News Excerpt:

Following a recent 7.1-magnitude earthquake in southern Japan, the country's meteorological agency issued its first-ever "megaquake advisory."

What is a Megaquake?

• A megaquake, often referred to as an extreme earthquake, is an exceptionally rare geological event that registers at a large magnitude on the Richter scale, typically defined as having a magnitude of 7.0 or higher. 
• These formidable seismic occurrences are among the most powerful earthquakes, capable of causing catastrophic destruction over wide areas. 
• The sheer intensity of a megaquake can lead to significant loss of life, widespread infrastructure damage, and long-lasting disruptions to communities and ecosystems.

What is the Nankai Trough?

• The Nankai Trough is an extensive underwater subduction zone, approximately 900 km in length, where the Eurasian Plate meets the Philippine Sea Plate. 
• The advisory indicates a heightened likelihood of strong shaking and potentially large tsunamis, specifically along the Nankai Trough, a significant subduction zone off Japan's southwest Pacific coast.

• The process of subduction,where the Philippine Sea Plate is forced beneath the Eurasian Plate, builds up tectonic stress, which can eventually result in a "megaquake." 
• The megaquakes are significant seismic events with magnitudes greater than 8.
• Historically, the Nankai Trough has been the source of large earthquakes occurring approximately every 100 to 150 years. 
• These earthquakes often occur in pairs, with the second event typically happening within two years of the first.
• The last recorded pair of such earthquakes occurred in 1944 and 1946.

Recent Earthquake and Concerns:

• The recent 7.1-magnitude earthquake, which struck near the Nankai Trough, has raised concerns among experts.
• There is apprehension that this event could be a precursor to a more devastating tremor along the trough.
• According to Japan's Earthquake Research Committee, there is a roughly 70% probability that a magnitude 8-9 megaquake could strike along the Nankai Trough within the next 30 years.
• In case of such an event it could have widespread effects, sending tremors from central Shizuoka to southwestern Miyazaki.
• Tsunami waves as high as 98 feet could reach Japan's Pacific coasts within minutes.

Potential Impact of a Megaquake:

• A major earthquake along the Nankai Trough could have catastrophic consequences for Japan.
•  A 2013 government report estimated that such a disaster could affect an area covering about a third of the country, where nearly half of Japan's population resides. 
• The economic damage could exceed $1.50 trillion, representing more than a third of Japan's annual gross domestic product.

Earthquakes Prediction:

• Currently, the precise prediction of earthquakes remains impossible. 
• Accurate predictions would require a clear precursory signal from within the Earth, a signal that is detectable only before large earthquakes and not during minor seismic movements. As of now, no equipment exists to identify such signals reliably.
• The advisory issued by Japan's meteorological agency serves as a warning rather than a prediction.
• It encourages residents to prepare by reviewing evacuation routes and considering potential future warnings.