We propose an improved fault model of the Hyogo-ken Nanbu Earthquake for which an asperity is placed on the branch fault (branch fault model). The branch fault model is based on the result of source inversion which suggests that the rupture of the fault propagated also to the branch fault on the way. The result of the ground motion simulation by using the branch fault model agree better with observed motions than the results by using the previous fault model, for the sites located east of the fault for which the branch fault contributes much.

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The seismic resistance of buried pipeline was conventionally evaluated only by the strength of material used for the pipeline. Consequently, the buried pipeline with weak-strength material was recognized as the pipe to be replaced or to be reinforced. Therefore, the conventional method could be over-investment if it is used for the determination of replacement / reinforcement plan.
Here, it is obviously important to develop the new seismic resistance evaluation method for buried pipes where both the soil conditions and the network shapes are taken into consideration, in order to make the replacement / reinforcement plan to be effective.
In this new method, the seismic resistance of the buried pipes can be evaluated reasonably through comparison between the strength of the buried pipes and the external forces on the pipes induced by design earthquake motion.

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During the 2004 Mid Niigata Earthquake, there was large difference between the earthquake motion amplitudes at the K-NET station and the JMA station in Ojiya, Niigata prefecture. The damage to low-rise buildings around the sites was relatively little for such large strong motions. To find the cause of the amplitude difference and the damage level, we conduct earthquake response analyses of surface soil layers considering soil nonlinearity and then earthquake response analyses of building models. These analyses show that the difference of strong motions at the two sites mainly depends on the surface soil amplification within approximately 3 meters below the surface. And by earthquake response analyses of building models, we confirm that the analytical results account for the little damage to low-rise buildings in the earthquake.

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