Introduction
The Nankai Trough is a deep-sea trench located off the southern coast of Japan. It is where the Philippine Sea Plate moves beneath the Eurasian Plate, a process called subduction. This movement can cause great earthquakes and tsunamis. The Japan Earthquake Research Committee (JERC) has warned that there is a 75% to 82% chance of a major earthquake along the Nankai Trough within the next 30 years. This risk affects not only Japan but also regions like Hong Kong, which can experience indirect impacts. Understanding the geological context helps travelers plan and stay safe.
Geological Context of the Nankai Trough
The Nankai Trough stretches about 700 km from Suruga Bay to Hyuga-nada. The Philippine Sea Plate moves under the Eurasian Plate at a rate of 5 cm per year. This movement builds up stress, which can suddenly release, causing earthquakes. Historical records show that great earthquakes of magnitude 8 or higher have occurred every 100 to 200 years. The largest recorded earthquake was the M8.6 Hoei earthquake in 1707, which caused a massive tsunami and over 5,000 deaths. Tsunami sediment studies suggest that similar tsunamis may occur every 300 to 600 years.
Potential Impact on Hong Kong
Hong Kong is about 600 km from the Nankai Trough. While it is far, Hong Kong can still experience slight sea level changes from tsunamis. For example, the 2011 M9.0 earthquake at the Japan Trench caused a 0.2 m sea level change in Hong Kong. If a great earthquake occurs along the Nankai Trough, tsunami waves could reach Hong Kong’s southeastern waters in about 6 hours and the northwestern part in 1 to 2 hours. A shallow M9.1 earthquake could cause significant tsunami waves in some coastal areas, while an M8.0 earthquake would likely cause only slight water level changes.
Disaster Preparedness and Travel Safety
The Hong Kong Observatory (HKO) issues Tsunami Warnings and Tsunami Information Bulletins to alert the public. A Tsunami Warning is issued if a significant tsunami is expected to reach Hong Kong within 3 hours. A Tsunami Information Bulletin is issued if a tsunami may reach Hong Kong but is not expected to be significant, or if a significant tsunami is expected to arrive more than 3 hours later. Travelers should stay informed and follow local government warnings. It is important to have emergency plans, including evacuation routes and communication strategies.
Historical Earthquakes and Tsunamis
Great earthquakes have occurred along the Nankai Trough for over 1,400 years. The Hakuho (Tenmu) earthquake in 684 was one of the earliest recorded. Since then, great earthquakes have occurred every 100 to 200 years. The M8.6 Hoei earthquake in 1707 caused a massive tsunami and over 5,000 deaths. Tsunami sediment studies show that similar tsunamis may occur every 300 to 600 years. These historical events highlight the need for preparedness and understanding of seismic risks.
Tsunami Simulations and Predictions
Tsunami simulations for M9.0-9.1 earthquakes along the Nankai Trough help predict potential impacts. The amplitude of tsunami waves reaching Hong Kong depends on factors like the earthquake rupture process, geological structures, and seabed topography. A shallow M9.1 earthquake could cause significant tsunami waves in some coastal areas, while an M8.0 earthquake would likely cause only slight water level changes. Accurate modeling and simulations are crucial for disaster prevention.
Traveler’s Guide to Seismic Risks
Travelers to Japan should stay informed about seismic risks and potential travel disruptions. Local authorities provide information and warnings, which should be heeded. Travelers should have emergency plans, including evacuation routes and communication strategies. Resources like the Hong Kong Observatory and travel insurance can help stay updated on seismic activity and tsunami warnings. Travel insurance can also provide coverage for cancellations and emergencies.
