scholarly journals Modeling of Deep Sedimentary Velocity Structure for Evaluati Broadband Strong Ground Motions: Site-Amplification Spectra in Osaka Sedimentary Basin

2006 ◽  
Vol 6 (4) ◽  
pp. 113-132 ◽  
Author(s):  
Ikuo CHO ◽  
Masato TSURUGI ◽  
Takao KAGAWA ◽  
Tomotaka IWATA
Keyword(s):  
Velocity Structure ◽  
Sedimentary Basin ◽  
Ground Motions ◽  
Site Amplification ◽  
Strong Ground Motions ◽  
Strong Ground

Nonlinear site amplification at CCHG observed by strong ground motions during the 2011 off the Pacific coast Tohoku earthquake

2015 ◽  
Author(s):  
Kohei Tanaka ◽  
Seiji Tsuno ◽  
Hiroaki Yamanaka ◽  
Kosuke Chimoto ◽  
Makoto Kamiyama ◽  
...  
Keyword(s):  
Pacific Coast ◽  
Ground Motions ◽  
Tohoku Earthquake ◽  
Site Amplification ◽  
Strong Ground Motions ◽  
The Pacific ◽  
Strong Ground

scholarly journals Nonlinearity, liquefaction, and velocity variation of soft soil layers in Port Island, Kobe, during the Hyogo-ken Nanbu earthquake

1997 ◽  
Vol 87 (5) ◽  
pp. 1244-1258 ◽  
Author(s):  
Jorge Aguirre ◽  
Kojiro Irikura
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Ground Motions ◽  
Peak Acceleration ◽  
Spectral Ratios ◽  
S Wave ◽  
Strong Ground Motions ◽  
Before And After ◽  
Different Depths ◽  
Strong Ground

Abstract Clear nonlinear behavior is analyzed from the acceleration records of the 1995 Hyogo-ken Nanbu earthquake at Port Island, Kobe. From four triaxial instruments placed at four different depths, the surficial effects during strong ground motions were compared with those during weak motions before and after the mainshock. We used a spectral ratio technique and a nonlinear inversion for velocity structure to analyze the data. From the spectral analysis, we observed a large variation of the spectral ratios between the surface and different depths during the strong ground motions and during the liquefied state. The spectral ratios after the mainshock (i.e., after the liquefied state) are different from those before the mainshock. The peak frequencies in the spectral ratios after the mainshock are shifted to lower frequencies with respect to those in the spectral ratios before the mainshock. We inverted the S-wave velocities using a genetic algorithm technique to determine the velocity structure before, during, and after the mainshock. The S-wave velocity structure before and after the mainshock was found to be different. Specifically, the S-wave velocity of the second layer (5 m to 16 m depth) after the mainshock was 20% lower than before. Our analysis shows that the liquefied state remains at least 3 hr after the mainshock but no more than 24 hr. The rigidity of the soil decreased close to zero when liquefaction happened and later increases gradually following a trend that resembles a consolidation curve. The strong influence of nonlinearity during the mainshock yielded a big reduction of the horizontal surface ground motions, so that the observed horizontal peak acceleration was only about 25% of the peak acceleration expected from the linear theory. However, the nonlinear effects in the vertical peak acceleration were not significant.

scholarly journals Analysis of Site Amplification and Nonlinear Response Based on Ground Motion Records at MYGH10 Station in Japan

2021 ◽  
Author(s):  
Shiliang Zhang ◽  
Dongwang Tao ◽  
Quancai Xie ◽  
Qiang Ma ◽  
Fuchen Wang
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Ground Motions ◽  
Spectral Ratio ◽  
Site Amplification ◽  
Predominant Frequency ◽  
Strong Ground Motions ◽  
Ground Motion Records ◽  
Site Amplification Factor ◽  
Strong Ground

Abstract Strong horizontal ground motions with the peak ground acceleration (PGA) larger than 1400 gal were observed at Yamamoto (MYGH10) station during the February 2021 Mj 7.3 off the east coast of Honshu, Japan, Fukushima earthquake. Firstly, in this paper, we discussed and verified the theoretical assumptions of the “Nakamura” method under weak and strong ground motions. The site amplification factor of the MYGH10 station was estimated using the surface horizontal-vertical spectral ratio (HVSR) and the surface-to-borehole spectral ratio (SBSR), and the corrected HVSRC, respectively. Meanwhile, the reasons for underestimating the site amplification factor when using HVSR were explained. The vertical amplification phenomenon of seismic P-wave in the high-frequency band was analysed under weak and strong ground motions. Secondly, we utilized HVSR, SBSR, and theoretical transfer function (TTF) based on the 1D wave propagation theory to study the nonlinear site response of MYGH10 station under the mainshock of the Fukushima earthquake and the historically weak and strong ground motions, respectively. The changes in frequencies and amplitudes of the spectral ratio curves when nonlinearities were occurring at the site were analysed and compared using the spectra ratio curves of weak ground motion records and TTF as references. Finally, the recovery of the site after strong nonlinearity was also evaluated by comparing the spectral ratio curves of aftershocks records. We found that the most significant amplification factor of the site increased from 7 to more than 10, and the predominant frequency decreased from 10 Hz to 3.8 Hz under the mainshock of the Fukushima earthquake. The predominant frequency returned to the previous value within three days after the mainshock, but the amplification factor did not.

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