10:45 AM - 11:00 AM
[SSS11-06] Directionally dependent horizontal-to-vertical spectral ratios of microtremors across Active Faults in Ogasawara Iwo-To Island
Keywords:Active fault, Microtremor, H/V Spectral Ratio, Ogasawara Iwo-To Island
Ogasawara Iwo-To island is an active volcano, and crustal deformation with uplift of about 1 m per year has been continuously observed; a new island was also formed by eruptive activity on the seafloor off the south coast of Ogasawara Iwo-To island that became active from October 2023. Active faults on Ogasawara Iwo-To island have been reported at several locations on the western and northeastern sides of the island.
Murakoshi (2023, 16JEES) used microtremor data in the vicinity of an active fault in the northeastern part of Iwo-To island, Ogasawara, to image the line-of-sight direction using predominant frequency, amplitude, and anisotropy of the H/V spectral ratio. As a result, we were able to detect changes in spatial patterns that can be inferred to be horizontal heterogeneity structures caused by subterranean faults.
In this study, we conducted a new tight-lattice microtremor observation in the vicinity of the inferred underground fault and analyzed the azimuthal dependence of the microtremor H/V spectral ratio. In this study, microtremor observations were made at intervals of 2 m, whereas in the previous study, microtremor observations were made at intervals of 10 m or 25 m in the vicinity of the fault. The instrument used was a JU410, and measurements were made continuously for at least 15 minutes at each observation point at a sampling frequency of 200 Hz for three components: horizontal (east-west and north-north) and vertical. We would like to introduce previous studies on the azimuthal dependence of the microtremor H/V spectral ratio, analyze the results, and describe the characteristics.
Acknowledgments:
The authors used the BIDO program, which was downloaded from https://staff.aist.go.jp/ikuo-chou, for the analyses of the H/V spectral ratios.
Murakoshi (2023, 16JEES) used microtremor data in the vicinity of an active fault in the northeastern part of Iwo-To island, Ogasawara, to image the line-of-sight direction using predominant frequency, amplitude, and anisotropy of the H/V spectral ratio. As a result, we were able to detect changes in spatial patterns that can be inferred to be horizontal heterogeneity structures caused by subterranean faults.
In this study, we conducted a new tight-lattice microtremor observation in the vicinity of the inferred underground fault and analyzed the azimuthal dependence of the microtremor H/V spectral ratio. In this study, microtremor observations were made at intervals of 2 m, whereas in the previous study, microtremor observations were made at intervals of 10 m or 25 m in the vicinity of the fault. The instrument used was a JU410, and measurements were made continuously for at least 15 minutes at each observation point at a sampling frequency of 200 Hz for three components: horizontal (east-west and north-north) and vertical. We would like to introduce previous studies on the azimuthal dependence of the microtremor H/V spectral ratio, analyze the results, and describe the characteristics.
Acknowledgments:
The authors used the BIDO program, which was downloaded from https://staff.aist.go.jp/ikuo-chou, for the analyses of the H/V spectral ratios.