Table 2 - uploaded by Hiroaki Yamanaka
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Source publication
Observation of aftershocks of the 2003 Tokachi-Oki earthquake was conducted in the southern part of the Tokachi basin in Hokkaido, Japan for estimation of local site effects. We installed accelerographs at 12 sites in Chokubetsu, Toyokoro, and Taiki areas, where large strong motion records were obtained during the main shock at stations of the K-NE...
Contexts in source publication
Context 1
... of S-wave spectra at CBT1 and CBT3 to that at CBT2 were calculated from averaging the ratios for Period (s) Fig. 7. Ratios of spectra of aftershocks at stations of CBT1 and CBT3 to that at reference site of CBT2. The ratios are calculated from average of S-wave spectra of all the records from the events in Table 2. the events in Table 2. We used root-mean square of the two horizontal spectra to calculate the spectral ratios. ...
Context 2
... of S-wave spectra at CBT1 and CBT3 to that at CBT2 were calculated from averaging the ratios for Period (s) Fig. 7. Ratios of spectra of aftershocks at stations of CBT1 and CBT3 to that at reference site of CBT2. The ratios are calculated from average of S-wave spectra of all the records from the events in Table 2. the events in Table 2. We used root-mean square of the two horizontal spectra to calculate the spectral ratios. ...
Context 3
... (s) Fig. 9. Ratios of spectra of aftershocks at stations of TYK1 to TYK4 and TYK6 to that at reference site of TYK5. The ratios are calculated from average of S-wave spectra of all the records from the events in Table 2. ...
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... of spectra of aftershocks at stations of TIK2 and TIK3 to that at reference site of TIK1. The ratios are calculated from average of S-wave spectra of all the records from the events in Table 2. having an S-wave velocity of 130 m/s. We, next, discuss the site amplification factors in the Toyokoro area. ...
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Modification in the semi-empirical technique for the simulation of strong ground motion has been introduced to incorporate the strong motion generation areas (SMGA) in the modeled rupture plane. Strong motion generation areas identified within the rupture plane of the Tohoku earthquake of March 11, 2011 (M
w = 9.0), have been modeled using this mod...
In this study, the illumination of an observation site from the source is assumed to be produced only by incident plane waves. The average of normalized ground motion spectral densities will then depends only on depth and a one dimensional description of wave propagation for a diffuse field of ground motions can be applied. Thus, the imaginary part...
Citations
... The observed Sv at the K-NET and KiK-net (borehole) stations were computed after applying a band-pass filter at 2-20 s and are plotted on the maps for comparison. It should be noted that the observed Sv at the K-NET stations include the effects of surface layers and may have been affected by nonlinear site response because the data are recorded on the ground surface, although we did not use stations where distinctive nonlinear site responses have been reported by several papers (e.g., Yamanaka et al. 2004;Morikawa et al. 2006). In the southeastern region of Hokkaido, Model H3 generally more closely agrees with the observations than Model C, especially at periods of 2, 3, and 5 s, at which the large values of Sv along the southeastern coast of Hokkaido around Yufutsu, Tokachi, and Kushiro Plains (locations of the plains are shown in Fig. 2) are well reproduced by Model H3. ...
In this study, a method for simulating the ground motion of megathrust earthquakes at periods of approximately 2 s and longer was validated by using the characterized source model combined with multi-scale spatial heterogeneity. Source models for the M W 8.3, 2003 Tokachi-oki earthquake were constructed, and ground motion simulations were conducted to test their performance. First, a characterized source model was generated based on a source model obtained from waveform inversion analysis. Then, multi-scale heterogeneity was added to the spatial distribution of several source parameters to yield a heterogeneous source model. An investigation of the Fourier spectra and 5 % damped velocity response spectra of the simulated and observed ground motions demonstrated that adding multi-scale heterogeneity to the spatial distributions of the slip, rupture velocity, and rake angle of the characterized source model is an effective method for constructing a source model that explains the ground motion at periods of 2-20 s. It was also revealed how the complexity of the parameters affects the resulting ground motion. The complexity of the rupture velocity had the largest influence among the three parameters.
... However, a major disadvantage of this assumption is that nonlinear site responses are not considered. Therefore, stations along the Pacific coast of Hokkaido, where distinctive nonlinear site responses are detected during the strong shaking of the mainshock (e.g., Yamanaka et al., 2004;Morikawa et al., 2006), are excluded in our analysis. ...
We present a new approach for broadband ground-motion simulation that is a combination of high-frequency (HF, f > 0:5 Hz) and low-frequency (LF, f < 0:5 Hz) ground-motion simulations. In this method, the LF ground motion is first computed by a deterministic approach based on a velocity model and a source model. Then, the HF acceleration envelopes are computed by multiplying the LF envelopes by envelope ratio functions (ERFs), which are defined as the empirical relationships between the characteristics of envelopes of different frequency bands. We apply the method to the 2003 Tokachi-Oki, Japan, earthquake (Mw 8.3). The LF ground motion is computed by a finite-difference method with a 3D velocity model and a finite-fault slip model. Because of the complicated rupture process of the earthquake, the fault is divided into subfaults that can be considered as smaller earthquakes. ERFs are estimated by investigating the ground-motion data of moderate-size aftershocks (5:4 ≤ Mw ≤ 6:6) for each station. The HF ground motions are simulated using the LF ground motion and the ERFs. Seismograms of all frequency bands are summed to give a time series of broadband (0.05–16 Hz) ground motion.We find that our method yields realistic broadband ground motion, in terms of the acceleration envelope, velocity waveform, and Fourier amplitude spectrum. Comparing the HF waveforms with those computed by the stochastic Green’s function method (SGFM), we find that the performance of our method is better than that of the SGFM under the condition that LF waveforms are appropriately computed. The proposed method has the potential to be used as a practical method for broadband ground-motion prediction incorporating the effects of a 3D velocity model and a finite-source model.
