The bustling metropolis of Tokyo, with its population exceeding 30 million, faces a significant seismic threat due to its location atop multiple tectonic plates. Understanding past earthquakes is crucial for mitigating future disasters. The 1855 Ansei Edo earthquake, a magnitude 7.0 temblor, provides valuable insights into the potential for devastation. This quake, occurring during a period of societal upheaval as Japan opened its doors to the world after centuries of isolation, resulted in an estimated 10,000 deaths and the destruction of over 50,000 structures.
The Ansei Edo earthquake was not an isolated incident. It followed two major earthquakes in 1854, the Tokai and Nankai quakes, both registering a magnitude of 8.4. These three events highlight the volatile seismic nature of the region. The devastation caused by the 1855 quake was captured in vivid woodblock prints depicting the mythical giant catfish, Namazu, believed to be responsible for earthquakes.
Recently, researchers at the University of Tokyo uncovered a forgotten manuscript, the autobiography of Kabuki actor Nakamura Nakazo III, offering a unique perspective on the 1855 earthquake. Analysis of Nakamura’s original handwritten manuscript, Temae Miso, revealed crucial differences from later editions, providing clues about the quake’s depth.
Woodblock print depicting courtesans attacking the mythical catfish Namazu, blamed for earthquakes in Japan.
Nakamura’s account describes a short interval between the initial rumble (P-waves) and the violent shaking (S-waves). This short S-P interval, estimated at 5-10 seconds, suggests a relatively shallow depth of approximately 20 kilometers, placing the rupture within the subducting Philippine Sea plate. This finding contradicts previous estimates placing the depth at over 30 kilometers. Accurate depth estimation is critical for predicting ground shaking intensity and potential damage in future earthquakes. A shallower quake can cause significantly more surface damage than a deeper one.
The Japanese government estimates a 70% probability of another 1855-type earthquake occurring in Tokyo within the next 30 years, with a potential death toll of 23,000. Understanding the characteristics of historical earthquakes, like the 1855 Ansei Edo quake, is essential for developing effective mitigation strategies. Studying historical 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 partnered with historians from the University of Tokyo’s Historiographical Institute to decipher Nakamura’s cursive script and analyze historical records for seismic insights. This collaborative effort underscores the value of combining scientific and historical knowledge to enhance our understanding of past earthquakes and improve future preparedness. The team’s findings corroborate previous 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, analyzing various materials, including official reports, personal diaries, and visual records like pictures. Each type of historical material provides unique insights into past earthquake activity, helping researchers build a more comprehensive understanding of seismic risk. This long-term perspective is invaluable for assessing future earthquake hazards in Tokyo and other seismically active regions.
