Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

1D velocity profiles at a strong motion station in the northern part of the Kumamoto plain, Japan, were submitted in Step-1 of the blind prediction exercise of strong ground motions in the sixth international symposium on effects of surface geology on seismic motion (ESG6). Individual participants were requested to estimate a 1D S-wave velocity profile of sedimentary layers from the given data obtained by microtremor array explorations and surface-wave explorations at the site. This paper reports the target site, methods used by the individual participants, and the submitted results. More than half of the participants estimated the phase velocities of the Rayleigh-wave in the frequency range from 0.53 to 29.8 Hz. The statistical analysis of the phase velocity dispersion curves indicates that the standard deviation was below 40 m/s at the frequencies above 3.4 Hz, and it was below 20 m/s above 20 Hz. The S-wave velocity profiles are also similar to a depth of 20 m. The standard deviation was below 45 m/s. The average S-wave velocity in the top 30 m from the surface is 207.3 ± 60.7 m/s for the submitted profiles. The large variation is related to the introduction of the near-surface low velocity layers. The large variation of the S-wave velocities was found in the deep part. The average S-wave velocity at a depth of 1500 m was 2674 m/s with the standard deviation of 786 m/s. We compared 1D amplifications for the submitted profiles. Common peaks can be identified at 0.3–0.4 Hz and 1–2 Hz, excluding two teams. However, the amplifications vary much in the frequency range higher than 4 Hz. Through the experiment, it was found that the dispersion curves and the shallow S-wave velocity structures are estimated with a low standard deviation among the participants. Further development of the techniques for deep S-wave velocity profiling was found to be required.

Graphical Abstract

DOI： 10.1186/s40623-023-01842-3

researchmap

Other Link： https://link.springer.com/article/10.1186/s40623-023-01842-3/fulltext.html

Authorship：Lead author,　Corresponding author  

DOI： 10.3124/segj.76.22

researchmap

Authorship：Lead author,　Corresponding author  

DOI： 10.1007/s10950-022-10072-1

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Society of Exploration Geophysicists of Japan  

DOI： 10.3124/segj.75.98

researchmap

DOI： 10.3124/segj.76.22

researchmap

DOI： 10.3124/segj.75.89

researchmap

Authorship：Lead author,　Corresponding author  

DOI： 10.3124/segj.75.56

researchmap

Publishing type：Research paper (international conference proceedings)   Publisher：Society of Exploration Geophysicists and Society of Exploration Geophysicists of Japan  

DOI： 10.1190/segj2021-026.1

researchmap

Authorship：Lead author,　Corresponding author  

DOI： 10.3389/feart.2021.681199

researchmap

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Society of Exploration Geophysicists of Japan  

DOI： 10.3124/segj.74.49

researchmap

Authorship：Lead author,　Corresponding author  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：Japanese   Publisher：JAPAN ASSOCIATION FOR EARTHQUAKE ENGINEERING  

During the 2011 Tohoku Earthquake, the peak ground accerelation (PGA) with high value of above 1000 cm/s2 was observed at K-NET Hitachi and K-NET Hokota, located in the coastal region of Ibaraki prefecture which is close to the southern edge of the fault, and the PGA close to 1000 cm/s2 was also observed at KiK-net Iwase, located in the boundary between Ibaraki and Tochigi prefecture. However, few records were observed in the area between these stations, referred to as Higashi-Ibaraki Terrace. Moreover, we have less information about subsurface structures in the area. Accordingly we performed aftershock observation of the Tohoku Earthquake and microtremor measurements to evaluate ground motion characteristics in the area. Aftershock records mostly show large accelerations in the eastern part of the terrace, but it is also large at the middle of the terrace. We then estimated the S-wave velocity profiles from microtremor explorations and we found that the shallow soil layers are deep in the middle of the terrace, while seismic bedrock is deep in the eastern part. Thus, the soil amplification has a peak at short period in the western part of the terrace, while it has a peak at about 1 second in the middle of the terrace. It has two peaks at short and long periods in the eastern part due to the shallow and deep soil structures. These amplifications showed similarity with the spectral ratios of the aftershocks.

DOI： 10.5610/jaee.16.4_142

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：Japanese   Publisher：Architectural Institute of Japan  

The 2014 Northern Nagano Earthquake, occurred on 22 November 2014, caused the heavy damage to wooden houses especially in the Horinouchi and Mikkaichiba districts in Hakuba, Nagano prefecture, even though the maximum intensity was 6 lower observed during the event. However, we do not know the feature of the strong ground motion in the districts because of no availability of mainshock records. We therefore performed the aftershocks and the microtremor observations around the districts to evaluate the local site effect. The observed ground motions of aftershocks exhibit a variety within several km, such that the S-wave at periods of 0.5-1.0 s dominate in Horinouchi and Mikkaichiba, while the aftershock records are relatively small at K-NET Hakuba. The S-wave velocity structure was revealed with microremor exploration and we found that the Horinouchi district has the shallow soft soil with a depth of about 30 m, while the shallow soil is stiff at K-NET Hakuba. An average S-wave velocity in the top of 30 m depth shows a correlation with the seismic intensity and the amplification. The comparison of the spectral ratios of the aftershocks indicates that the ground motion at periods of 0.5-1.0 s is amplified due to the shallow soft soil in Horinouchi and Mikkaichiba. We observed the seismic intensity was large with an increase of about 1 in Horinouchi compared to the surrounding area. However, the effects of deep structure must be also considered in understanding of ground motion features since the observed amplification factor is larger than the estimation.

