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[SSS11-P26] Something is wrong with the Nankai earthquake
Keywords: The 1946 Showa Nankai Earthquake , The 1954 Ansei Nankai Earthquake
We are organizing historical earthquake documents by using GIS. Here, we describe the characteristics of the Ansei Nankai and Showa Nankai earthquakes in the southern Kii Peninsula.
<< The 1946 Showa Nankai Earthquake >>
The Showa Nankai Earthquake caused extensive damage, including 195 deaths and 2,442 houses completely destroyed in Wakayama Prefecture (“Kishu Saii Shi Zoku”, 1955). Crustal deformation has been observed in the southern part of the Kii Peninsula, with uplift at the southern end. This indicates that the fault extended to the Kii Peninsula. The tsunami also arrived a few minutes later in the southern part of the Kii Peninsula. This suggests that the large slip occurred quite close to the southern part of the peninsula.
There are many personal experiences about this earthquake. The shaking of this earthquake was large and lasted for a long time. The situation described in the experiences shows that there is almost no damage from earthquake shaking in Inan, Hayo, Susami, and Kushimoto, despite their proximity to the epicenter. Many people were sleeping because of the earthquake, which occurred at 4:19 in the early morning. Some people changed out of their nightgowns and evacuated, so the damage inside the houses does not seem to be so serious. The seismic intensity was about 4 to 5 (JMA). But soon after, huge tsunami devastated towns of north of Susami. Some people say that the tsunami was higher than the Ansei Nankai earthquake. According to Hatori (1980), the tsunami in the southern Kii Peninsula was about the same hight as the Ansei Nankai Earthquake. “Kishu Saii Shi Zoku” (1955) also pointed out that the damage caused by seismic motion was small, but the damage caused by tsunamis was much larger.
<< The 1954 Ansei Nankai Earthquake >>
According to Usami (1984), the seismic intensity in the southern Kii Peninsula was 4 to 5. Only areas with soft ground, such as Tanabe and Shingu, had an intensity of 6. Like the Showa Nankai Earthquake, seismic intensities of the Ansei Nankai Earthquake in the southern part of the Kii Peninsula were not large. Therefore, there are few historical records of the damage caused by shaking. In area of north of Susami, tsunami damages were severe. Many areas from Susami to Kushimoto were not damaged by the tsunami due to their slightly higher elevation. In the Tamaki Zen'emon records, such areas were described as "safe." If a house had collapsed due to the shaking, it would not be reported as “safe”.
The Ansei Nankai and Showa Nankai earthquakes are similar in that in the southern part of the Kii Peninsula, there was little damage from shaking, but the tsunami was large.
<< The 1946 Showa Nankai Earthquake >>
The Showa Nankai Earthquake caused extensive damage, including 195 deaths and 2,442 houses completely destroyed in Wakayama Prefecture (“Kishu Saii Shi Zoku”, 1955). Crustal deformation has been observed in the southern part of the Kii Peninsula, with uplift at the southern end. This indicates that the fault extended to the Kii Peninsula. The tsunami also arrived a few minutes later in the southern part of the Kii Peninsula. This suggests that the large slip occurred quite close to the southern part of the peninsula.
There are many personal experiences about this earthquake. The shaking of this earthquake was large and lasted for a long time. The situation described in the experiences shows that there is almost no damage from earthquake shaking in Inan, Hayo, Susami, and Kushimoto, despite their proximity to the epicenter. Many people were sleeping because of the earthquake, which occurred at 4:19 in the early morning. Some people changed out of their nightgowns and evacuated, so the damage inside the houses does not seem to be so serious. The seismic intensity was about 4 to 5 (JMA). But soon after, huge tsunami devastated towns of north of Susami. Some people say that the tsunami was higher than the Ansei Nankai earthquake. According to Hatori (1980), the tsunami in the southern Kii Peninsula was about the same hight as the Ansei Nankai Earthquake. “Kishu Saii Shi Zoku” (1955) also pointed out that the damage caused by seismic motion was small, but the damage caused by tsunamis was much larger.
<< The 1954 Ansei Nankai Earthquake >>
According to Usami (1984), the seismic intensity in the southern Kii Peninsula was 4 to 5. Only areas with soft ground, such as Tanabe and Shingu, had an intensity of 6. Like the Showa Nankai Earthquake, seismic intensities of the Ansei Nankai Earthquake in the southern part of the Kii Peninsula were not large. Therefore, there are few historical records of the damage caused by shaking. In area of north of Susami, tsunami damages were severe. Many areas from Susami to Kushimoto were not damaged by the tsunami due to their slightly higher elevation. In the Tamaki Zen'emon records, such areas were described as "safe." If a house had collapsed due to the shaking, it would not be reported as “safe”.
The Ansei Nankai and Showa Nankai earthquakes are similar in that in the southern part of the Kii Peninsula, there was little damage from shaking, but the tsunami was large.