[S-SS24] Earthquake prediction and forecast

[SSS24-P02] How often do the abnormal phenomena witnessed just before 1946 Nankai earthquake appear (1)

*Yasuhiro Umeda¹, Satoshi Itaba¹ (1.Advanced Industrial Science and Technology)

Keywords:1946 Nankai earthquake, witness

Abnormal phenomena such as well water decreases or sea level changes has been witnessed just before the 1946 Nankai earthquake. In the Pacific Ocean coastal area of Shikoku from Kii peninsula, such phenomena have been witnessed in 24 locations. It has been witnessed that about 2m decrease of well water, maximum 3m lowering of sea level and about 0.5m of secondary undulation. It has been stable weather before the main shock. Do the witnessed abnormal phenomena has appeared only just before the main shock? Or do they occasionally appear? Based on the recent observation data, we examined the frequency with that the same phenomena as witnessed just before the main shock. The water level of three wells which have been reported the decreased water before the main shock have been observed continuously by AIST. In recent two years data, it was not found that the well water steeply decreases by more than 2m. We have searched the sea level departure at Kushimoto, Muroto cape and Kochi, on the JMA website. In 2003 - 2014, we could not find the sea level departure of more than -2m. The secondary undulations at Muroto cape were checked on the JMA website. In 2006-2014, there were 17 times of the secondary undulations more than 0.5m. All cases were caused by the weather. Within this survey, we could not find the similar abnormal phenomena which were witnessed just before the main shock.