar
- Wakamatsu, K., Onoue, A. (2018), Geotechnical disasters in Utsukushigaoka, Kiyota ward, Sapporo City in the 2018 Hokkaido Iburi-tobu Earthquak, http://www.koa-kaihatsu.co.jp/wp-content/uploads/2018/09/utsukushigaoka_kiyota_report%E8%88%88%E4%BA%9CHP.pdf (last visit: 26 Nov. 2018).Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.