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Behavior of the ground during the 1995 Hyogoken-Nambu earthquake is investigated through various analyses on and comparisons with the earthquake records. Behavior of the Holocene clay, a soft clay layer, as well as the fill, the liquefied layer, is shown to affect the response of the ground significantly through effective stress analysis. Earthquake response analysis carried out on the section passing the Sannomiya station indicates that the existence of the Holocene clay and its thickness controls the response of the ground surface to a great degree. It is also shown that there was no deamplification effect caused by the nonlinear behavior of the soil in the area called the damage belt, where damage to houses was especially severe. Incident waves on the top of the upper Osaka Group formation are estimated for several sites where earthquake records were obtained by deconvolution analysis. Their waveforms on the base layer are very similar to each other in a narrow region a few kilometers wide, but are different from those at distant sites, although their PGV are nearly the same at about 80 cm/s. It is shown that the ground shaking observed at the 1995 Hyogoken-Nambu earthquake was characterized mainly by the surface geology, and that it was are controlled by the nonlinear behavior of the soft clay layer and liquefaction of fill.

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The seismic safety of city gas supply has been the major research topic of the writers in past decades. To avoid earthquake hazards due to leakage of gas from breakage of buried pipes, a real-time safety control system, SUPREME, has been deployed and put into practical use. SUPREME employs 3,800 new spectrum intensity sensors and remote control devices to achieve quick gas supply shut off. It monitors the earthquake motion at a large number of sites on a real-time basis, interprets the data, and assesses gas pipe damage in order to decide whether or not the gas supply should be interrupted. The present paper first describes the philosophy behind this system. Second, it describes the performance of the system during the recent Taiwan earthquakes as well as more significant design earthquakes. This system represents the state-of-the-art of computer-operated safety measures, achieved by advanced geotechnical engineering.