Kumamoto

A Lesson from Japan’s Latest Destructive Earthquake on How to Strengthen Older Schools (and Buildings)

by Peter Yanev

Yanev Associates and Kuramoto Earthquake Investigation Team Technical Leader

Once again, I find myself in Japan immediately after a big earthquake. I left California the day after a Magnitude (M) 7.0 earthquake hit Japan’s Kyushu Island to join several colleagues in investigating the effects of the earthquake. Critically, I also came to Japan to learn from the successes of Japanese engineers. Older school strengthening programs are one of the great successes of Japan. Our earthquake investigation team did not review the overall performance of schools in the affected area of the earthquake, but we were able to observe the performance of several schools in the area of the strongest shaking, including the Mashiki area.

The Town of Mashiki straddles the Futagawa Fault, where the some of the largest fault displacements in the earthquake were found – nearly 2m (6 ft.) of horizontal displacement and about 0.7m (2+ ft.) of vertical displacement. The town and its region lie along a river, and its buildings, mostly houses are built on river alluvium and along the hills on both sides. The houses in the Mashiki area experienced the worst damage that I have ever observed to wood-frame buildings – that includes about 120 earthquakes around the world.

We observed that, generally, there was no visible structural damage to the schools in the area. In the first day of investigations, we looked briefly at two schools and investigated one in detail, the Mashiki Tsumori Elementary School which is very, very close to the fault that ruptured the ground and caused the earthquake. The school is located in the middle of some of the worst damage caused by the earthquake. The area experienced some of the strongest, if not the strongest, shaking in this major earthquake. The performance of the school in the earthquake is a great lesson in good engineering and good social risk management.

We visited the school on April 19, 2015, five days after the earthquake. We noted that there was no tag on the building(s) indicating that the school had been officially inspected for safety and restart of operation. We poked around a few minutes and while taking some exterior photographs, we were greeted by some of the teaching and maintenance staff. They were curious why we were there and what were we doing. When we explained, and within a few minutes, we were conducting an unofficial damage and safety assessment of the school with the school principal and several of the teaching staff.  It was remarkable that the school had not been officially inspected, especially given the results of our impromptu and much appreciated investigation.

The investigation took perhaps 30 minutes. We visited all of the several relatively small buildings, many of the classrooms and other rooms of the school, and its sport auditorium.

Of course, the reason we stopped by in the first place was that it was obvious to me that the school was older and had been strengthened (retrofitted) for earthquakes sometime after it was originally constructed. Such strengthening of schools started sometime after the 1978 Magnitude 7.4 Sendai (Miyagi-Ken-oki), Northern Japan earthquake. That was my first earthquake investigation in Japan, as well as my first visit to Japan and I saw firsthand a number of collapsed school buildings. The earthquake damaged extensively many schools and university buildings in the Senday area; a few buildings collapsed. Since then, I have investigated many earthquakes in Japan and have visited Japan 40 to 50 times. I also opened an office in Tokyo, Japan for my former company, EQE International shortly after the 1975 Kobe earthquakes and worked on many earthquake-engineering projects throughout the country, including projects on some of Japan’s nuclear power plants following the Magnitude 8.8 earthquake and tsunami of 2011.

Figure 4 above, shows one of the most common details that are used for the strengthening of schools throughout the world. It involves inserting new, solid and well reinforced concrete walls (called shear-walls) between existing columns in order to strengthen the buildings. These walls can be added to the exterior, as in this school, or to the interior (which tends to be less architecturally disruptive but also more expensive). Working with the World Bank, for example, we have managed the strengthening of over 1,000 such buildings (mostly schools and health-care buildings) in the Istanbul, Turkey area since 2005, using this technique.

