10:45 AM - 12:15 PM
[SSS07-P04] Influence of shallow subsurface structure anisotropy to S-wave splitting - quantitative estimation with rotational seismograph
Keywords:S-wave splitting, Subsurface structure, Rotational Seismograph
S-waves generated at deep interior are separated into fast and slow ones pass through when the serpentinite layer on the upper surface of the subducting plate. The difference in arrival times of them is the product of the path length and the anisotropic intensity of the mantle wedge serpentinization. Thus, it allows us to understand the state of materials at metamorphosing boundary between plate and mantle wedge.
KC.AKR operated by Kochi Univ., has two seismometers, a short-period at 30 m borehole bottom and a broadband at the surface, observed clear S-waves splitting by the event (24 Jun. 2022 D=37km). However, the S-wave splitting details are different between two seismometers records. This different appearance is caused by superimposition of the angular changes with 30 m very small distance generated between two seismometers and the anisotropy at deep interior. In other words, even very shallow subsurface structure with anisotropy can change S-wave splitting appearance. At the time of the event, a rotational seismograph, BlueSeis-3A manufactured by iXblue, which has the same principle as a fiber gyro, was testing at KC.AKR, and we were able to observe the rotational angular velocity variations associated with the earthquake. In general, S-wave splitting appearance that is evaluated with seismographs usually installed at the ground surface, include the influence of surface structure. Therefore, the influence of the anisotropy by deep interior may be overestimated.
In this study, we evaluate the anisotropy of shallow surface structure by quantitative angular changes estimation based on direct observation with a rotational seismograph and by comparing subsurface-surface splitting difference.
Acknowledgments
We would like to express their gratitude to Ocean Winds kindly loaned iXblue BlueSeis-3A to us for a month-long period.
KC.AKR operated by Kochi Univ., has two seismometers, a short-period at 30 m borehole bottom and a broadband at the surface, observed clear S-waves splitting by the event (24 Jun. 2022 D=37km). However, the S-wave splitting details are different between two seismometers records. This different appearance is caused by superimposition of the angular changes with 30 m very small distance generated between two seismometers and the anisotropy at deep interior. In other words, even very shallow subsurface structure with anisotropy can change S-wave splitting appearance. At the time of the event, a rotational seismograph, BlueSeis-3A manufactured by iXblue, which has the same principle as a fiber gyro, was testing at KC.AKR, and we were able to observe the rotational angular velocity variations associated with the earthquake. In general, S-wave splitting appearance that is evaluated with seismographs usually installed at the ground surface, include the influence of surface structure. Therefore, the influence of the anisotropy by deep interior may be overestimated.
In this study, we evaluate the anisotropy of shallow surface structure by quantitative angular changes estimation based on direct observation with a rotational seismograph and by comparing subsurface-surface splitting difference.
Acknowledgments
We would like to express their gratitude to Ocean Winds kindly loaned iXblue BlueSeis-3A to us for a month-long period.