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[SGD03-P04] Tilt changes observed in Kobe due to the suboscillations in Osaka Bay
Keywords:tilt change, Osaka Bay, suboscillation
Tilt changes observed at Rokko-Futatabi station in Kobe have some definite signals with a period of 2.5 to 6.2 hours. The periods of these signals are close to those of suboscillations occurring in Osaka Bay. In this study, I calculated the spatial distributions of sea level variations due to suboscillations in Osaka Bay numerically, and confirmed that the tilt changes observed at the Rokko-Futatabi station could be caused by the oceanic loading of the suboscillations.
The water-tube tiltmeter is installed in the north-south direction in Rokko-Futatabi station, and the continuous observation of tilt changes has been performed at 0.1 second intervals. I removed the tidal changes and the atmospheric pressure effect by applying the tidal analysis program ‘BAYTAP-G’ (Tamura et al.,1991) to the observed tilt changes, and investigated the frequency characteristics of the tilt residuals by using FFT. The tilt residuals have definite signals with periods of 2.5, 3.5, 4.9, and 6.2 hours. Their amplitudes were not stable and showed fluctuations along time lapse.
These tilt changes are presumed to be caused by oceanic loading. The sea level changes observed at the tide stations, JMA, around Osaka Bay have definite signals with periods of 2.5, 4.2, 5.0, and 6.1 hours. These periods are close to those of the tilt residuals mentioned above. Osaka Bay is about 55 km to the northeast and 30 km to the northwest with an average depth of about 30 m. In this bay, the suboscillations are analytically predicted to occur with a period of 2 to 4 hours. I numerically calculated the sea level variations in Osaka Bay with incoming regular waves from the Akashi Strait or Kii Channel, and confirmed the suboscillations with periods of 2.2, 3.6, 5.2 and 6.1 hours. Therefor, it is considered that those tilt signals with period of 2.5 to 6.2 hours were caused by the oceanic loading due to the suboscillation in Osaka Bay.
In this study, I calculated tilt changes due to oceanic loadings by using the suboscillations observed at tide stations and the numerical distributions of sea level variations in Osaka Bay, and confirmed that the tilt signals at Rokko-Futatabi station could be caused by the suboscillations. The Rokko-Futatabi station is located about 0.6 km south of the Mampukuji Fault with the east-west strike. Mukai et al. (2018) showed that strain changes observed during typhoon passage were influenced by groundwater flow within the fracture zone of the fault. I also investigated that seasonal pore pressure changes could affect the tilt changes due to the suboscillations.
The water-tube tiltmeter is installed in the north-south direction in Rokko-Futatabi station, and the continuous observation of tilt changes has been performed at 0.1 second intervals. I removed the tidal changes and the atmospheric pressure effect by applying the tidal analysis program ‘BAYTAP-G’ (Tamura et al.,1991) to the observed tilt changes, and investigated the frequency characteristics of the tilt residuals by using FFT. The tilt residuals have definite signals with periods of 2.5, 3.5, 4.9, and 6.2 hours. Their amplitudes were not stable and showed fluctuations along time lapse.
These tilt changes are presumed to be caused by oceanic loading. The sea level changes observed at the tide stations, JMA, around Osaka Bay have definite signals with periods of 2.5, 4.2, 5.0, and 6.1 hours. These periods are close to those of the tilt residuals mentioned above. Osaka Bay is about 55 km to the northeast and 30 km to the northwest with an average depth of about 30 m. In this bay, the suboscillations are analytically predicted to occur with a period of 2 to 4 hours. I numerically calculated the sea level variations in Osaka Bay with incoming regular waves from the Akashi Strait or Kii Channel, and confirmed the suboscillations with periods of 2.2, 3.6, 5.2 and 6.1 hours. Therefor, it is considered that those tilt signals with period of 2.5 to 6.2 hours were caused by the oceanic loading due to the suboscillation in Osaka Bay.
In this study, I calculated tilt changes due to oceanic loadings by using the suboscillations observed at tide stations and the numerical distributions of sea level variations in Osaka Bay, and confirmed that the tilt signals at Rokko-Futatabi station could be caused by the suboscillations. The Rokko-Futatabi station is located about 0.6 km south of the Mampukuji Fault with the east-west strike. Mukai et al. (2018) showed that strain changes observed during typhoon passage were influenced by groundwater flow within the fracture zone of the fault. I also investigated that seasonal pore pressure changes could affect the tilt changes due to the suboscillations.