Obayashi Corporation

About: Obayashi Corporation is a company organization based out in Tokyo, Japan. It is known for research contribution in the topics: Damper & Pile. The organization has 580 authors who have published 520 publications receiving 7363 citations. The organization is also known as: Kabushiki-gaisha Ōbayashi Gumi.

A Comparison of ESAC and FK Methods of Estimating Phase Velocity Using Arbitrarily Shaped Microtremor Arrays

Abstract: Focusing on a comparison of the accuracy of the extended spatial autocorrelation (ESAC) method and the frequency–wavenumber spectrum (FK) method, we carried out short-period microtremor measurements of arbitrarily shaped array configurations at a site with a well-known velocity structure at shallow depths. Using both techniques, we measured phase velocities for frequencies between 2.5 Hz and 13.5 Hz and compared the results with the theoretical Rayleigh-wave-dispersion characteristics of both the fundamental and the first higher modes calculated from the PS logging data. Next, we tried to estimate the S -wave velocity structure to a depth of 43 m by fitting the theoretically calculated phase velocities to the experimental data, taking into consideration both the higher mode contributions as well as the fundamental mode. The theoretical dispersion characteristics were successfully fitted to the results analyzed by the ESAC method but not by the FK method. The estimated S -wave velocity structure from the ESAC method results was in good agreement with the PS logging profile. We also confirmed, using the model, that the S -wave transfer function due to vertical incidence coincided with that from the PS logging data. As a result of the study, we conclude that the ESAC method gives more accurate results than the FK method in determining the Rayleigh-wave phase velocity from records of short-period microtremors using arbitrarily shaped array configurations. The ESAC method can also provide a better estimate of the S -wave velocity structure and site amplification than the FK method.

Hydraulic tomography in fractured granite: Mizunami Underground Research site, Japan

Abstract: [1] Two large-scale cross-hole pumping tests were conducted at depths of 191–226 m and 662–706 m in deep boreholes at the Mizunami Underground Research Laboratory (MIU) construction site in central Japan During these two tests, induced groundwater responses were monitored at many observation intervals at various depths in different boreholes at the site We analyze the two cross-hole pumping tests using transient hydraulic tomography (THT) based on an efficient sequential successive linear estimator to compute the hydraulic conductivity (K) and specific storage (Ss) tomograms, as well as their uncertainties in three dimensions The equivalent K and Ss estimates obtained using asymptotic analysis treating the medium to be homogeneous served as the mean parameter estimates for the 3-D stochastic inverse modeling effort Results show several, distinct, high K and low Ss zones that are continuous over hundreds of meters, which appear to delineate fault zones and their connectivity The THT analysis of the tests also identified a low K zone which corresponds with a known fault zone trending NNW and has been found to compartmentalize groundwater flow at the site These results corroborate well with observed water level records, available fault information, and coseismic groundwater level responses during several large earthquakes The successful application of THT to cross-hole pumping tests conducted in fractured granite at this site suggests that THT is a promising approach to delineate large-scale K and Ss heterogeneities, fracture connectivity, and to quantify uncertainty of the estimated fields