4:00 PM - 4:15 PM
[MIS27-06] Analysis of aftershocks of the 1855 Ansei Edo Earthquake using old documents discovered around Kanto Ko-Shinetsusing old documents discovered around Kanto Ko-Shinetsu
The 1855 Ansei Edo earthquake occurred around pm 9 of November 11 1855 and caused damage in Edo and around Kanto area by strong shaking. Usami (2001) estimated the epicenter of the mainshock in Northern part of Tokyo bay. For this earthquake, there are many historical documents which show the details of the aftershock activity as well as the main shock. We analyzed the aftershock activity of Ansei Edo earthquake by using “Ebihara-ke Document” discovered in the beginning of 2000 and “Ohya-ke Daily” introduced in Tsuji (2003) in addition to published historical collection of earthquakes.
We focused on temporal changes of aftershock activity of Ansei Edo earthquake. We compared the records of earthquake written in “Ansei Jishin Kakitome no Koto” in “Ebihara-ke Document” with those in the old document that has detailed record of aftershock activity in Edo, for example, “Yaburemado no Ki.” We also examined difference between the number of records in daytime and night. There are various possible reasons for the difference in the number of aftershocks recorded in each document, such as the differences in the temporal resolution of earthquakes in each archive or the differences in the seismic intensity due to differences in the epicenter and magnitude of each aftershock. In this study, we applied the Omori-Utsu formula to the aftershock records in "Ansei Jishin Kakitome no Koto", and found a good agreement between the curve of the Omori-Utsu formula applied to " Ansei Jishin Kakitome no Koto " and the number of aftershocks recorded by historical documents in Edo after the third day of the main earthquake.This suggests that the "Ansei Jishin Kakitome no Koto" may have recorded aftershocks that were overlooked by some historical documents in Edo such as the “Yaburemado no Ki”.
Next, we focused on the spatial distribution of aftershock activity of the Ansei Edo earthquake. We categorized the discription on the day when aftershock occurred into four categories: "no articles", "articles without earthquake records," "articles with earthquake records," and "articles with large earthquake records," and plotted them on a map to see the distribution of felt records for each aftershock. Then, using this map, we estimated the felt area of four aftershocks, including the earthquake of November 17 1855, which is considered to be the largest aftershock of the Ansei Edo Earthquake. We compared the time of occurrence and shaking characteristics of the earthquake on November 17 1855, which is regarded as the largest aftershock by Nakamura and Matsu'ura (2011). It was found two earthquakes occured, one at dusk and the other at night, and that the sensitivities may have differed. We also compared the distribution of seismic intensity between aftershocks and main shock.
There are various possibilities for the difference of felt distribution between the aftershock and the mainshock obtained in this study, such as the difference in the location and magnitude of the epicenters of the mainshock and aftershocks, the difference in the accuracy of time of the respective records, and the inclusion of earthquakes not included in the aftershock sequences of the Ansei-Edo Earthquake or earthquakes that occurred in the other region.
We focused on temporal changes of aftershock activity of Ansei Edo earthquake. We compared the records of earthquake written in “Ansei Jishin Kakitome no Koto” in “Ebihara-ke Document” with those in the old document that has detailed record of aftershock activity in Edo, for example, “Yaburemado no Ki.” We also examined difference between the number of records in daytime and night. There are various possible reasons for the difference in the number of aftershocks recorded in each document, such as the differences in the temporal resolution of earthquakes in each archive or the differences in the seismic intensity due to differences in the epicenter and magnitude of each aftershock. In this study, we applied the Omori-Utsu formula to the aftershock records in "Ansei Jishin Kakitome no Koto", and found a good agreement between the curve of the Omori-Utsu formula applied to " Ansei Jishin Kakitome no Koto " and the number of aftershocks recorded by historical documents in Edo after the third day of the main earthquake.This suggests that the "Ansei Jishin Kakitome no Koto" may have recorded aftershocks that were overlooked by some historical documents in Edo such as the “Yaburemado no Ki”.
Next, we focused on the spatial distribution of aftershock activity of the Ansei Edo earthquake. We categorized the discription on the day when aftershock occurred into four categories: "no articles", "articles without earthquake records," "articles with earthquake records," and "articles with large earthquake records," and plotted them on a map to see the distribution of felt records for each aftershock. Then, using this map, we estimated the felt area of four aftershocks, including the earthquake of November 17 1855, which is considered to be the largest aftershock of the Ansei Edo Earthquake. We compared the time of occurrence and shaking characteristics of the earthquake on November 17 1855, which is regarded as the largest aftershock by Nakamura and Matsu'ura (2011). It was found two earthquakes occured, one at dusk and the other at night, and that the sensitivities may have differed. We also compared the distribution of seismic intensity between aftershocks and main shock.
There are various possibilities for the difference of felt distribution between the aftershock and the mainshock obtained in this study, such as the difference in the location and magnitude of the epicenters of the mainshock and aftershocks, the difference in the accuracy of time of the respective records, and the inclusion of earthquakes not included in the aftershock sequences of the Ansei-Edo Earthquake or earthquakes that occurred in the other region.