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[MIS22-10] Seismic Activity in Southern Miyagi Prefecture in the 18th Century Based on the Microfilmed Records of the Takano Family
Diary records in the past are useful for historical earthquake research including seismic activity. For example, Satake and Ishibe (2020) estimated the detection thresholds of earthquake records written in diaries in Edo (Tokyo), Japan and examined long-term changes in seismic activity. Usami et al. (2001) compared earthquakes recorded in diaries in Morioka and Yamagata, northern Japan, with modern catalogs, and examined the correspondence between the expression of shaking and seismic intensity.
In this study, we focused on the number of felt earthquakes recorded in the “Takano family records”. We used the "Addendum of historical documents on earthquakes in Japan, Vol. 5, No. 1" and microfilms archived in the Tohoku University Library.The Takano family is a vassal of the Sendai clan. The records cover 86 years from 1696 to 1782. The Takano family had an estate in Hirasawa (Zao Town, Miyagi prefecture), and ruled the area for 250 years during the Edo period. The earthquake records were recorded by the 19th head of the family, Tomokane, and the 20th head of the family, Hirokane. Their records contain detailed descriptions of daily life, weather, and earthquakes in Sendai and Hirasawa. The period of record is June 1, 1737 - February 7, 1782 for Tomokane, and February 9, 1766 - September 14, 1770 for Hirokane.
The number of days recorded for earthquakes in Hirasawa and Sendai was 238 days for Tomokane and 110 days for Hirokane. From the examination of the microfilm of the original records 73 days of earthquakes were newly found for Tomokane and 6 days for Hirokane that were not collected in the previous collections of historical documents on earthquakes.
Earthquakes felt in Miyagi Prefecture can be roughly divided into those that occur along the Japan Trench and those that occur inland. In the case of earthquakes along the Japan Trenchnot only earthquakes off Miyagi Prefecture but also earthquakes off Ibaraki Prefecture and off Aomori Prefecture can also cause damage in southern Miyagi Prefecture. Earthquakes inland are known to occur in active faults such as the Nagamachi-Rifu line fault zone and the fault zone on the western edge of the Fukushima Basin, as well as swarm earthquakes such as those on Mt.Kurikoma and Mt. Zao. Enda Observatory in Zao town has been set up near Hirasawa since March 2002, and has observed earthquakes with seismic intensity ranging from 1 to 6 on the JMA intensity scale. On average, 94 seismic intensity 1 events and 33 seismic intensity 2 events have been recorded in one year from 2003 to 2020.
Comparison of the records of earthquakes recorded in the “Takano family records” with those recorded by modern intensity observationshows that the author of the Takano family records recorded earthquakes with intensity 2 or higher and some of those withintensity 1.
The earthquakes listed in the “Takano family records” were classified by the type of occurrence, taking into account the felt records in other historical documents. We classified the earthquakes into three types: earthquakes in the Japan Trench, inland earthquakes and earthquakes on the Japan Sea side, and others. As a result, 40% of earthquakes recorded in the "Takano Family Records" are considered to be earthquakes in the Japan Trench and 10% are considered to be earthquakes inland or on the Japan Sea side. The details are not known for 50% of the earthquakes because there are no other historical documents with felt records. Of these, earthquakes were recorded in Hirasawa for 18 days out of 61 days from September 29, 1769 to November 28, 1769, a total of 19 times. In 1769, the number of earthquakes recorded in the “Takano family records” was 24, which means that about 80% of the year's earthquakes were recorded in these 61 days. It is possible that these earthquakes are records of a swarm in the western margin fault zone of the Fukushima Basin and/or Mt. Zao.
In this study, we focused on the number of felt earthquakes recorded in the “Takano family records”. We used the "Addendum of historical documents on earthquakes in Japan, Vol. 5, No. 1" and microfilms archived in the Tohoku University Library.The Takano family is a vassal of the Sendai clan. The records cover 86 years from 1696 to 1782. The Takano family had an estate in Hirasawa (Zao Town, Miyagi prefecture), and ruled the area for 250 years during the Edo period. The earthquake records were recorded by the 19th head of the family, Tomokane, and the 20th head of the family, Hirokane. Their records contain detailed descriptions of daily life, weather, and earthquakes in Sendai and Hirasawa. The period of record is June 1, 1737 - February 7, 1782 for Tomokane, and February 9, 1766 - September 14, 1770 for Hirokane.
The number of days recorded for earthquakes in Hirasawa and Sendai was 238 days for Tomokane and 110 days for Hirokane. From the examination of the microfilm of the original records 73 days of earthquakes were newly found for Tomokane and 6 days for Hirokane that were not collected in the previous collections of historical documents on earthquakes.
Earthquakes felt in Miyagi Prefecture can be roughly divided into those that occur along the Japan Trench and those that occur inland. In the case of earthquakes along the Japan Trenchnot only earthquakes off Miyagi Prefecture but also earthquakes off Ibaraki Prefecture and off Aomori Prefecture can also cause damage in southern Miyagi Prefecture. Earthquakes inland are known to occur in active faults such as the Nagamachi-Rifu line fault zone and the fault zone on the western edge of the Fukushima Basin, as well as swarm earthquakes such as those on Mt.Kurikoma and Mt. Zao. Enda Observatory in Zao town has been set up near Hirasawa since March 2002, and has observed earthquakes with seismic intensity ranging from 1 to 6 on the JMA intensity scale. On average, 94 seismic intensity 1 events and 33 seismic intensity 2 events have been recorded in one year from 2003 to 2020.
Comparison of the records of earthquakes recorded in the “Takano family records” with those recorded by modern intensity observationshows that the author of the Takano family records recorded earthquakes with intensity 2 or higher and some of those withintensity 1.
The earthquakes listed in the “Takano family records” were classified by the type of occurrence, taking into account the felt records in other historical documents. We classified the earthquakes into three types: earthquakes in the Japan Trench, inland earthquakes and earthquakes on the Japan Sea side, and others. As a result, 40% of earthquakes recorded in the "Takano Family Records" are considered to be earthquakes in the Japan Trench and 10% are considered to be earthquakes inland or on the Japan Sea side. The details are not known for 50% of the earthquakes because there are no other historical documents with felt records. Of these, earthquakes were recorded in Hirasawa for 18 days out of 61 days from September 29, 1769 to November 28, 1769, a total of 19 times. In 1769, the number of earthquakes recorded in the “Takano family records” was 24, which means that about 80% of the year's earthquakes were recorded in these 61 days. It is possible that these earthquakes are records of a swarm in the western margin fault zone of the Fukushima Basin and/or Mt. Zao.