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北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University >
第69号 >

強震観測におけるSTA/LTA トリガー方式の問題点

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Title: 強震観測におけるSTA/LTA トリガー方式の問題点
Other Titles: Issues in an STA/LTA Trigger Algorithm for Strong Motion Observations
Authors: 吉田, 邦一1 Browse this author
笹谷, 努2 Browse this author
Authors(alt): 吉田, 邦一1
笹谷, 努2
Issue Date: 15-Mar-2006
Publisher: 北海道大学大学院理学研究科地球惑星科学専攻(地球物理学)
Journal Title: 北海道大学地球物理学研究報告
Journal Title(alt): Geophysical bulletin of Hokkaido University
Volume: 69
Start Page: 85
End Page: 95
Abstract: We point out that sometimes a STA/LTA trigger algorithm does not work appropriately for strong-motion observations. The STA/LTA trigger algorithm evaluates the ratio of short-time average(STA) to long-time average(LTA) and is adopted to recognize an earthquake for recording by an event recorder. We observed strong-motion records in the northern part of the Ishikari plain during the 2003 Tokachi-oki earthquake and its largest aftershock. Peak ground accelerations of the records are about 1 m/s^{2 } and peak ground velocities, about 0.3 m/s. However,two of the stations which adopted the STA/LTA trigger algorithm failed in recording during the main shock and the largest aftershock. We evaluate STA/LTA ratios by using the records obtained at other stations in order to investigate factors in not triggering these events. Weak long-period initial motion of P-wave, which was observed during the 2003 Tokachi-oki earthquake and its largest aftershock, make the STA increase slowly. Since the LTA also increases during the slow STA increase, the STA/LTA ratios do not increase enough to trigger an even if peak ground motion is large. We note that the STA/LTA trigger algorithm alone is not perfect for strong-motion observations,especially at an urban site.
Type: bulletin (article)
Appears in Collections:北海道大学地球物理学研究報告 = Geophysical bulletin of Hokkaido University > 第69号

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