| dc.description.abstract | Seismic microzonation for Taipei Basin has been included in the latest version of Seismic Design Code for Buildings, Taiwan. It is divided into four zones according to a corner period, and zone 1 has the longest corner period of 1.60 seconds. However, the deepest soil in Taipei Basin is as deep as 700 meters, the natural period may be more than 3 seconds. This study attempts to analyze the strong-motion records in Taipei Basin from major earthquakes which impact Taipei in the past twenty years. I found that at least for an earthquake which was occurred offshore Hualien on March 31, 2002, and at Luzhou and Wugu area, the corner period is more than 3 seconds.
This study classified the selected earthquakes into three types: subduction zone interface earthquake, subduction zone intraslab earthquake, and crustal earthquake. I calculate an average normalized response spectrum for each strong-motion station, then estimate the corner period and amplification factor from the average normalized response spectrum. Microzonation map for Taipei Basin is drawn based on the distribution of corner periods.
The result shows that the corner period for subduction zone interface earthquake is longer than that of the other two types, and there is positive correlation between corner periods and the natural period of a site. The 331 Hualien earthquake, which has caused hazard in Taipei Basin, has corner period longer than 3 seconds, but not all the subduction zone interface earthquake has a corner period as long as 331 Hualien earthquake. If we use the average normalized response spectrum to estimate a corner period, the longest corner period is only about 2.2 seconds. In this study, the corner periods from the average normalized response spectrum was used to construct a microzonation map for Taipei Basin. The result indicates that microzonation map from subduction zone interface earthquake is similar in pattern with that in the Seismic Design Code for Buildings. It can be seen that the microzonation is mainly controlled by subduction zone interface earthquakes. It can re-analyzed in the future with more earthquake data to obtain more reliable results and to update the Seismic Design Code for Buildings so that hazard may be mitigated.
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