Many places in Japan prepare for the earthquake, Kishida Fumio emergency cancellation of overseas visit plans, Japan's future one What is the likelihood of a major earthquake this week? What is the expected impact?

The Nanhai Trough earthquake, also known as the "Nanhai トラフ earthquake" in Japan, is a looming natural disaster that has long been considered a "sword of Damocles" hanging over western Japan. This region, like China's Anning River fault zone, has a history of devastating earthquakes, and experts believe that the next seismic event is drawing closer. Understanding this earthquake requires an exploration of both its historical context and the potential for foreshocks that could precede it.

Historically, the Nanhai Trough region has been the site of significant seismic activity. Similar to other tectonic plate boundaries, this region is prone to massive earthquakes due to the constant movement and pressure between the Earth's plates. These movements can result in sudden and violent shifts, leading to devastating earthquakes. The Nanhai Trough, in particular, is a subduction zone where one tectonic plate is forced beneath another, creating the conditions for a megathrust earthquake.

One of the key concerns with such megathrust earthquakes is the possibility of foreshocks. Foreshocks are smaller earthquakes that occur before a larger seismic event, often acting as a precursor to the main shock. For instance, the 2011 Tōhoku earthquake in Japan, which resulted in a catastrophic tsunami, was preceded by a magnitude 7.3 foreshock just one day earlier. Similarly, the 1960 Valdivia earthquake in Chile, the largest earthquake ever recorded at a magnitude of 9.5, was preceded by a series of strong foreshocks, including magnitudes of 8.1, 7.1, 6.8, and 7.8.

The foreshock mechanism for such large earthquakes is not fully understood. However, it is thought to be related to the gradual release of stress along the fault line, which eventually leads to a massive slip or collapse. In this context, foreshocks can be seen as the first signs of a fault beginning to rupture, with smaller blocks of rock breaking away before the main event. This process can provide crucial warnings, allowing for early detection and the possibility of issuing alerts.

In Japan, the Meteorological Agency closely monitors seismic activity in the Nanhai Trough region, particularly focusing on thrust-type strong earthquakes with magnitudes greater than 6.8. When such an earthquake occurs, the agency often issues a large earthquake alert, indicating that the probability of a major earthquake has increased. For example, after a magnitude 7 earthquake in the region, the probability of a significant earthquake in the Nanhai Trough rises from around 0.1% to 0.5%. While this increase may seem small, it is a significant jump that prompts the government to take precautionary measures, such as advising the public on disaster preparedness and opening shelters.

If a magnitude 8 earthquake were to occur in the area, the Japan Meteorological Agency might issue an even more severe alert, indicating that a major earthquake is highly likely. This level of alert would necessitate immediate action, including the need for residents to seek shelter. Historically, the Nanhai Trough region has experienced multiple significant earthquakes within a short time frame, such as the two magnitude 8 or higher earthquakes that occurred within 48 hours of each other in the past. This historical precedent underscores the importance of vigilance and preparedness.

Recently, the Meteorological Agency issued a large earthquake notice for the Nanhai Trough region following a magnitude 7.1 earthquake off the coast of Miyazaki on August 8. This earthquake, known as the Himotan Beach earthquake, occurred at the western end of the area defined as the source of the Nanhai Trough's massive earthquakes. Although the epicenter was somewhat distant from the typical locations of past Nanhai Trough earthquakes, it reignited concerns about the potential for a larger seismic event in the region.

While the probability of a massive earthquake in the Nanhai Trough remains low, at around 0.5%, the possibility cannot be ignored. The energy buildup in the region suggests that a significant earthquake could occur before 2050, although the exact timing remains uncertain. The recent Miyazaki earthquake has brought the Nanhai Trough back into focus, increasing public anxiety and prompting more disaster preparedness efforts. However, it is crucial to remember that earthquakes often strike when least expected, and continued vigilance is necessary to mitigate the potential impact of such a devastating event.