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Your search keyword '"Yamanaka, Hiroaki"' showing total 358 results
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358 results on '"Yamanaka, Hiroaki"'

9. An assessment of uncertainties in VS profiles obtained from microtremor observations in the phased 2018 COSMOS blind trials

Author

Asten, Michael W., Yong, Alan, Foti, Sebastiano, Hayashi, Koichi, Martin, Antony J., Stephenson, William J., Cassidy, John F., Coleman, Jacie, Nigbor, Robert, Castellaro, Silvia, Chimoto, Kosuke, Cornou, Cécile, Cho, Ikuo, Hayashida, Takumi, Hobiger, Manuel, Kuo, Chun-Hsiang, Macau, Albert, Mercerat, E. Diego, Molnar, Sheri, Pananont, Passakorn, Pilz, Marco, Poovarodom, Nakhorn, Sáez, Esteban, Wathelet, Marc, Yamanaka, Hiroaki, Yokoi, Toshiaki, and Zhao, Don

Published
2022
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13. High-resolution spatial elastic wave velocity variation detected using multiple-linear-array microtremor measurements.

Author

Chimoto, Kosuke and Yamanaka, Hiroaki

Subjects
*GREEN'S functions, *ELASTIC waves, *MICROSEISMS, *SHEAR waves, *STATISTICAL correlation, *SURFACE waves (Seismic waves)
Abstract

We propose a method for capturing the near-surface elastic wave velocity variation using microtremors. The proposed method does not directly estimate the velocity of the medium; instead, it measures the spatial velocity change. We apply the stretching method, which is often used to detect the time variation of shear wave velocity based on the monitoring of seismic ambient noise, to microtremor recordings. Because spatially dense ambient noise records are unavailable, we performed microtremor measurements using multiple linear arrays with multiple sensors along the survey line to collect as many recordings as possible. The synchronised microtremor recordings of each array were used to compute the horizontal-to-vertical spectral ratio (H/V), cross-correlation (CC), autocorrelation (AC), and single-station cross-correlation (SC). The H/V ratio and the waveforms of these correlation functions showed significant spatial variation. The velocity variation was measured quantitatively using the stretching method, which correlates a compressed and stretched reference function with each function on the line. The velocity variation of the vertical and radial components of CC compares well with the variation of the H/V peak, indicating that the radial components of CC retrieved the Rayleigh-wave Green's function. The waveforms of AC and SC also showed spatial variation but the measured value of velocity change was smaller than that for CC. Further investigation is awaited to conclude if this is due to low-quality data or inappropriate measurement conditions. The reliability of the velocity change was confirmed by comparing the results to dispersion curves obtained using the conventional array method. [ABSTRACT FROM AUTHOR]

Published
2024
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28. Statistical analysis of source, path, and site spectra of S waves recorded at the S-net sites using spectral inversion technique

Author

Dhakal, Yadab, Kunugi, Takashi, Yamanaka, Hiroaki, Wakai, Atsushi, Aoi, Shin, and Nishizawa, Azusa

Abstract

S-net is a large-scale seafloor network in the Japan Trench area, consisting of inline-type 150 observatories with seismometers and pressure gauges. We analyzed the strong-motion data recorded at the S-net sites from earthquakes with magnitudes between about 4 and 7 with focal depths lower than 70 km. To minimize the effects of nonlinear site response and weak-couplings between the seabed and sensor houses, recordings with vector peak accelerations lower than 50 gals were selected. More than 6,000 recordings with high S/N ratios from about 600 earthquakes were used. Using the spectral inversion technique, we obtained some fundamental properties of the earthquake source spectra, path attenuation, and site factors from the horizontal-component S-wave portions of the recordings. The source spectra followed the source model generally well, and the estimated magnitudes were similar to the catalog magnitudes. The stress drops increased systematically with the focal depths, and the stress-drop values differed between the earthquake types. The path-averaged quality factors were somewhat larger than those in the past studies. The peak site frequencies ranged between about 0.2 and 10 Hz, while the peak amplification factors were between about 10 and 50. A moderate regionality was also observed in the distribution of site amplification factors. At some stations which were not buried, spurious site spectra were recognized. We discuss the above results and their implication in the presentation., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

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