Journal of Japan Association for Earthquake Engineering Vol. 17(2017) No. 4

This paper describes the dynamic characteristics of existing buildings (one is a reinforced concrete structure, and the other is a steel) in Miyagi Pref., Japan. In this paper, the authors used the long-term ambient vibration data and earthquake responses data, which were recorded by a monitoring system with high-performance seismic sensors installed by IRIDeS, Tohoku University, to examine response characteristics of the buildings. As a result of the analysis of the vibration records, it is found that the natural frequency of the RC structure shows stronger correlation with temperature than the S structure. The influence of the temperature dependency is included in the amplitude dependency of the 1^st natural frequency. Amplitude dependency become clear by removing temperature dependency.

For an understanding of the ground-motion characteristics of deep-focus earthquakes around the Ogasawara Islands, in this study, we first investigated the spatial distributions of strong motion indexes for past events and their attenuation relationships, and estimated the non-geometric attenuation parameters for each deep-focus event. We found that the observed attenuation relationship differs among each region in Japan: the intrinsic and/or scattering attenuation is weak in order of the paths to the fore-arc of East Japan, the back-arc of East Japan, and West Japan and the region from the Izu Peninsula to the Izu-Ogasawara Islands. The complex distribution of ground motions is expected to be caused by the presence of the subducting Pacific Plate and the heterogeneous attenuation structure of upper mantle in East Japan. In addition, we found that the difference between short-period non-geometric attenuation characteristics along the path to the fore- and back-arcs of East Japan may depend on the event location probably because of the three-dimensional curved shape of the Pacific Plate. Considering the observed regional variation of attenuation relationship, we proposed an empirical equation of gourd-motion attenuation relationship for deep-focus earthquakes. We also estimated correction terms for the amplification by deep sediments and shallow soft soils for deep-focus earthquakes. Using the empirical equation of ground-motion attenuation relationship and the correction terms, we carried out the ground motion predictions for past deep-focus earthquakes and compared the results with the observations.

Large vertical acceleration of 3866 gal was recorded on the ground surface at KiK-net West-Ichinoseki (IWTH25) station during the 2008 Iwate-Miyagi Nairiku earthquake. This large UD component is strongly asymmetric with respect to the horizontal zero-axis, whereas NS and EW component are broadly symmetric. It has been found that this asymmetric waveform is able to be predicted by the elasto-plastic dynamic response analysis inputting both horizontal and vertical input wave simultaneously. Also, large acceleration was observed during the 2011 Off the Pacific Coast of Tohoku Earthquake at K-NET Tsukidate (MYG004) station. Many researchers claim that this large acceleration was caused due to the partial uplifting of the foundation of seismometer. In this paper, we showed that the dilatancy or volume change of soil can be one of the possible reasons for that large acceleration.

During and after big earthquakes power outage often occurs, thus it is difficult to keep continuing energy supply. In this study by using energy regeneration, an active seismic isolation device having a charging function is proposed. First, rotational velocity - electromotive force characteristics of motors during actuation and regeneration is modeled based on the experimental data. Second, artificial long-period ground motions for design are created by using acceleration data of ground motions. Then, design variables of the seismic isolation device which focus is on the charging function are optimized using a genetic algorithm. By numerical simulation, it is confirmed that the proposed energy-regeneration active seismic isolation device shows response reduction and regeneration effect as required against both long-period and short-period ground motions.

The Kumamoto Earthquake of April 16, 2016 was associated with widespread liquefaction-induced damage in the Kumamoto Prefecture of Japan. Our investigation revealed that the earthquake induced liquefaction at a significant number of locations in a 80-km long zone extending along the earthquake source faults. This paper presents distribution of the liquefied sites and their effects on buildings and infrastructures during the earthquake. Additionally, the distance from the epicenter to the farthest liquefied site is compared with previous Japanese earthquakes, and intensities of ground motion that caused liquefaction are discussed. Finally, land conditions where severe and widespread liquefaction occurred are investigated.

We investigated tombstone fall-down rates and damages rates of wooden houses from April 27 to 29 in 2016 to estimate the distribution of the ground motion intensity around the near source region of the 2016 Kumamoto Earthquake (MJ7.3), Japan. We investigated 2 regions; Mashiki-machi Miyazono where observed JMA seismic intensity 7 and region where surface earthquake faults appeared. According to the result of tombstone fall-down rates, there is not so different in 2 regions. Almost 100% tombstones fell down in some grave sites. But damages rates of wooden houses differ from each other. In Mashiki-machi Miyazono 61% wooden houses were collapsed. In the region where surface earthquake faults appeared damages rates of wooden houses were 0-33%.