Figure 6. Views of collapsed buildings around the school. The bottom photograph is from inside a  classroom, looking at a collapsed building across the river (also shown in the left photo above)

 

With the principal and some of his staff we walked throughout the school looking for damage. Some of this damage, and the lack of it, and some of the interiors and exteriors of the buildings are shown in the pictures below. The Principal showed me some of the damage that was of concern to him. It turned out to be superficial damage that has no effect on the strength of the post-earthquake buildings and the safety of the students and staff. The damage included minor cracking, especially around some of the so-called seismic joints that separate adjacent buildings and are expected to be lightly damaged (he, of course, did not know that), fallen pictures and books and other minor furnishings, a bit of ground settlement in the yards around the school, a few fallen ceiling tiles (in the gym) and other light fixtures (yes, they can injure people), the fallen temple monuments surrounding a small shrine on the school grounds (which could have hurt badly someone standing next to them), etc.

It was remarkable, once again, how little was damaged, given the size and the strength of the earthquake. The damage, or really the lack of it, shows how well we understand the effects of earthquakes on school buildings and how well we can protect our kids and their teachers. It also shows that the strengthening of our older schools (those designed to outdated codes, written before the lessons of so many recent earthquakes) reduces dramatically the risk to their occupants. This has now proven to be the case in all recent major earthquakes in Japan, as well as in California and Chile, for example, where society has provided the needed funding to do the engineering and construction work. I saw similar performance in many old but strengthened schools in Chile in their M9.0 2010 earthquake and in Japan in the M8.8 2011 earthquake that caused the major tsunami and the destruction of some of the Fukushima Nuclear Plants (which was actually caused by the flooding as a result of the lack of adequately high tsunami walls). In fact, one of the most memorable sights of that earthquake was an old school near Nishinomaki that had been strengthened for earthquakes. The structure of the school was barely damaged, even after it was shaken by a Magnitude 9 earthquake for several minutes and was then hit by the great tsunami plus a localized fire, likely caused by leaking gas. So, the performance of the Mashiki Elementary School was not surprising to me. I expect that of those schools in Japan, and elsewhere, that have been strengthened. I just hope that we continue fixing schools, and other public and private buildings and infrastructure, before their respective and expected earthquakes occur.

Figure 8 Additional photos of the interior and the exterior of the elementary school.

 

We have spent the morning writing the report and choosing photographs.  Here are the first about Mashiki Town.

On Monday, 4/18, we drove from Fukuoka to Mashiki Town, where some of the heaviest damage took place.  Mashiki Town is located in a valley east of Kumamoto.  We drove into the valley from the Kumamoto Airport and entered Mashiki through Kami Upper Valley Village.  The damage was severe.  Here the fault ruptured the surface and the ground motion was about 1.4 g.

Here is the fault at the east end of the valley.

More tomorrow: Pater Yanev’s report on Tsumori Elementary School and Koji Okumura’s report on the geology and the shaking.

Maybe the most interesting part of the day was our visit to the Tsumori Elementary school in Mashiki Town.  We stopped there because amidst severe damage to homes in that area, the school remained remarkably intact, even though it was built before the new 1981 seismic code. The school principal, Satoh Kosuke, and his staff were busy cleaning the school, which, of course, was really messed up inside.

We were the first people to stop at the school, including government officials or earthquake experts, and the first people to help them understand the earthquake damage to the school and to answer questions, in general, about what was safe and what was not.

In our opinion, the implications for the USA, and other countries, are grave. For example, there are similarities about what could happen from a rupture of the Hayward Fault in the San Francisco East Bay area.  As one team member said, “There was way too much damage in modest homes which look like mine, in neighborhoods which look like mine, and near a fault just like the one near me.”

It was not only old buildings which were damaged.  There seems to have been a unique combination of strong ground motion and geotechnique effects, such as liquefaction and landslides. One team member remarked that after 120 earthquake investigations, this was the most residential damage that he had ever seen.

The faulting was much too complicated, much to sophisticated, and treacherous.  It seems that all the geologists have been outsmarted.  We strongly feel the limitations of our profession … but we must proceed to gain even better understanding.

Once again, Mother Nature, using earthquakes, has fooled the best scientific professionals with her power and variability.

We have a ways to go…