10:45 AM - 12:15 PM
[SSS07-P11] Comparison of primary microseisms sources during typhoons with ocean waves and seafloor topography
Keywords:Microseisms, typhoon, ocean waves, ambient seismic noise
Among the background noise in seismograph records, the oscillations in the frequency band of 0.05 -0.10 Hz are called primary microseisms. Although primary microseisms are thought to be generated by the coupling between ocean waves and the seafloor, there has been little quantitative discussion on the excitation mechanism. Investigation of the excitation mechanism of microseisms is important not only for understanding the interaction between atmosphere, ocean, and solid earth but also for applied research such as the elucidation of the earth’s internal structure and prediction of ocean waves using microseisms. In this study, as the first step for quantitative discussion about excitation mechanism, we compared the source regions of primary microseisms excited by strong typhoons approaching Japan estimated in our previous study with significant wave data predicted by WAVEWATCH III and seafloor topography.
We used F-net broadband records provided by NIED and significant wave height and significant wave period data predicted by using WAVEWATCH III provided by NOAA. We analyzed these data in the period during strong typhoons with maximum wind speeds of 33 m/s or more approached Japan with reference to "Past Typhoon Information" provided by JMA. We also used the seafloor topography data from the digital elevation model SRTM15+ with a spatial sampling interval of 15-sec arc.
Previous our studies have revealed that the source regions of the primary microseisms move approximately along with typhoons, while there are periods when the source regions remain stationary in the Nansei Islands and Izu Islands regions regardless of the movement of typhoons. It is considered that primary microseisms are particularly strongly excited in the stagnant regions. The estimated source regions are well correlated with the spatial distribution of significant wave height and significant wave period: the significant wave height is high and the significant wave period is long in and around the stagnant regions. Compared with the seafloor topography, the estimated source regions are coastal area or regions with relatively shallow water depth and complex topography. These results suggest that the strong excitations of primary microseisms during the typhoon approaches are due to the strong excitation of ocean waves in the regions with shallow water depth and complex seafloor topography.
We used F-net broadband records provided by NIED and significant wave height and significant wave period data predicted by using WAVEWATCH III provided by NOAA. We analyzed these data in the period during strong typhoons with maximum wind speeds of 33 m/s or more approached Japan with reference to "Past Typhoon Information" provided by JMA. We also used the seafloor topography data from the digital elevation model SRTM15+ with a spatial sampling interval of 15-sec arc.
Previous our studies have revealed that the source regions of the primary microseisms move approximately along with typhoons, while there are periods when the source regions remain stationary in the Nansei Islands and Izu Islands regions regardless of the movement of typhoons. It is considered that primary microseisms are particularly strongly excited in the stagnant regions. The estimated source regions are well correlated with the spatial distribution of significant wave height and significant wave period: the significant wave height is high and the significant wave period is long in and around the stagnant regions. Compared with the seafloor topography, the estimated source regions are coastal area or regions with relatively shallow water depth and complex topography. These results suggest that the strong excitations of primary microseisms during the typhoon approaches are due to the strong excitation of ocean waves in the regions with shallow water depth and complex seafloor topography.