DOI： 10.3130/aijs.81.51

CiNii Books

CiNii Research

researchmap

Other Link： https://www.aij.or.jp/paper/detail.html?productId=416988

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Publisher：The Society of Exploration Geophysicists of Japan  

&nbsp;&nbsp;Recently, Independent Component Analysis (ICA) has been studied and developed as a new method for multidimensional signal processing in many fields. The ability to detect a certain sound among plural sounds is called the Cocktail-party effect, which is well known as the issue for blind signal separation in acoustics. ICA has been applied to the separation for sounds/biomedical signals and an image processing in the engineering. However, there are not many applications of ICA in fields of exploration geophysics and seismology. To identify noise excited by cars and trains included in seismic data and to separate earthquake ground motions by aftershocks occurred simultaneously during large earthquakes are the issue for blind signal separation; therefore, the development of the Cocktail-party effect is expected in geophysical and seismological fields. As to the separation problem of railway-induced ground vibration mixing in seismic data, in this study, we investigated the waveform separation of earthquake ground motions and railway-induced ground vibrations by ICA, through numerical experiments used the observed data.<br> &nbsp;&nbsp;At first, we applied ICA to synthetic waveforms mixed earthquake ground motions and railway-induced ground motions spatially without time lag under the condition of BSS, to separate the original signals from those synthetic waveforms. As a result, the earthquake ground motions and the railway-induced ground motions were well separated. And, in the case of distance ratio of 0.99 for two stations from a railway, the earthquake ground motions and the railway-induced ground motions were also well separated. Secondary, we applied ICA to waveforms mixed the observed earthquake ground motions and railway-induced ground motions. As a result, the earthquake ground motions and railway-induced ground motions separated were in good agreement with those observed, especially in the frequency range of 0.5 to 30Hz for the earthquake ground motions. Kurtosis which is the fourth-order cumulant of high order statistics for earthquake ground motions and railway-induced ground motions is large and those frequency distributions are in a shape of super-Gaussian type; therefore, we suggested that ICA is qualified for the separation problem of earthquake ground motions and railway-induced ground motions.<br>

DOI： 10.3124/segj.68.39

CiNii Books

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English  

researchmap

Language：Japanese   Publisher：Japan Society of Civil Engineers  

At present, the train operation control during earthquakes is implemented based on the earthquake motions observed on the ground surface along the railway line. To operate the trains during earthquakes adequately, the consideration of the structural seismic responses as well as earthquake ground motions is necessary. In this study, we estimated S-wave velocity structures and structural vibration characteristics using microtremore data along the model railway. And we evaluated earthquake motions not only on the ground surface but also on the structures along the railway line, using the seismic data observed at a reference site. As a result, the earthquake motions estimated are good correlations with those observed. Furthermore, we evaluated the amplification factors of the subsurface structures and the railway structures, using the earthquake motions estimated on the ground surface and the structures. These information can be applied to the judgment of train operation control. And also, it shows the week points of railway structures in which the seismic retrofit are needed before earthquakes and safety inspections are required right after earthquakes.

DOI： 10.2208/jscejseee.71.87

researchmap

Language：Japanese   Publisher：The Society of Exploration Geophysicists of Japan  

In case that strong ground force affects railway facilities during earthquakes, the reduction of the safety performance of railway structures and running vehicle is concerned. When strong ground motions are observed, railway operators stop trains as soon as possible to secure the safety of trains. After the operator stop trains, a cautious inspection patrol along the railway section following the rule decided in advance is implemented. After the safety of railway facilities are ensured, the train operation is resumed. To confirm visually the damage of railway facilities and deformation of railway tracks in the inspection, it may take a lot of time. To comprehend exactly the characteristics of earthquake ground motions along the railway line, therefore, the rapid evaluation of the earthquake ground motions are strongly required not only at the points where the seismographs are installed but also at the other points on the railway line.<br> We proposed the method for estimating the subsurface velocity structures and earthquake ground motions along a railway line. In this study, we tried to apply the method to a railway embankment section in the closed Takachiho railway line, of which length is approximately 600m. The adopted section consists of an embankment in a valley, ridge in an excavation and other embankment in a valley. We installed the seismographs at two embankment sites and an excavation site. At first, we estimated S-wave velocity structures at two embankment sites, using the geophysical exploration such as surface wave exploration and array microtremor survey. Secondly, we estimated the S-wave velocity structures along the railway section using the H/V spectral ratios obtained by the high-dense microtremor measurement based on the S-wave velocity structures estimated. Finally, we estimated the earthquake ground motions along the closed Takachiho railway section by the one-dimensional multiple reflection theory using an observed seismic motion at site of the excavation section. We confirmed the validity of the S-wave velocity structures and earthquake ground motions estimated by the proposed method, through the agreements of the observations and estimations along the railway section.<br>

