5:15 PM - 6:45 PM
[SSS07-P07] Sources of primary microseisms strongly excited by hurricanes
Keywords:microseisms, hurricanes, ocean waves, ambient seismic noise
Primary microseisms are continuous ground motions with a frequency of 0.05 - 0.10 Hz. Since the frequency of primary microseisms corresponds to the frequency of the ocean wave swell, it is thought to be generated by the direct action of the shallow seafloor and ocean waves (Nishida et al., 2008; Fukao et al., 2010; Saito, 2010). In particular, it has been observed that the amplitude increases when an oceanic storm such as a typhoon or hurricane approaches. However, the sources and excitation mechanisms of the primary microseisms remain controversial. For example, Park & Hong (2020) and Kawakami and Suda (2022, the Seismological Society of Japan fall meeting) reported that the sources of primary microseisms excited by typhoons are concentrated in specific regions, but the cause is still unclarified. Similar phenomena were observed in the Northwest Atlantic, Kawakami and Suda (2023, the Seismological Society of Japan fall meeting) estimated the sources of 12 major hurricanes that occurred between 2017 and 2021, and found that primary microseisms were strongly excited in 3 locations: the Gulf of Mexico, the vicinity of the Bahamas, and the Gulf of Maine. However, the problem remained that the station distribution was biased and the number of hurricanes analyzed was small. In this study, we improved the bias of station distribution from Kawakami and Suda (2023, the Seismological Society of Japan fall meeting) and estimated the sources of primary microseisms for 41 hurricanes that occurred between 2017 and 2021.
For seismograph data, records at a total of 75 stations were used from 4 networks: GSN, USNSN, GASP in the Dominican Republic, and RSNC in Colombia. In addition, power spectra were generated every hour, and the three-component recording at the station where the peak of the primary microseisms was prominent was used for the analysis. For hurricanes, the National Hurricane Center database was referred to, we analyzed 41 hurricanes that occurred in the Atlantic from 2017 to 2021. For the estimation of the strong excitation source, the method using the polarity of the Rayleigh wave was used as in Park & Hong (2020). In this method, when the cross-correlation coefficient between a horizontal component rotated to a certain azimuth and a vertical component shifted in phase by π/2 is the largest, a source is considered to exist in that azimuth. In this study, the sources of strongly excited primary microseisms were estimated by setting virtual sources at 0.5 ° intervals in the range of 10 ° N to 50 ° N and 50 ° W to 100 ° W, and calculating the station averages of cross-correlation coefficients for each virtual source.
The analysis revealed that sources of primary microseisms are strongly excited in the Gulf of Mexico, the vicinity of the Bahamas, along the coast of the Dominican Republic, and in the Gulf of Maine. These regions are in good agreement with the sources of Stormquakes found in Fan et al. (2019). Stormquakes are 0.02 ~ 0.05 Hz coherent seismic waves generated when a hurricane approaches the coast. The finding that primary microseisms and Stormquakes that have different frequencies occur in similar regions suggests that these mechanisms may be similar. The presentation will also include comparisons with seafloor topography and pressure fluctuations on the seafloor.
For seismograph data, records at a total of 75 stations were used from 4 networks: GSN, USNSN, GASP in the Dominican Republic, and RSNC in Colombia. In addition, power spectra were generated every hour, and the three-component recording at the station where the peak of the primary microseisms was prominent was used for the analysis. For hurricanes, the National Hurricane Center database was referred to, we analyzed 41 hurricanes that occurred in the Atlantic from 2017 to 2021. For the estimation of the strong excitation source, the method using the polarity of the Rayleigh wave was used as in Park & Hong (2020). In this method, when the cross-correlation coefficient between a horizontal component rotated to a certain azimuth and a vertical component shifted in phase by π/2 is the largest, a source is considered to exist in that azimuth. In this study, the sources of strongly excited primary microseisms were estimated by setting virtual sources at 0.5 ° intervals in the range of 10 ° N to 50 ° N and 50 ° W to 100 ° W, and calculating the station averages of cross-correlation coefficients for each virtual source.
The analysis revealed that sources of primary microseisms are strongly excited in the Gulf of Mexico, the vicinity of the Bahamas, along the coast of the Dominican Republic, and in the Gulf of Maine. These regions are in good agreement with the sources of Stormquakes found in Fan et al. (2019). Stormquakes are 0.02 ~ 0.05 Hz coherent seismic waves generated when a hurricane approaches the coast. The finding that primary microseisms and Stormquakes that have different frequencies occur in similar regions suggests that these mechanisms may be similar. The presentation will also include comparisons with seafloor topography and pressure fluctuations on the seafloor.