EGU2020-3999
https://doi.org/10.5194/egusphere-egu2020-3999
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Stability of ambient noise H/V spectra obtained from OBS near the Japan Trench

Atikul Haque Farazi, Emmanuel Soliman M. Garcia, and Yoshihiro Ito
Atikul Haque Farazi et al.
  • Disaster Prevention Research Institute, Division of Earth and Planetary Science, Kyoto University, Kyoto, Japan (farazi.haque.38w@st.kyoto-u.ac.jp)

Ocean bottom seismometers (OBS) are widely in use since recent past to monitor seismicity of slow earthquakes as well as that of ordinary earthquakes. Seismic velocity structures, especially of S-wave are essential to estimate hypocenters of them with accuracy. Here we focus on spatial and temporal stability of ambient noise horizontal to vertical spectral ratio (H/V) spectra calculated from ocean bottom seismometers, as the first step toward future application of ambient noise H/V to estimate S-wave velocity structure. We aim to use the Nakamura’s method (1989) for ambient noise H/V spectra using a 3-component OBS array in the Japan Trench, to image deep structure above the plate interface near the trench. To achieve the imaging, it is necessary to examine spatial and temporal stability of the derived H/V spectra from these seismometers. First, we split each 24-hours record into 1-hour windows after removing the instrumental response, Then, Fourier amplitude spectra of each component is taken and smoothed using Konno and Ohmachi (1998) method, with applying downsampling, mean and trend removal, and tapering to each window. Finally, a 1-hour H/V spectral ratio is calculated with taking quadratic mean of two horizontal components. However, a total of 21 OBS, 3 broadband and 18 short-period, stations have been used in this study. A daily variation and stability of the H/V spectra are examined along with comparing them spatially from one station to another. Stability of the H/V spectra from OBS is promising for carrying out our future endevour of deeper observation using the ambient noise H/V method.

How to cite: Farazi, A. H., Garcia, E. S. M., and Ito, Y.: Stability of ambient noise H/V spectra obtained from OBS near the Japan Trench, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3999, https://doi.org/10.5194/egusphere-egu2020-3999, 2020

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Presentation version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-3999, Vincenzo Serlenga, 05 May 2020

    Hi, 

    why do you remove instrumental response before computing H/V? Are the components characterized by a different instrumental response?

    Best regards,

    Vincenzo

  • AC1: Comment on EGU2020-3999, Atikul Haque Farazi, 05 May 2020

    Hi, thanks for your comment.

    No, they have same instrumental response, but I got the data as instrumental resonse corrected, so I mention it. Also, most of the papers mention about instrumental response correction before H/V calculation! Please let me know if you have further opinion.

    • CC2: Reply to AC1, Vincenzo Serlenga, 06 May 2020

      Thank you for your reply.

      Well, I am not saying it is wrong, but in my opinion it is not strictly necessary, since you are performing a spectral ratio. If the instrument response is common to the three components, by performing the ratio it (the instr. response) will be automatically cancelled out, isn't it?

      Best regards,

      Vincenzo

      • AC2: Reply to CC2, Atikul Haque Farazi, 06 May 2020

        Hi there,

        Thanks for further discussion. I got your point, but sometimes componets, especially the horizontals and the vertical one have subtle different response! Especially for H/V they don't have the same amplification. This is just my observation, not sure even if it is theoritically correct.