Tidal Level Changes Observed in Hokkaido around 13:00 on August 2
Around the time of the earthquake (M6.4) off-shore west of Sakhalin at 11:37 on August 2, 2007 (JST), tidal level changes were observed in Rumoi and Wakkanai, Hokkaido. (Figure A) At first, these were considered to be tsunamis caused by the earthquake. However the ensuing investigation (see the following) showed that the changes were most likely associated with passing of meteorological disturbances.
- According to the seismic wave analysis, the earthquake is not considered to be highly tsunami-genic (tsunami earthquake).
- Observed tidal level changes were largely different from the results of tsunami simulations (amplitude, period and arrival time). (Figure B)
- The time of a sudden change in atmospheric pressure at Rumoi that was caused by a meteorological disturbance (Figure C), is nearly consistent with the tidal level changes (Figure D). Also the period of the tidal level changes are the same as that of the other undulations.
In addition, in the vicinity of the earthquake on southern Sakhalin, tsunamis of 0.1–0.2m high were observed (NOAA). Therefore, there might be a possibility that those tsunamis are partially related to the tidal level changes observed in Hokkaido.
Japan Meteorological Agency
[Seismic Activity for August 2007 (September 10, 2007)]