a preliminary report of two earthquakes recorded by both broadband and rotation sensors c. c. liu 1,...
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![Page 1: A Preliminary Report of Two Earthquakes Recorded by both Broadband and Rotation Sensors C. C. Liu 1, B. S. Huang 1, and W. H. K. Lee 2 1 Institute of Earth](https://reader036.vdocuments.us/reader036/viewer/2022062721/56649f1f5503460f94c37b9b/html5/thumbnails/1.jpg)
A Preliminary Report of Two EarthquakesRecorded by both Broadband and Rotation Sensors
C. C. Liu1 , B. S. Huang1, and W. H. K. Lee2
1 Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan2 U.S. Geological Survey, Menlo Park, CA 94025, USA
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Figure 1.
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Figure 2.
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Figure 3.
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Figure 4.
Re-plotting the observed data for the September 26, 2005 earthquake on the same y-axis scale for the broadband velocity signals (top two frames) and for the rotation velocity signals (bottom 3 frames).
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Figure 5.
Integrated broadband and rotation signals for the September 26, 2005 earthquake.
Same y-axis scale for the broadband velocity signals (top two frames) and for the rotation velocity signals (bottom 3 frames).
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Figure 6.
Power spectra for the recorded signals of the September 26, 2005 earthquake.
Y-axis scale is different for each of the broadband velocity signals (top two frames) and for each of the rotation velocity signals (bottom 3 frames).
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Figure 7.
Power spectra for the displacement signals of the September 26, 2005 earthquake.
Y-axis scale is different for each of the broadband displacement signals (top two frames) and for each of the angular rotation signals (bottom 3 frames).
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Figure 8.
Re-plotting the observed data for the January 8, 2006 earthquake on the same y-axis scale for the broadband velocity signals (top two frames) and for the rotation velocity signals (bottom 3 frames).
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Figure 9.
Integrated broadband and rotation signals for the January 8, 2006 earthquake on the same y-axis scale for the broadband velocity signals (top two frames) and for the rotation velocity signals (bottom 3 frames).
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Figure 10.
Power spectra for the recorded signals of the January 8, 2006 earthquake.
Y-axis scale is different for each of the broadband velocity signals (top two frames) and for each of the rotation velocity signals (bottom 3 frames).
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Figure 11.
Power spectra for the displacement signals of the January 8, 2006 earthquake.
Y-axis scale is different for each of the broadband displacement signals (top two frames) and for each of the angular rotation signals (bottom 3 frames).
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Figure 12.
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Conclusion
• Since 1 μrad in-plane tilt will introduce about 1 μg on a horizontal accelerometer with active axis in that same plane, our observation indicates that the effect of angular rotation for an earthquake with moment magnitude of about 5 cannot be ignored in the double integration of the translational acceleration to obtain displacement.
• Our preliminary observations from two earthquakes suggest that angular rotation is important event in the mid-field of an earthquake. This has important consequences in analyzing near-field strong-motion data recorded traditionally for translation motion only.
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Conclusion (cont.)• Much work remains to be performed on our observed data.
One important item that we have not done is calibrating the rotational transducer in the field.
• At station HGSD, the deployment is not optimal: the broadband seismometer is located 100 m deep in a borehole, while the rotational transducer is at the surface.
• At the same site (within 50 m or less), there is a downhole strainmeter that also recorded these two earthquakes, as well as a continuous GPS station.
• We lacked a traditional accelerometer at the site, although several free-field accelerographs (operated by the Central Weather Bureau) are nearby.
• We also need to examine the earthquake source parameters carefully.
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Conclusion (cont.)• We are aware that several authors had published papers on
their recorded rotation motions. However, we have not yet compared our results with theirs carefully.
• Although a more detailed study of the observed data is underway, we release this draft to the Workshop participants for discussions. We solicit comments and suggestions. We have another R-1 transducer to be deployed soon, and will welcome suggestions for designing a better deployment.
• Please contact Willie Lee at <[email protected]>.