DOI： 10.3124/segj.68.91

CiNii Books

researchmap

Language：Japanese   Publisher：The Society of Exploration Geophysicists of Japan  

&nbsp;&nbsp;When the safety of railway facilities and running vehicles are threatened by large shakings of ground motions during earthquakes, railway operators stop trains as soon as possible. After the safety of train operation are ensured by a cautious inspection patrol along the railway section following the rule decided in advance, the train operation is resumed. To confirm visually the damage of railway facilities and deformation of railway tracks in the inspection, it may take a lot of time. It is necessary to carry out the safety inspection more precisely and effectively, for shortening downtime of regular train operation. Therefore to comprehend exactly the characteristics of earthquake ground motions along the target railway, the rapid evaluation of the earthquake ground motions, not only at the points where the seismographs are installed at equal intervals but also at the other points on the railway, are strongly required.<br> &nbsp;&nbsp;In this study, we adopted Miyazaki maglev test line, which has a total length of 7 km, located in the middle coast of Miyazaki prefecture, as a model railway. We tried to estimate the continuous linear S-wave velocity structures and earthquake ground motions along Miyazaki maglev test line. At first, we tried to estimate S-wave velocity structures at two sites where seismographs are installed, using the geophysical exploration such as surface wave exploration and array microtremor survey. Secondly, we estimated the continuous linear S-wave velocity structures on the model railway, based on the S-wave velocity structures estimated by the geophysical exploration method, using the H/V spectral ratios obtained by the high-dense microtremor measurement. Finally, we estimated the high-dense earthquake ground motions along Miyazaki maglev test line by the one-dimensional multiple reflection theory. We confirmed the validity of the continuous linear S-wave velocity structures and the estimated earthquake ground motions along Miyazaki maglev test line, through the comparison with the observed earthquake ground motions.<br>

DOI： 10.3124/segj.67.95

CiNii Books

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：Japanese  

researchmap

Language：English  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1785/0120090052

Web of Science

researchmap

Language：English  

researchmap

Language：English  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Publisher：Architectural Institute of Japan  

The SPatial Auto-Correlation (SPAC) method applied for array records of microtremors provides a S-wave velocity structure by surface wave inversion with sufficient accuracy. The efficiency of the SPAC method has mostly been verified for relatively deep underground structures as a tool of geophysical prospecting. However, efforts to increase its accuracy and develop the tools for measurements and analysis are still necessary for extending and applying the method in practical engineering use, especially for determining shallow velocity structures. We carried out array measurements of microtremors at 7 sites around Kanto area in Japan, where strong-motion stations have already been installed and the underground structures have been determined by other methods, such as PS logging and/or reflection survey. Through the comparison of S-wave velocity structures by various methods, we can conclude that the SPAC method has sufficient precision in practical engineering use.

DOI： 10.3130/aijs.70.17_5

CiNii Books

researchmap

Other Link： http://www.aij.or.jp/paper/detail.html?productId=182331

Language：English   Publisher：Hokkaido University  

CiNii Books

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：Japanese   Publisher：Architectural Institute of Japan  

We proposed a simplified method to evaluate strong ground motions response spectra at ground surface considering the inelastic amplification characteristics of surface layers. We assume that input motions on the engineering bedrock are given by the reviesed Enforcement Order of the Building Standard Law of Japaa This method is far simple and easy to calculate compared to the limit strength method in the revised Building Standard Law of Japan, because this method requires only the 30m depth soil layer data from the surface and substitution from these data to several equations. Despite of simplicity, this method predicts the results of equivalent elastic earthquake response analyses more adequately than the limit strength method in the revised Building Standard Law of Japan.

DOI： 10.3130/aijs.68.73_1

CiNii Books

researchmap

Other Link： http://www.aij.or.jp/paper/detail.html?productId=181257

Application no：特願2013-229418  Date applied：2013.11

Announcement no：特開2015-090287 

researchmap

Application no：特願2013-178187  Date applied：2013.8

Announcement no：特開2015-045616 

Patent/Registration no：特許第6177628号  Date issued：2017.7

researchmap

Application no：特願2013-164646  Date applied：2013.8

Announcement no：特開2015-034715 

researchmap