SUMMARYThe 11 March 2011 M 9.0 Great East Japan earthquake generated significant long-duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of a tall building at 770 km from the epicenter of the mainshock and other related or unrelated events show how structures sensitive to long-period motions can be affected by distant sources. Even when the largest peak input motions to the building is about 3% g, the strong-shaking duration was about 140 s. The 300-to 1000-s prolonged responses of the building are primarily due to a combination of site resonance (e.g. structural fundamental frequency~0.15 Hz and site frequency~0.13-0.17 Hz) and low damping (~1-2%) of the structure. Response modification technologies can improve the response of the building during future earthquakes. The need-to-consider risks to such built environments from distant sources are emphasized.

We develop empirical regression relations for estimating waveforms of horizontal and vertical ground motions in a period range of 0.1 to10 seconds caused by subduction-zone and crustal earthquakes using many strong motion records all in Japan. The relations are provided for 5 % and 1 % damped acceleration response spectra, energy spectrum, average of group delay time, and standard deviation of group delay time. The waveforms with site-specific amplification and phase spectra are easily calculated by the empirical relations using the outer-fault parameters, rupture starting points, delay time among rupture starting points, and the location of the strong motion stations in interest. We show that waveforms calculated by the empirical relations for the hypothetical Nankai earthquake are consistent with waveforms calculated by the theoretical method using three dimensional structure model and inner-fault parameters as well as outer-fault parameters in previous studies.

During the 2011 Tohoku-oki earthquake, a large number of response records from various types of buildings were obtained. The records give us the actual motions of buildings during the exceptionally large earthquakes that are considered comparable with design earthquakes. Various types of earthquake response records have been collected, and their properties with several buildings that will exhibit implications for structural design are discussed.

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A sparsely instrumented 55-story building in Osaka, Japan, had recorded unprecedented, severe, and long-duration, long-period resonating responses during the 11 March 2011 M9.0 Tohoku earthquake that occurred at 767 km distance. Thereafter, studies of the records resulted in the implementation of a significant retrofit design, comprising dampers and buckling restrained braces (BRBs). The responses of the retrofitted building were also recorded during the 24 April 2016 M7.3 Kumamoto earthquake that occurred at 478 km. The earthquake and on-demand acquired ambient response data are analyzed in this study to assess the impact of this rare, retrofitted and instrumented tall building subjected to long period strong shaking from events originating at far distances. As expected, the fundamental frequency and critical damping ratio of the building increased, albeit small, after the retrofit as compared to before the retrofit. Increase of damping percentage is a positive finding and indicates that even larger percentages may be attained under shaking stronger than the 2016 event. The records indicate that the building still experiences significant resonance, torsion, as well as a beating effect.