Effect on the Subsurface Structure Estimation by the Difference in Responses of Two Horizontal Component Seismographs

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Other Title
  • 水平動地震計特性の違いが地下構造推定に与える影響
  • スイヘイドウ ジシンケイ トクセイ ノ チガイ ガ チカ コウゾウ スイテイ ニ アタエル エイキョウ
Published
2018-11-10
Resource Type
journal article
DOI
  • 10.4294/zisin.2018-1
Publisher
SEISMOLOGICAL SOCIETY OF JAPAN

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<p>Receiver function analysis is an effective method to estimate subsurface structure beneath a seismograph. To apply this method, responses of all three components of a seismograph should be almost the same. However, due to various observation conditions and/or deterioration of the sensors, the response of each component tends to differ. To check the effects of the differences in the sensor response between each component to the receiver function analysis results, we investigated the teleseismograms observed at the N.TSMH station of NIED Hi-net as an example. At this station, the NS component showed a lower response than the other components for frequency ranges lower than 1 Hz. As this feature was resolved after seismograph replacement, we set two analysis periods, before and after the seismograph replacement. Comparing backazimuth dependence of the receiver functions, we first confirmed that the Ps converted phase amplitudes were slightly smaller in specific directions before the replacement than those after replacement. However, there were no clear differences for the arrival times of these phases. Next, we applied the harmonic decomposition analysis to two datasets and estimated the plunge azimuth of the subducting oceanic Moho beneath the station. To evaluate the stability of the estimation results, 1000-time bootstrap tests were conducted for each dataset. Using the dataset before the replacement, the results showed that the oceanic Moho dipped to the west. Based on the dataset after the replacement, the estimated plunge azimuth was in the west-northwest direction. Previous studies show the slab might be inclined to the northwest or west-northwest direction beneath the Bungo channel. This means that the dataset before the replacement was inconsistent with the previous results because of the lower response of the NS component.</p>

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