11:15 AM - 11:30 AM
[SSS14-09] An earthquake and a tsunami may have occurred in the Suruga Bay in the 13th century.
Keywords:Suruga Bay, tsunami, liquefaction-induced feature, Nankai Trough, tsunami deposit
In the late 13th century, major earthquakes such as the Shoka (1257) and Einin (1293) earthquakes are known to have occurred in the southern Kanto region. A significant number of deaths and injuries were documented in Kamakura in the 1293 earthquake, and the earthquake is considered to have been a plate boundary earthquake occurred in the Sagami Trough (Ishibashi, 1991). In addition, although there is no direct description of a tsunami, written documents also show that many bodies were found on the beach, suggesting that the 1293 earthquake may have been accompanied by a tsunami (Ishibashi, 2018). On the other hand, the 1257 Shoka Earthquake is documented to have caused damage to shrines and temples and liquefaction in Kamakura, but there are little descriptions of human loss, and it is believed that the damage was smaller than that of the 1293 Einin Earthquake (Ishibashi, 2018).
Two traces of seismic shaking (liquefaction-induced features) dated the 9–13th century and the late 13th century and later were found at the Agetsuchi archaeological site on the west coast of the Suruga Bay (Yada and Suzuki, 1996). The two earthquake traces have been considered to represent two different earthquakes. However, since these earthquake traces were found at the same archaeological site and their ages overlap with each other, the possibility that they were produced by the same earthquake should be addressed. If we assume that the two earthquake traces were simultaneously produced by a single earthquake, the date of the earthquake is constrained to the later 13th century.
An event deposit formed by seawater inundation was found at the Ida Lowland on the east coast of the Suruga Bay (Sawai et al., 2016). We calculated the age of the event deposit using radiocarbon ages provided by Sawai et al. (2016) with the Phase Model of OxCal v.4.4.4. Consequently, we obtained ages of 1143–1281 AD for the 1σ age range and 1062–1333 AD for the 2σ age range. The Shoka Earthquake (1257) is within the 1σ age range, and the Einin Earthquake(1293) and the Eicho Earthquake (1096), which is thought to have occurred in the eastern part of the Nankai Trough, are within the 2σ age range.
In Numazu, on the east coast of the Suruga Bay, it is recorded that in 1258, the year after the Shoka Earthquake (1257), Saint Nichiren prayed for quieting tsunamis at the request of residents who suffered from tsunami damage (Tsuji, 1993). Based on the fact that the timing of Nichiren's visit was very close to the earthquake, Tsuji (1993) proposed the possibility that the Shoka Earthquake (1257) was occurred in the Suruga Bay. As Ishibashi (1999) pointed out, this hypothesis was based solely on the records in Numazu and was somewhat less plausible. However, the age of the earthquake traces at the Agetsuchi site and the event deposit in the Ida lowland overlap with the Shoka earthquake (1257), and these facts support the hypothesis of Tsuji (1993). Moreover, if we assume that the Shoka Earthquake (1257) occurred in the Suruga Bay, we can reasonably explain why the damage from the Shoka Earthquake in Kamakura was smaller than that of the Einin Earthquake (1293).
Two traces of seismic shaking (liquefaction-induced features) dated the 9–13th century and the late 13th century and later were found at the Agetsuchi archaeological site on the west coast of the Suruga Bay (Yada and Suzuki, 1996). The two earthquake traces have been considered to represent two different earthquakes. However, since these earthquake traces were found at the same archaeological site and their ages overlap with each other, the possibility that they were produced by the same earthquake should be addressed. If we assume that the two earthquake traces were simultaneously produced by a single earthquake, the date of the earthquake is constrained to the later 13th century.
An event deposit formed by seawater inundation was found at the Ida Lowland on the east coast of the Suruga Bay (Sawai et al., 2016). We calculated the age of the event deposit using radiocarbon ages provided by Sawai et al. (2016) with the Phase Model of OxCal v.4.4.4. Consequently, we obtained ages of 1143–1281 AD for the 1σ age range and 1062–1333 AD for the 2σ age range. The Shoka Earthquake (1257) is within the 1σ age range, and the Einin Earthquake(1293) and the Eicho Earthquake (1096), which is thought to have occurred in the eastern part of the Nankai Trough, are within the 2σ age range.
In Numazu, on the east coast of the Suruga Bay, it is recorded that in 1258, the year after the Shoka Earthquake (1257), Saint Nichiren prayed for quieting tsunamis at the request of residents who suffered from tsunami damage (Tsuji, 1993). Based on the fact that the timing of Nichiren's visit was very close to the earthquake, Tsuji (1993) proposed the possibility that the Shoka Earthquake (1257) was occurred in the Suruga Bay. As Ishibashi (1999) pointed out, this hypothesis was based solely on the records in Numazu and was somewhat less plausible. However, the age of the earthquake traces at the Agetsuchi site and the event deposit in the Ida lowland overlap with the Shoka earthquake (1257), and these facts support the hypothesis of Tsuji (1993). Moreover, if we assume that the Shoka Earthquake (1257) occurred in the Suruga Bay, we can reasonably explain why the damage from the Shoka Earthquake in Kamakura was smaller than that of the Einin Earthquake (1293).