Evaluation of Ground Motion for Urban Structures by Near Field Earthquake

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To mitigate urban earthquake disaster, we have to take in account effects of near-field ground motion in earthquake resistant design of urban facilities as well as in urban planning. Such process may include specification of design earthquake motion and/or seismic loading, and development of seismic micro-zoning maps. The research topic of our group aims to facilitate the process from engineering points of view. The topic of this group was sub-divided into the following three sub-topics. Each sub-topic was originally assigned to 12 researchers consisting of our group, but most researchers have involved in not only one sub-topic but also two or three.1. Input Ground Motion and Seismic Loading.Near-field ground motion and its effects on earth pressure, liquefaction potential and ground displacement have been studied to obtain general guidelines specifically used for structural design of urban facilities such as buildings, bridges, tunnels, and buried pipelines.2. Worst Near-field Motion and Its EffectsIn structural design and disaster management, we have to pay attention to special cases where standard design motion and loading are exceeded in somehow or other. Studies under this sub-topic have included causes and effects of worst cases such as the so-called seismic disaster belt and near-field effects on important structures like dams.3. Seismic Micro-zonationSince ground motion intensity varies due to local site effects, we should bear in mind the variety in urban planning and design of lifeline systems. The distribution of higher seismic intensity in the case of the 1995 Hyogoken-nanbu earthquake has been evaluated taking into account source and path effects as well as topographical and geological irregularities, and an effective procedure has been developed to detect the local site effects by means of microtremor measurement.