Ohsaki Research Institute Inc.

Japan

Ohsaki Research Institute Inc.

Japan
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Satoh T.,Ohsaki Research Institute Inc. | Okawa I.,Japan Building Research Institute | Nishikawa T.,Tokyo Metroplitan University | Sato T.,Shimizu Corporation | Seki M.,Japan Building Disaster Prevention Association
Journal of Structural and Construction Engineering | Year: 2010

We develop empirical regression relations for estimating waveforms of horizontal and vertical ground motions in a period range of 0.1 tol0 seconds caused by subduction-zone and crustal earthquakes using many strong motion records all in Japan. The relations are provided for 5 % and 1 % damped acceleration response spectra, energy spectrum, average of group delay time, and standard deviation of group delay time. The waveforms with site-specific amplification and phase spectra are easily calculated by the empirical relations using the outer-fault parameters, rupture starting points, delay time among rupture starting points, and the location of the strong motion stations in interest. We show that waveforms calculated by the empirical relations for the hypothetical Nankai earthquake are consistent with waveforms calculated by the theoretical method using three dimensional structure model and inner-fault parameters as well as outer-fault parameters in previous studies.


Satoh T.,Ohsaki Research Institute Inc. | Okawa I.,Japan Building Research Institute | Nishikawa T.,Tokyo Metroplitan University | Sato T.,Shimizu Corporation
Journal of Structural and Construction Engineering | Year: 2011

We present a new empirical model to spatially interpolate amplification factors of 5 % damped acceleration response spectra obtained at strong motion stations at intervals of about 10 to 20 km for periods ranging from 0.5 to 10 s. The predictor variable is Tz3.2 which is the propagation time of S wave from the seismic bedrock to the engineering bedrock calculated by velocity structure just beneath the station extracted from three-dimensional model with a grid spacing of about 1km. The logarithm of the amplification factors in the Kanto basin, the Nobi basin, and the Osaka basin are modeled by bi-linear regression lines using the Tz3.2. We also interpret the bi-linear regression lines by medium response of surface waves.


Satoh T.,Ohsaki Research Institute Inc. | Okawa I.,Japan Building Research Institute | Sato T.,Shimizu Corporation | Tohdo M.,Ohsaki Research Institute Inc. | Nishikawa T.,Tokyo Metroplitan University
Journal of Structural and Construction Engineering | Year: 2014

Long-period ground motions for the Nankai Trough mega-earthquakes are predicted using our empirical relations for 5 % damped acceleration response spectra and group delay time. The predicted waves in the period rage of 0.1 to 10 seconds for the Tonankai earthquake (Mw8.1), the Nankai earthquake (Mw8.4), and the hypothetical mega-earthquake (Mw9.0) are consistent with the previous waves predicted by the other methods if the variations of data and the difference of the methods are taken into account. We also develop empirical models to interpolate site factors obtained at strong motion stations at intervals of about 10 to 20 km in the Kanto basin, the Nobi basin, and the Osaka basin and apply the models for these predictions.


Oana A.,Shimizu Corporation | Dan K.,Shimizu Corporation | Tohdo M.,Ohsaki Research Institute Inc. | Ishii T.,Shimizu Corporation | And 2 more authors.
Journal of Structural and Construction Engineering | Year: 2015

We proposed a procedure for evaluating fault parameters taking into account of heterogeneous dynamic stress drops on the asperities, and calculated strong ground motions. We compiled the stress drop data on the asperities of earthquakes caused by strike-slip faults and reverse faults. In order to establish fault models for strong motion predictions, we applied the log-normal distribution to the stress drop data, and examined a procedure for assigning heterogeneous dynamic stress drops to each asperity by using the obtained log-normal distributions. The strong ground motions predicted by using this proposed procedure had larger variations of the peak ground accelerations and velocities than those with uniform dynamic stress drops on the asperities, while the averages were almost same.


Dan K.,Ohsaki Research Institute Inc. | Ju D.,Ohsaki Research Institute Inc. | Shimazu N.,Ohsaki Research Institute Inc. | Irie K.,Ohsaki Research Institute Inc.
Journal of Structural and Construction Engineering | Year: 2012

We evaluated the fault parameters of asperity models for inland earthquakes caused by long strike-slip faults based on the procedure proposed by Dan et al. (2011)1), and simulated strong ground motions by these asperity models. The models had a constant dynamic stress drop averaged over the entire fault of 34 bars and that on the asperities of 122 bars. We presented . ve models with the fault length of 25 km, 50 km, 100 km, 200 km, and 400 km, and simulated strong ground motions from the three models with the fault length of 50 km, 100 km, and 400 km. The simulated motions were consistent with the records of the 2000 Tottori-Ken Seibu, Japan, earthquake, and the 2002 Denali, Alaska, earthquake as well as the attenuation model of peak accelerations and peak velocities proposed by Si and Midorikawa (1999)2). These results veri. ed the procedure proposed by Dan et al. (2011)1) for evaluating fault parameters of asperity models.


