March 11, 2011, is a well-known date for everyone, except for those who were too young or not yet born at the time, as it marks the occurrence of the Great East Japan Earthquake. However, many people may not be aware that exactly one month later, on April 11, a major aftershock originating from Tabito-machi occurred, with a seismic intensity of around 6- (lower) and a magnitude of 7.0 (Fukushima Hamadori earthquake). The fault that I visited this time was caused by the aftershock.
The Itozawa fault can be seen near small villages in the mountains area. You will pass through a narrow road for about 5 minutes before arriving. There is no parking lot at the place where the fault is located, but a parking for visitors is provided in front of a house a little further back.
After parking my car and putting on my boots, a resident of the house approached and talked to me. When I told them that I wanted to see the fault, they handed me a leaflet (created by the Tabito Regional Development Council) with information about the Itozawa Fault. They also showed me where to look. Following their directions, I headed towards the area near the road I had just passed.
There is an information board near the fault, and a ginkgo trees was planted to convey the appearance of the fault to future generations. At the right end of the photo, the part that looks like a step extending from the front to the back is the fault.
It can be quite difficult to imagine, but is it possible that a place that was originally flat turned into a step like this after a single earthquake…? If I hadn’t been told, I might not have paid any attention to it, or I might have thought that the soil had been artificially piled up. By the way, the red and white striped pole have a height of about 2m.
道を挟んで反対側にも断層が続いていました。斜面を登っていきます。
The fault continued on the other side across the road. I walked up the slope.
上から見るとこんな感じ。さっきよりはっきりと断層であることがわかります。
Looking from above, it looks like this. It became clearer that it is indeed a fault, more than before.
When I entered the forest, the soil was exposed and I could clearly see the fault! Outside of the forest, it was not clearly because the fault was covered with grass, but inside, you can see even roots of the trees on the upper section.
When comparing it to the poles, you can see that the height of the fault is about 2 meters or more. The power of the earth is amazing that a single earthquake can shift the ground so much.
Once I backed to the parking, I noticed an arrow signboard towards the direction of the bamboo grove, so I headed there. After walked up along the ridge in the bamboo forest, and then…
！！すごい！きれいに断層が見えます。まるで山がスパッと切られてしまったかのよう…。
Wow! It’s incredible! The fault was clearly visible. It was as if the mountain has been cut through.
北側。さっき見た説明板などがある方向。
North side. In the direction where I previously saw the information boards.
South side. It was difficult to see clearly due to the bamboo, but the fault seemed to continue for quite a distance. According to the leaflet, the fault appeared for about 14km distance.
“By the Great East Japan Earthquake on March 11, 2011, the Japanese archipelago was heavily pulled towards the Pacific Ocean. In the Oshika Peninsula, closest to the epicenter, the electronic reference point moved 530 cm to the east, while in Tabito-machi, Iwaki City, it shifted 152 cm to the east. This crustal movement triggered the Hamadori Earthquake on April 11. The Itozawa Fault is normal fault type where the faulted part was pulled apart, causing the upper side of the fault slide down. Currently, most of the 14 km long fault has been restored, but the Itozawa fault has been preserved in its original state thanks to the kindness of the landowner. It is also designated as Iwaki City natural monument (Geological), as it was the first confirmed example of normal fault type earthquake fault in Japan and is scientifically valuable.”
It was my first time to observe an earthquake fault up close, and I was able to feel that the earth’s crust is active by seeing the crack in the mountains. It was a nice educational experience. See you.
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