... Seismic motions underground have been studied by many authors since the pioneering study of Kanai and Tanaka (1951) in the Hitachi mine in Japan, which documented amplification of seismic wave motions on the surface relative to those underground (up to 450 m). Numerous experiments involving borehole in situ observations made at different levels within a soil column and in the bedrock below have been conducted to improve our understanding of the effects of a shallow soil column on ground motion, and to quantify the observed amplification and attenuation effects of near-surface formations to incident seismic motion (Blakeslee and Malin, 1991; Fukushima et al., 1995; S. Kinoshita, 1999 S. Kinoshita, , 2008 Graizer et al., 200; Okada et al., 2004; Yamanaka et al., 2004; Iida et al., 2005 and many others). Site response studies using deep underground records under conditions similar to those of the PUPS experiment in the Gran Sasso Massif in Abruzzo in Central Italy (1.4 km depth) (De Luca et al., 1998) and in the Tangshan Area in China (0.8 km) (Matsunami et al., 2003) also have shown that the ground motion intensity at depth is less than that at ground surface. ...
We compare signals recorded on hard-rock seismographic stations in Sudbury, Ontario to those recorded in caverns below the surface stations, in the Sudbury Neutrino Observatory. Signals from shallow local events show strong apparent amplification of ground motion observed on the surface relative to those recorded at depths of 1.4 to 2 km; the amplification peaks near 2 Hz, where it is on average a factor of three to five. The peak narrows, decreases in amplitude, and shifts towards lower frequencies (0.8-1 Hz) for regional and teleseismic events. The peak in apparent amplification for the local events is attributed to a strong Rg phase from shallow events at close distances. The frequency shift and decay of the amplitude of this peak for more distant events reflects the rapidly-diminishing influence of the higher-frequency components of this phase with distance, coupled with the increasing importance of shear-wave phases.
... A strong motion by the 2003 Tokachi-Oki Earthquake (M W 8.3, 25/09/2003) is recorded at station IBUH03 of KiK-net. There are several reports indicating the change in site amplification just after these strong motions [Yamazoe et al., 2004;Yamanaka et al., 2004]. Hereafter, we refer to the earthquakes occurred before and after the mainshock as foreshocks and aftershocks, respectively, even though they are not correct in the strict sense of the words. ...
The spectral ratios of coda waves of local earthquakes have been often used as measures of relative amplification factors of different sites. Applying this method to coda waves registered by seismometers installed on the surface and at the bottom of a borehole, we succeeded in stably measuring the temporal change in site response associated with the occurrence of a large earthquake strong motion. A remarkable drop of coda spectral ratio and a shift of the peak frequency were observed during strong shake at two sites by the 2000 Western Tottori Earthquake and at a site by the 2003 Tokachi-Oki Earthquake in Japan. The reduction of the peak frequency reached 30-70% at all the sites. After that, the peak frequency logarithmically recovered to the value before the strong motions for a few years at two sites, whereas the other one quickly recovered in a few tens of minutes.
... High quality data produced by the dense K-NET and KiKnet are providing a plenty of seeds for interesting researches. For example, in the special issue of Earth, Planets and Space for the 2003 Tokachi-oki earthquake, five papers are using K-NET and KiK-net data to discuss the source process or local site effects in the source region (Yagi, 2004;Honda et al., 2004;Kamae and Kawabe, 2004;Koketsu et al., 2004;Yamanaka et al., 2004). ...
After the disastrous 1995 Kobe earthquake, a new national project has started to drastically improve seismic observation system in Japan. A large number of strong-motion, high-sensitivity, and broadband seismographs were installed to construct dense and uniform networks covering the whole of Japan. The new high-sensitivity seismograph network consisting of 696 stations is called Hi-net, while the broadband seismograph network consisting of 71 stations is called F-net. At most of Hi-net stations strong-motion seismographs are also equipped both at depth and the ground surface. The network of these 659 stations with an uphole/downhole pair of strong-motion seismographs is called KiK-net, while another network consisting of 1034 strong-motion seismographs installed at the ground surface is called K-NET. Here, all the station numbers are as of April 2003. High-sensitivity data from Hi-net and pre-existing seismic networks operated by various institutions have been transmitted to and processed by the Japan
Serious damage due to ground liquefaction occurred in Urayasu City, located in the coastal area around Tokyo Bay, during to the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0). In particular, extensive liquefaction was observed in the Imagawa District of Urayasu City. In order to investigate the mechanism of damage and to establish appropriate countermeasures, it is very important to evaluate the strong ground motion in the Imagawa District. For this purpose, aftershock observations and microtremor measurements were carried out in and around the Imagawa District. Then, site effects in the Imagawa District were evaluated based on the microtremor H/V spectral ratios and the aftershock records.
Detailed analysis was conducted for the recorded mainshock across the country during the 21 May 2003 Boumerdes, Algeria earthquake. A remarkable difference has been recorded between neighbour stations. Since local site conditions have a significant effect on the ground motions, and hence on the damage distribution caused by the earthquake, microtremor survey was conducted at several sites of seismic observation stations. In this study, a particular attention is paid to 4 seismic network stations located in the most affected area between Algiers and Boumerdes provinces. Using the microtremor records and the strong motion records from five stations, the effect of soil condition on seismic motion is investigated and the damage distribution caused by this eventis explained. The results from this study show that in some stations, the recorded high PGA values were influenced by high-frequency contents. However, in other stations, soil amplification is considered to be responsible for high PGValues. Hence, in order to conduct a further engineering and seismological study, it is highly recommended to conduct an investigation to identify the local soil profile at the seismic stations.
