Strong Ground Motions and Damage Investigation of Buildings in the Vicinity of the Surface Faulting of the 2016 Kumamoto Earthquake in Japan

Abstract eng:
This paper reports characteristics of the strong ground motion records and the results for investigating building damage near the surface faulting of the 2016 Kumamoto earthquake. The EW components of the strong motions in Mashiki City and Nishihara Village were dominant at periods longer than 1-2 sec, and showed clearly the fling steps; they were caused by the motion of the hanging wall of the normal/right-lateral faulting, and were dominant in the direction of the faulting slip. The forward directivity pulses, on the contrary, which were dominant in the direction normal to the fault plane (close to the NS components), were not very clear in the records. This is probably due to the complex faulting process and/or the propagation effects of the seismic waves in the local complex media. On the other hand, the records of the EW components in the Mashiki City showed the large amplitudes at about 1 sec; they were probably the forward directivity pulses. The results of the building investigation indicated that most of severe damage occurred in those directly above the surface faulting, because of its slip deformation. And, almost all severe damaged buildings were very old wooden houses/apartments, whereas new wooden or RC buildings showed very minor damage. In the Shimojin area, particularly, the ground motion was probably not strong enough to cause severe damage, and thus, the highest damage was Grade 3. All of them were very old wooden buildings and directly above the surface faulting. Even though the best counter measure for buildings near active faults is to avoid them, it is unrealistic to prohibit buildings in such areas shown in this study, because the exact locations of the surface faulting are very difficult to identify. In fact, they differed from those of the actual surface faulting, because of the young alluvial/volcanic sediments and the artificial land development. In addition, the recurrence intervals of the active faults are extremely long (usually several thousand years), as compared with the lifetime of a building. And the most importantly, various safety counter measures are effective, even for the building directly above the surface faulting. For example, the new wooden houses with the mat foundation of RC could prevent the slip deformation from reaching the building, and the combinations of the shear wall and light roofs prevented severe damage. On the other hand, the old Japanese traditional houses generally suffered severe damage, but their structural flexibilities could prevent collapsing by following the slip deformation. The collapsed buildings were generally very old and lacked both the sufficient earthquake-resisting structural members and the effective connections among them. .

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