Dan K.,Ohsaki Research Institute Inc. | Irie K.,Ohsaki Research Institute Inc. | Ju D.,Ohsaki Research Institute Inc. | Shimazu N.,Ohsaki Research Institute Inc. | Torita H.,Ohsaki Research Institute Inc.
Journal of Structural and Construction Engineering | Year: 2015

The asperity model is the most popular fault model for predicting ground motions in Japan (Headquarters of Earthquake Research Promotion, 2005). The procedure for evaluating fault parameters of the asperity model was compiled as a recipe by Irikura and Miyake (2001) and so on. However, it is well known that this procedure gives unrealistic fault parameters for inland earthquakes with very long faults (Architectural Institute of Japan, 2008). Dan et al. (2011) solved this problem for very long strike-slip faults. Hence, in this paper, we tried to solve the problem for very long reverse faults. We adopted the evaluation formula of averaged dynamic stress drops obtained by Irie et al. (2013) for surface ruptured reverse faults 15 to 300 km long, because the evaluation formula of the averaged static stress drops for circular cracks, commonly adopted in existing procedures, could not be applied to surface ruptured faults or long faults. The averaged dynamic stress drop was estimated to be 24 bars from the data of the ruptured areas and the seismic moments of actual earthquakes, and the dynamic stress drop on the asperities was estimated to be 187 bars from the data of the short-period levels and the seismic moments of actual earthquakes. These results led that the asperity areas were 11 % of the entire ruptured areas. Then, we proposed a new procedure for evaluating the fault parameters of the asperity model for reverse faults. This new procedure has a feature that the length of an active fault and the top depth and the bottom depth of the seismogenic layer are given from geological survey and seismological investigation as the existing procedures. Several asperity models were demonstrated for the fault lengths of 25 km, 50 km, 100 km, 200 km, and 400 km. At last, we simulated strong ground motions by the stochastic Green's function method based on the demonstrated asperity models for the fault lengths of 50 km, 100 km, and 400 km. The simulated strong ground motions showed good agreement with the peak ground accelerations and the peak ground velocities by empirical relations of Si and Midorikawa (1999) as well as the velocity response spectra of the 2004 Niigata-Chuetsu, Japan, earthquake (MJ 6.8) and the peak ground accelerations and peak ground velocities of the 2008 Wenchuan, China, earthquake (MW 7.9). These results validated the new procedure for predicting ground motions from inland earthquakes caused by very long reverse faults.


Satoh T.,Ohsaki Research Institute Inc.
Journal of Structural and Construction Engineering | Year: 2010

Empirical relations between short-period source spectra and seismic moment for dip-slip and strike-slip crustal earthquakes in Japan, ranging moment magnitude from 5.7 to 6.9, are developed by spectral inversion method using near-fault strong motion records. The short-period source spectrum A for dip-slip earthquakes is 1.45 times of A by Dan et al.'s empirical relation for crustal earthquakes in the world. The A for strike-slip earthquakes is 0.64 times of A by Dan et al.'s relation. The A calculated from previous source models estimated by empirical Green's function method has the similar trend. The combined asperity area of the previous source models has no differences between dip-slip and strike-slip crustal earthquakes and is 0.8 times of Somerville et al. 's relation for crustal earthquakes in the world. On the other hand, the A for interplate earthquakes in eastern Japan, ranging moment magnitude from 6.6 to 8.2, estimated by spectral inversion method in previous studies is found to be 1.63 times of A by Dan et al.'s relation.


Satoh T.,Ohsaki Research Institute Inc.
Journal of Structural and Construction Engineering | Year: 2010

The Q value and short period source spectra of the 2009 Suruga bay earthquake ({6.5) and its aftershocks are estimated using spectral inversion method. Then the source model composed of two strong motion generation areas (SMGAs) are estimated using the empirical Green's function method. The estimated Q value near the source region is modeled as 30fDM, that is, f is frequency The short period source spectrum of the main shock is the largest among previous intmslab earthquakes occulTed in the Philippine Sea plate and larger than the average value for intraslab earthquakes oceulTed in the Pacific Sea plate. The stress drop and the total area of SMGAs ate estimated to be 751 bar and 18 km2, respectively The stress drop of SMGAs is larger than the empirical scaling law for custal earthquakes and big intractable earthquakes in the Philippine Sea plate. The total area SMGAs is smaller than the empirical scaling law for crystal earthquakes.


Dan K.,Ohsaki Research Institute Inc. | Shimazu N.,Ohsaki Research Institute Inc. | Muto M.,Ohsaki Research Institute Inc.
Journal of Structural and Construction Engineering | Year: 2010

Many multi-crack models have been obtained from strong-motion records as the fault models for recent damaging earthquakes. However, these multi-crack models do not specify the total seismic moment or the magnitude of the earthquakes. Neither do they have a consistent physical basis between the slip and the stress drop, because no slip is assumed on the background of the fault for calculating the stress drop on the cracks while small amount of the slip actually exists on the background. Hence, we proposed a procedure for transforming the multi-crack models into the asperity models. The asperity models specify the seismic moment and have a consistent physical basis. They are also easy to apply to fault models for larger scenario earthquakes. As an example, we transformed the multi-crack model for the 2005 Fukuoka-Ken Seiho-Oki earthquake (M J 7.0) into an asperity model, and then showed three different asperity models to predict strong motions for scenario earthquakes twice larger than the Fukuoka-Ken Seiho-Oki earthquake.


Dan K.,Ohsaki Research Institute Inc. | Ju D.,Ohsaki Research Institute Inc. | Muto M.,Ohsaki Research Institute Inc.
Journal of Structural and Construction Engineering | Year: 2010

Short active faults observed on the ground surface have been supposed to indicate longer subsurface faults in the seismogenic layer. However, no concrete procedures have been proposed so far for modeling the subsurface faults for predicting strong ground motions. Hence, we surveyed several important research papers, and proposed a procedure for modeling the subsurface faults. Here, the seismic moment M 0 of 7.5 × 10 25 dyne·cm was assumed as the minimum size of the source for the case that any short active faults were observed on the surface. The modeling procedure was based on the asperity model, that was adopted by the Headquaters of Earthquake Research Promotion (2005) in Japan. Five main fault parameters of the area of the entire fault S, the averaged stress drop Δσ, the area of the asperities S asp the stress drop on the asperities Δσ asp, and the short-period level A were determined by the two theoretical relationships and the three empirical relationships among the six main fault parameters including the seismic moment M 0.

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