The bustling metropolis of Tokyo, home to over 30 million people, faces a significant earthquake threat. Understanding past earthquakes, like the devastating 1855 Ansei Edo quake, is crucial for mitigating future disasters. This magnitude 7.0 earthquake, occurring as Japan opened to the world after centuries of isolation, claimed an estimated 10,000 lives and destroyed over 50,000 buildings.
The Ansei Edo earthquake wasn’t an isolated incident. It followed the massive 1854 Tokai and Nankai quakes, both measuring 8.4. These events highlight the region’s volatile seismic nature. The 1855 quake’s devastation is vividly depicted in woodblock prints showing Namazu, the mythical catfish believed to cause earthquakes.
Recently, University of Tokyo researchers unearthed a forgotten manuscript: the autobiography of Kabuki actor Nakamura Nakazo III. His account, Temae Miso, offers unique insights into the 1855 earthquake. Analysis of the original manuscript revealed key differences from later editions, providing clues about the quake’s depth.
Woodblock print of courtesans attacking Namazu, the mythical catfish blamed for earthquakes.
Nakamura described a short delay between the initial rumble (P-waves) and the violent shaking (S-waves). This short 5-10 second S-P interval suggests a shallow depth of roughly 20 kilometres, placing the rupture within the subducting Philippine Sea plate. This contradicts previous estimates of over 30 kilometres. Accurate depth estimation is vital for predicting ground shaking and potential damage in future quakes. Shallower quakes can cause significantly more surface damage.
The Japanese government predicts a 70% chance of another 1855-type earthquake striking Tokyo within 30 years, potentially killing 23,000 people. Understanding historical earthquakes like the 1855 Ansei Edo quake is crucial for developing effective mitigation strategies. Studying past seismic activity helps scientists understand patterns and potential future events, informing disaster preparedness and infrastructure development.
This research highlights the importance of interdisciplinary collaboration. Seismologists and historians from the University of Tokyo’s Historiographical Institute deciphered Nakamura’s cursive script and analysed historical records. This collaborative effort underscores the value of combining scientific and historical knowledge to understand past earthquakes and improve future preparedness. The findings corroborate existing research suggesting a shallow depth for the 1855 quake.
This interdisciplinary approach extends beyond Nakamura’s manuscript. Researchers are compiling a comprehensive database of historical seismic events, analysing materials like official reports, personal diaries, and visual records. Each source provides unique insights into past earthquake activity, helping researchers build a comprehensive understanding of seismic risk. This long-term perspective is invaluable for assessing future earthquake hazards in Tokyo and other seismically active areas.