In order to clarify the factors of strong ground motions at the KiK-net Mashiki station which generated a large acceleration of more than 1G caused by the largest foreshock (Mj6.5) of the 2016 Kumamoto earthquake, we performed ground identification analysis and one-dimensional wave propagation analysis using the vertical array observation records and analyzed the strong motions in detail. In addition, we estimated the bedrock (S wave velocity 2700m/s) ground motions of the largest foreshock and evaluated their acceleration levels. As a result, the ground motions have a significantly larger amplification at higher frequencies than about 2 - 3Hz. And the effect of large site amplification of the ground shallower than the seismic bedrock of approximately depth of 250m has been shown as one of the factors of strong ground motions. On the other hand, seeing that a short-period spectral level of earthquake has an average value of inland crustal earthquake, and the estimated bedrock spectra can be mostly described from the theoretical bedrock spectra at the seismic bedrock considering the seismic source and propagation characteristics based on the omega-square model of earthquake, we showed the largest foreshock is not an abnormal earthquake from the viewpoint of earthquake magnitude and ground motion level. However, because the bedrock spectra has a slightly higher value than the theoretical bedrock spectra at approximately 0.4 - 4Hz, near-fault rupture directivity effect due to the fault rupture propagation has been shown in the strong ground motions at the KiK-net Mashiki station. It has been found that the large acceleration amplitude in the ground surface of the KiK-net Mashiki station by the largest foreshock was caused by large site amplification of shallow ground and near-fault rupture directivity effect.

2011 Great East Japan Earthquake resulted in tremendous victims due to tsunami. Influenced by psychological bias, most people did not start evacuation directly after detecting earthquake. Many people were triggered by others going and passively began to set out. It caused delay of evacuation. Furthermore some were struck by tsunami despite reaching evacuation space because tsunami attacked at several evacuation spaces which had been regarded as safety. Considering the teachings for disaster mitigation, it is important to instigate experimental study about preferable ICT which dramatically progresses these days. This paper aims to analyze the past tsunami evacuation and propose new proof of ICT, using multi-agent model. Human behaviors such as following are modeled. Simulation of Great East Japan Earthquake and case studies as countermeasures are carried out. Finally this paper propose that some people have ICT terminals which project safety pass onto surroundings and emerge human flow with collecting the projections and its followers neighborhood. This should be an effective scheme which coordinates feature of human and ICT.

The eighth meeting of the Microtremor Research Camp (MRC) was held in Ohno City, Fukui Prefecture from September 30th to October 2nd in 2016, and MRC carried out microtremor measurement in Katsuyama Basin that is constituted with deposits of Kuzuryu River. This measurement consists of 19 sites of micro-array measurement (MRM) and 67 sites of single-point measurement (SPM). This paper reports the outline of this measurement and eventually presents the distribution of predominant frequencies (DPF) in the basin obtained through the analysis of horizontal-to-vertical ratio (HVR) at SPM sites. As the result, the large differences of DPF and PSV (peak spectral values) in between Quaternary terrace deposits and alluvial deposits are clarified.

Serious damage with tilting of housings for pumping facilities in clean water distribution field, which are located near the epicenters of the 2016 Kumamoto earthquake sequence, was occurred due to the strong motions. In this study, aftershock observations were conducted at the damage sites in order to evaluate the site effects. Seismic waveforms at the sites during the earthquakes were then estimated based on the site effects and the characterized source model. The estimated ground motions will be useful in the detailed study of the damage mechanism.

Janes' Residence in Chuo Ward, Kumamoto City, Japan which is a prefectural important cultural property was collapsed due to the foreshock and the main shock of the 2016 Kumamoto earthquake. In this study, to evaluate ground motions at the collapse site, temporary aftershock observation was conducted at the site and Suizenji Governor Station site. The result indicates that the ground motions at the collapse site were similar to those at the station site. At Suizenji Governor Station, where waveforms during the foreshock and the main shock were not released, the waveforms were estimated based on the substitution method for site amplification factor.