On August 8, 2024, Japan's Meteorological Agency (JMA) made an extraordinary announcement: the issuance of its first-ever alert regarding a potential megaquake in the Nankai Trough. This alert follows a significant seismic event, a magnitude 7.1 earthquake that struck off the coast of Kyushu earlier in the day. The agency's action reflects an elevated level of seismic risk, though it does not guarantee an imminent earthquake within a specified timeframe. The alert is set to remain in effect for one week, with a cautionary note that vigilance should be maintained beyond this period.
The JMA’s alert is part of a two-tiered system for earthquake notifications. The lower-level alert, issued on Thursday, advises the populace to prepare for possible evacuation scenarios. At this stage, no mandatory evacuations are enforced. In contrast, a higher-level warning would necessitate more immediate evacuation efforts and heightened awareness for those unable to evacuate swiftly. The expert committee of the weather agency will continue to evaluate the situation and adjust the alert level based on ongoing seismic conditions and the magnitude of subsequent tremors.
Historically, the Nankai Trough, a major subduction zone stretching from Suruga Bay to offshore Hyuganada, has been prone to large earthquakes approximately every century. The most recent significant quake occurred on December 21, 1946, registering between 8.1 and 8.4 on the moment magnitude scale. While such quakes are infrequent, their devastating potential necessitates robust preparedness measures. The JMA's alert signifies an increased likelihood of a major quake, prompting a reassessment of seismic risks in the region.
The implications of a substantial earthquake in the Nankai Trough are severe. Intense shaking is anticipated to affect a broad area from the Kanto region to Kyushu, with high tsunami waves likely impacting the Pacific coast from Kanto to Okinawa. For instance, a theoretical quake with a magnitude of 9.0 could cause shaking in the Kanto region comparable to the 2011 Great East Japan Earthquake. The potential for widespread destruction underscores the urgency of preparedness measures.
In light of the alert, Central Japan Railways, which operates the high-speed bullet train line connecting Tokyo and Osaka, has taken precautionary actions. Trains between Mishima and Mikawa-Anjo stations are being operated at reduced speeds, leading to delays of at least ten minutes. This proactive measure aims to mitigate the impact of potential aftershocks and ensure passenger safety.
The government’s damage assessments, published in 2012, reveal that a megaquake in the Nankai Trough could lead to up to 224,000 fatalities. However, effective evacuation procedures immediately following the earthquake could reduce this number by approximately 80%. Such statistics emphasize the critical importance of preparedness and the implementation of evacuation strategies to save lives in the event of a major seismic event.
The JMA's alert and subsequent precautionary measures underscore the evolving understanding of earthquake risks in Japan. The increased seismic activity observed, coupled with the alert, highlights the need for continued vigilance and comprehensive disaster preparedness strategies to mitigate the impact of future megaquakes.
