Japan Geoscience Union Meeting 2015

Presentation information


Symbol H (Human Geosciences) » H-DS Disaster geosciences

[H-DS27] Tsunami and Tsunami Forecast

Wed. May 27, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Yutaka Hayashi(Meteorological Research Institute), Yuichi Namegaya(Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology)

6:15 PM - 7:30 PM

[HDS27-P08] An investigation of sea level fluctuation around the Tosashimizu Port by observed data

*Atsushi TANOBE1, Kentaro IMAI2, Yutaka HAYASHI3, Kuniaki ABE, Fumihiko IMAMURA4 (1.Graduate School of Engineering, Tohoku University, 2.IRIDeS, Tohoku University, 3.Meteorological Research Institute, 4.IRIDeS, Tohoku University)

Keywords:secondary undulation, spectrum, Tosashimizu

When a long wave such as tsunamis invades the harbor and port, secondary undulation may occur depending on the topography condition and the period of the tsunami. Such a secondary undulation is observed in past tsunami events.
The study for a water level change caused by natural period is accomplished a lot with observation data and numerical computation.
Those studies were achieved dominant period of the natural period from the fluctuations of sea level of the harbor and the topography condition and discussion about amplification factor.
In this study target at Tosashimizu port, Kochi and observed sea level at inside and outside the port. This study research for secondary undulation at Tosashimizu port.
2.observation data
In this study, install 7 pressure gauge in the Tosashimizu Port and, during periods from September 10, 2014 to December 9, 2014, observed a sea level by 15 seconds sampling interval. We used High-frequency filter to remove sea level variations associated with synoptic atmospheric activity. We divided that data into 2 types : period containing weather disturbance and the other.
We performed spectrum analysis for the these data and considered the characteristic of the secondary undulation in the Tosashimizu Port
In this study, We analyzed sea level data from September 10, 2014 to December 9, 2014 and examine characteristic of the secondary undulation in the Tosashimizu Port and got the following results.
3.1.From a result of the spectrum analysis of the not containing weather disturbance, the Tosashimizu port has strong peak around 20 minutes which are a natural period in the port. A peak begins to appear in around 40 minutes as approach the mouth of a port. On the other hand, out of the port has peaks seen around 40, 60 and 85 minutes.
3.2.From a result of the spectrum analysis of the containing weather disturbance, in the port, has strong peaks around 20 and 40 minutes. Out of the port has peaks around 30 and 75 minutes, on the other hand, not seen 40 minutes peak.
From the above results,
The period that spectrum peaks appears is different in inside and outside the port. In the Tosashimizu Port a state with different secondary undulation properties was confirmed in the inside and outside. In the containing weather disturbance period, the peak appear around 40 minutes is different from natural period and need to examination this peak generation factor.

This study received assistance to JSPS Grant in Aid for Scientific Research (B). I write it down here and express gratitude.

1.Kuniaki ABE(2011): Seiche dominant periods of bays and ports determind from a repeated measurement (2) Pacific coast of Southwest Japan, Nippon Dental College bulletin, vol.40, pp.23-30
2.SusumuTAKAHASHI(1986):Tsunami and Secondary Undulation in the Ishikari Bay, Bulletin of the Faculy of Engineering Hokkaido University, vol.130, pp.17-32
3.Hitoshi MURAKAMI, Tomio SHIMADA(1979):Consideration about the characteristic of the Secondary Undulation based on field data and the actual survey (2), Journal of JSCE B2 (shore engineering), vol.26 pp.129-132