Kumamoto Earthquakes (熊本地震)

Kumamoto, a place that I consider to be my second home, has been hit by a barrage of earthquakes. It is one thing to go through one major earthquake, but Kumamoto was hit by four earthquakes measuring higher than magnitude 5.5 over two days. Just over a week on, and the frequency of earthquakes has diminished. There has been over 1000 earthquakes that were measurable in the  Japanese shindo (shaking) scale (1-7) since the first one on the evening of April 14th. Both the the first earthquake and the major magnitude 7 earthquake had a peak shindo rating of 7. Only a handful of earthquakes in Japan have reached this quantification since they started using it in 1923.

I have to admit, as someone who has spent a lot of time studying geophysics, including earthquake seismology, I did want to experience what a big earthquake is like. After the first one, I found out. It was like being in the box of a mosh pit. It feels like people are pushing you around in all different directions. We were on the second floor of an apartment, which may have amplified this kind of feeling. I’ll admit, it was kind of exciting. After the second big earthquake (about half an hour later), I was kind of thinking that I could do without feeling more earthquakes. By the time that one came, we were outdoors in an open parking lot.

The first earthquake registered as a magnitude 6.5 according to the Japanese Meteorological Agency. It was a pretty strong jolt that basically knocked over anything that wasn’t bolted to the ground. Note that the USGS rated it a magnitude 6.2; the JMA uses a different calculation method for determining magnitude, apparently (though the USGS epicenter is over 10 km from where the actual earthquake epicenter was, so there may be some model dependent issues as well). The apartment I was staying at was around 12 km from the first earthquake epicenter. Considering how shallow it was (<10 km depth), the earthquake produced vigorous shaking over the entire city.

The first time I came to Kumamoto, I was interested to know about the possibility of a large earthquake. It was only two years removed from the major Touhoku Earthquake. I knew, considering its location in western Kyushu, that Kumamoto was unlikely to be threatened by a megathrust earthquake. There wasn’t much of a record of damaging earthquakes in the area in the historic record, as far as I could determine in my searches. The USGS database (which goes back to 1973) shows that the largest earthquake in recent times in the Kumamoto city region was a magnitude 5.0 in June 2000:

A magnitude 5.0 might produce quite a bit of shaking, but the amount of damage would have been quite limited. The most significant disaster in the history of this region was the 1792 Mt Unzen landslide/eruption (it is not certain if it was a volcanic eruption). This produced a tsunami that killed thousands of people in Kumamoto. In my search for this article, I found out about an earthquake in 1889, with an estimated magnitude of 6.3. This quake was attributed to activity at the likely dormant volcano, Mt Kinpo, located west of Kumamoto city. That earthquake killed 20 people. Obviously my original search of past earthquakes was not so thorough. There were actually some pictures taken after the 1889 earthquake, and it is not altogether dissimilar to the damage caused by the magnitude 7.3 earthquake.

Compare that to after the second, larger magnitude 7.3 earthquake:

It should be noted that the magnitude 6+ earthquakes that happened the day before the 7.3 did minimal damage to the castle. Mt Kinpo is closer to Kumamoto Castle than the epicenter of the recent earthquakes, which were just to the east of Kumamoto city in Mashiki Town. I would suspect that is the reason the damage looks the same.

I have to say, I feel pretty lucky right now. The area I stayed in was relatively undamaged, compared to Mashiki, where there were a lot of buildings damaged. Some of the older parts of the town near where I stayed were also well damaged. The death toll also has remained below 50 people. There are two reasons why this is true. First, the building regulations of Japan were improved substantially after the Great Hanshin Earthquake in 1995, where thousands died. Second was the fact that the smaller (but still significant) earthquakes happened a day before the main shock. A lot of people were camped out in cars, tents and evacuation areas when the main 7.3 earthquake happened.

I used to live in Victoria, British Columbia, where I did my masters degree. As part of that, I was surrounded by people who’s very job was to make sure that people in the city were aware of the risk of earthquakes and be prepared. Despite that, I have to admit that I was woefully unprepared for an earthquake. I did not have a supply of fresh water or food in case of a disaster. Even after the first set of earthquakes, I did not get a stock of supplies. We did not have running water for the majority of last week, so this is not something that I am kidding about. Again, I feel pretty lucky because the area of our city was not damaged a lot, and the food stores opened the day after the big earthquake, and had ample supplies. We were able to get water from my fiancee’s nearby hospital, and were able to fill our bathtub with water during a brief interval when the water came back on during Tuesday. The water was probably not suitable for drinking, but it was fine for the toilet.

Tomorrow, I fly off to Germany to start a new position there. It is both a relief and a sad time for me to be leaving Kumamoto. I hope that the area recovers quickly, and we can enjoy the hospitality of the people here, and the wonderful sites to see, like Kumamoto castle and Mt Aso.