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 Simulation of strong ground motions

1980 ◽  
Vol 70 (2) ◽  
pp. 617-630
Author(s):  
David M. Hadley ◽  
Donald V. Helmberger
Keyword(s):  
Ground Motions ◽  
Strike Slip ◽  
Peak Acceleration ◽  
Limited Data ◽  
Distance Curve ◽  
Data Set ◽  
Strong Ground Motions ◽  
Parkfield Earthquake ◽  
Large Earthquakes ◽  
Strong Ground

abstract The estimation of potential strong ground motions at short epicentral distances (Δ = 10 to 25 km) resulting from large earthquakes, M ≧ 6.5, generally requires extrapolation of a limited data set. The goal of this project has been to quantify the extrapolation through a simulation technique that relies heavily upon the more extensive data set from smaller magnitude earthquakes. The simulation utilizes the smaller events as Green's functions for the elements of a larger fault. Comparison of the simulated peak acceleration and duration with the data from the Parkfield earthquake is very good. Simulation of three earthquakes, M = 5.5, 6.5, and 7.0 indicate that the slope of the peak acceleration versus distance curve (Δ = 5 to 25 km) flattens, for strike-slip earthquakes, as the magnitude increases.

Long-Period Ground Motions Observed in the Northern Part of Kanto Basin, During the 2011 off the Pacific Coast of Tohoku Earthquake, Japan

2013 ◽  
Vol 8 (sp) ◽  
pp. 781-791 ◽  
Author(s):  
Seiji Tsuno ◽  
◽  
Andi Muhamad Pramatadie ◽  
Yadab P. Dhakal ◽  
Kosuke Chimoto ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Love Wave ◽  
Pacific Coast ◽  
Velocity Structure ◽  
Ground Motions ◽  
Tohoku Earthquake ◽  
S Wave ◽  
Long Period ◽  
The Pacific ◽  
Kanto Basin

During the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0), strong ground motions were observed at many seismic stations in the Tokyo Metropolitan Area located about 200 km away from the southern edge of the earthquake source fault. Large earthquake responses in high-rise buildings having long natural periods of several seconds were also observed. The largest ground responses for a period of 4 to 5 seconds were observed locally in Oyama (K-NET TCG012) and Koga (K-NET IBR009) on the border between Tochigi and Ibaraki Prefectures in the northern part of Kanto basin. Geophysical information in these areas was not accurate enough, however, to evaluate these ground motions. To understand S-wave velocity structures, we performed array microtremors observations at TCG012 seismic station in Oyama. We applied the Spatial Autocorrelation (SPAC) method to array microtremors data for vertical components. Rayleigh wave phase velocity from 0.3 to 1.6 km/s was obtained for a period of 0.25 to 3 seconds. We inverted phase velocity to a S-wave velocity structure reaching to bedrock at a depth of 1.6 km, using a Genetic Algorithm. The estimated structure explained the first peak of the H/V spectral ratio of microtremors well by the ellipticity of fundamentalmode Rayleigh wave. To evaluate long-period ground motions observed around Oyama during the main shock, we estimated earthquake ground motions by 1-D analysis, showing agreements with and the differences from those observed. As a result, velocity calculated at IBR008 located midway between the Tsukuba Mountains and Oyama, explained that observed for main phases and later phases. However, velocity calculated at TCG012 did not explain that observed for later phases. According to the emphasis of airy phases for group velocity of Love wave using the estimated S-wave velocity structure and the principal axis for later phases obtained by PCA corresponding to the vibration direction of Love wave propagating from the earthquake source fault and through the Tsukuba Mountains, long-period ground motions of a period of 3 to 5 seconds observed at TCG012 lasting for 200 seconds after the arrival of main phases, consist of Love wave.

scholarly journals Broadband Strong-Motion Prediction for Future Nankai-Trough Earthquakes Using Statistical Green’s Function Method and Subsequent Building Damage Evaluation

2021 ◽  
Vol 11 (15) ◽  
pp. 7041
Author(s):  
Baoyintu Baoyintu ◽  
Naren Mandula ◽  
Hiroshi Kawase
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Nankai Trough ◽  
Ground Motions ◽  
Building Damage ◽  
Steel Buildings ◽  
Ground Acceleration ◽  
Attenuation Relations ◽  
Strong Ground Motions ◽  
Strong Ground

We used the Green’s function summation method together with the randomly perturbed asperity sources to sum up broadband statistical Green’s functions of a moderate-size source and predict strong ground motions due to the expected M8.1 to 8.7 Nankai-Trough earthquakes along the southern coast of western Japan. We successfully simulated seismic intensity distributions similar to the past earthquakes and strong ground motions similar to the empirical attenuation relations of peak ground acceleration and velocity. Using these results, we predicted building damage by non-linear response analyses and find that at the regions close to the source, as well as regions with relatively thick, soft sediments such as the shoreline and alluvium valleys along the rivers, there is a possibility of severe damage regardless of the types of buildings. Moreover, the predicted damage ratios for buildings built before 1981 are much higher than those built after because of the significant code modifications in 1981. We also find that the damage ratio is highest for steel buildings, followed by wooden houses, and then reinforced concrete buildings.

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