On April 18, 2025, Oita Prefecture experienced a series of earthquakes that have raised concerns among local residents and officials. Starting at around 8:57 AM, a significant earthquake with a magnitude of 3.7 was registered, marking the first time in approximately a year that seismic activity of this intensity has been recorded in the central region of Oita.
The earthquake, which struck at a depth of about 10 kilometers, registered a maximum seismic intensity of 3 in Beppu City. Tremors were also felt in other areas, including Oita City, Yufu City, and Hiji Town, where seismic intensities of 2 and 1 were observed. According to the Meteorological Agency, there is no concern regarding a tsunami following this event.
In total, six earthquakes were reported in Oita Prefecture by 9 AM on the same day, all originating from the central part of the region. The Oita Local Meteorological Observatory noted that these earthquakes occurred at nearly the same location and that similar seismic events have happened in the past. Importantly, they do not consider this series of tremors to be precursors to a larger earthquake. "We want people to continue preparing for earthquakes on a regular basis," an official stated.
Just before noon, another earthquake was recorded at 12:53 PM, which had a lesser magnitude of 2.3 and a maximum seismic intensity of 1, again centered in the central part of Oita Prefecture. This minor quake was also confirmed to pose no tsunami threat.
The seismic activity on April 18 is particularly noteworthy due to its location near the Median Tectonic Line Fault Zone, a region known for its active fault lines. This area has seen increased seismic activity since the Kumamoto earthquake in 2016, which triggered a series of aftershocks and related quakes in Oita Prefecture. The last earthquake that reached a seismic intensity of 3 or higher in this area occurred back in May 2024.
According to the rapid report analysis by the National Research Institute for Earth Science and Disaster Resilience, the earthquake on April 18 is classified as a normal fault type with a compressive axis oriented north-south. The epicenter is believed to be near the Imi-Asamigawa Fault, part of the Yabakei-Yufuin area within the Median Tectonic Line Fault Zone.
The government’s Headquarters for Earthquake Research Promotion has released statistics indicating that the probability of a large-scale earthquake exceeding magnitude 7 occurring within the next 30 years in this region is quite low. Specifically, the Median Tectonic Line Fault Zone and the Hiji-Se Fault Zone have probabilities close to 0%, while the Mt. Yufu-Tsurumidake Fault Zone has a slightly higher probability of 0.004%.
Despite the presence of active volcanoes such as Mt. Tsurumi and Mt. Garan in Beppu City, experts believe that the recent earthquakes are unlikely to be related to volcanic activity due to their distance from the mountains and the depth of the seismic events. The earthquakes in this region are often shallow, and even minor quakes can result in noticeable tremors near the epicenter, necessitating continued vigilance among residents.
As Oita Prefecture continues to monitor seismic activity, local authorities are urging residents to remain prepared and aware of earthquake safety measures. The recent events serve as a reminder of the region's geological volatility and the importance of preparedness in the face of natural disasters.
