USJI Voice Vol.17
Infrastructure for Disaster Resilience – Some Lessons from the Kumamoto Earthquake
1. Kumamoto Earthquake
A strong earthquake hit Kumamoto on 14th April 2016, and it was followed on the 16th by an even stronger main shock of magnitude 7.3 according to the Japan Meteorological Agency (JMA). These earthquakes were accompanied by an unprecedented number of aftershocks, which hindered activities to restore the damaged area and support the people. In the aftermath of huge earthquakes, it is essential for society to recover as quickly as possible. Efficient recovery requires infrastructure to enable people and supplies to be sent into the affected areas.
This short report outlines the damage caused to infrastructure by the 2016 Kumamoto Earthquake and lessons to be learned.
2. Infrastructure Networks
After the Kumamoto Earthquake, the number of evacuees exceeded 180,000, which is very large compared to the number of casualties and missing persons which totaled 50. This indicates the importance of support for recovery. Such support comes mainly from outside the affected area and thus requires transportation networks, but the networks connecting Kumamoto to major cities in Kyushu, such as the Kyushu Expressway and the national routes near the Aso area, were damaged over a wide area.
Alternative routes should have been constructed in preparation for such disasters. In Kyushu, however, earthquakes did not have a high priority before this one. Can we prepare for unexpected disasters? In fact, earlier simulations of other disasters such as the volcanic eruption of Mt. Aso revealed the vulnerability of the link between Kumamoto and Oita. Even if we do not have accurate information about potential severe disasters, it is possible to prepare for them.
3. Individual Structures
Many bridges were damaged by the Kumamoto Earthquake, but most of them did not suffer critical damage to the piers. This was thanks to efforts in the last two decades since the 1995 Kobe Earthquake. After that earthquake, design codes in Japan were updated several times and structures were designed considering large design forces. Old bridges that had been constructed before the revision of the design codes have been retrofitted in the last two decades to satisfy the new requirements. Nevertheless, some important bridges suffered severe damage and could not continue to be used. It is costly to build structures to resist severe earthquakes without damage. Should we raise the seismic design force even higher?
Several damaged bridges in the Kumamoto Earthquake suggest an alternative approach. The Kiyamagawa Bridge of the Kyushu Expressway and the Kuwatsuru Bridge on prefectural route No.28, for example, were damaged but did not collapse. Devices to constrain the displacement of the girder guided these bridges to a mode of less severe damage, and so their recovery will require less time and resources. In the case of a very strong earthquake that will inevitably cause damage, if structures avoid falling into a catastrophic situation, it helps contribute to the resilience of society. This concept of seismic performance is called “anti-catastrophe”, and is expected to be implemented in seismic design codes of various infrastructures.
4. Social Resources
The time required for the Shinkansen to resume service after strong earthquakes was 81 days after the 1995 Kobe Earthquake, 66 days after the 2004 Chuetsu Earthquake, 49 days after the 2011 Great East Japan Earthquake, and 13 days after the Kumamoto Earthquake. After the Kobe Earthquake, the Hanshin Expressway (Route 7 Kita-Kobe Line) resumed service 39 days later. After the Chuetsu Earthquake, it took 13 days. After the Great East Japan Earthquake, the Tohoku Expressway resumed service for the public 13 days later. After the Kumamoto Earthquake, the Kyushu Expressway resumed service 13 days after the main shock. Although these numbers cannot be simply compared because the damage differed for the different events, it would seem that the organizational capability to restore infrastructure services has improved.
The scale of resources is also important. The Ministry of Land, Infrastructure, Transportation, and Tourism (MLIT) dispatched 8,134 (person-days) professional personnel, called Technical Emergency Control (TEC) Force, during the first month after the earthquake. The availability of a large number of skilled and responsible staff to provide such technical and professional support is essential.
The same is true for resources such as engineers and heavy machinery of private companies. After the 2011 Great East Japan Earthquake, Operation “Comb” succeeded in restoring access to the severely damaged coastal areas in a couple of days. This was possible because 52 teams of construction companies were formed immediately after the earthquake and cooperated in the recovery work. It could have failed if it had not been for the large number of expert construction companies.
These resources are not infrastructure itself, but they are essential factors for the resilience of infrastructure. From the viewpoint of social resilience, it is essential to keep these resources of society ready for the next major disaster.
Severe natural disasters are destructive and it is impossible to perfectly prepare for them. Therefore, besides minimizing the damage, we also need to think about the recovery after the event. Social resilience is a very important and urgent issue for Japan, which is prone to various disasters, including the predicted Nankai-Tonankai Earthquake.
The 2016 Kumamoto Earthquake was devastating, but there are lessons we can learn from this experience. This short report discussed some aspects associated with infrastructure, organization skill, and design codes. I hope it will help readers to gain an understanding of the disaster resilience required by society.