Junji Kiyono

Simulation of stochastic waves in a non-homogeneous random field

Abstract Stochastic waves are simulated in a non-homogeneous field; layered media with irregular interfaces. Observed waves are specified at one or more points, and the proposed procedure simulates waves at arbitrary points for which no motion has been proposed, using only information from observed records. Stochastic waves are assumed to be composed of a deterministic component (trend wave) and a stochastic component (random wave). We propose a simple trend model that uses the Fourier spectrum of the observed wave. The kriging method is used for the optimum interpolation of random waves. According to the conditional simulation, random stochastic waves were generated on a non-homogeneous random field. The simulated waves are coincident with known time histories at specific points. To check the validity of the procedure developed, we calculated the waves in layered media with irregular interfaces using the discrete wave-number method and compared them to the waves simulated by our procedure. This procedure that includes the kriging technique provides an efficient means by which to simulate the stochastic waves of a non-homogeneous random field.

Designed microtremor array based actual measurement and analysis of strong ground motion at Palu city, Indonesia

In this study, we investigated the strong ground motion characteristics under Palu City, Indonesia. The shear wave velocity structures evaluated by eight microtremors measurement are the most applicable to determine the thickness of sediments and average shear wave velocity with Vs ≤ 300 m/s. Based on subsurface underground structure models identified, earthquake ground motion was estimated in the future Palu-Koro earthquake by using statistical green’s function method. The seismic microzonation parameters were carried out by considering several significant controlling factors on ground response at January 23, 2005 earthquake.

Seismic Microzonation of Mandalay City, Myanmar

Understanding the parameters of PGA (peak ground acceleration) is very important for seismic hazard mitigation and environmental planning in Mandalay City, Myanmar. In this study, fifty SPTs (Standard Penetration Tests) measurement data were collected in Mandalay City, for calculating average shear velocity Vs30, which will be used in seismic microzonation mapping. The shear wave velocity Vs30 of the top layer is Vs30 ≤ 220 m/s. The ground motion characteristic was estimated by means of the predominant periods and linear magnification factors obtained using the multiple reflection analysis. The highest potential zone of seismic hazard mostly locates the north western marginal part of Mandalay city, in the proximal portion to the dextral Sagaing fault.

Estimation of underground structure at Prambanan area, Yogyakarta, Indonesia

In this study, we investigated the underground structure at Prambanan area, Yogyakarta. We performed single observations of microtremor at 124 sites in Prambanan area. The results enabled us to estimate the site-dependent shaking characteristics of earthquake ground motion. We also conducted 2-site bore holes investigation to gain a representative determination of the soil condition of subsurface structures in Prambanan. From the SPT of borehole observations, the prambanan area corresponds to relatively soil condition with Vs ≤ 298 m/s, the predominant periods due to horizontal vertical ratios (HVSRs) are in the range of 0.48 to 1.19 s and the frequency are in the range of 0.95 to 1.92u2005Hz. By making these observations, we can obtain a relationship between the predominant periods, frequency and distribution of the first layer thickness of the sediment.

Probabilistic seismic hazard assessment for Nepal

Written history of great earthquakes in excess of magnitude M8 and recently identified 92 small faults around underlying big three fault systems parallel to the Himalayas show a high seismicity in Nepal. However, since faults are so closed that it is difficult to judge which earthquake belongs to which fault and even some of the faults do not hold earthquakes, the usual method of assigning the earthquakes to the nearest fault developing magnitude-frequency relationship is not applicable. Thus, an attempt has been made here to address the problem considering area sources with different densities at each location based upon historical earthquakes and faults which is real evidence of the seismicity of the region. Separate earthquake densities are calculated based upon historical earthquakes and maximum magnitudes of faults using the kernel estimation method which accounts the significance of both the number of earthquakes and size. Since there is no specific attenuation laws developed for the Himalayan region, five attenuation laws developed for seduction zone are selected and used, giving equal weight to all to minimize the uncertainties. Then, the probabilistic spectra for various return periods are calculated, compared with previous estimates and various aspects discussed.