Ground Tilts Derived from Seismometers: Examples from Taiwan
Abstract
Seismometers not only record translational motions from earthquakes, but also rotational motions induced by surface deformations from environmental processes. The rotational motions can be generated by shear strains from ground tilts. At several broadband seismic stations near rivers in Taiwan, we found that ultra long period seismic signals (ULP) induced by ground tilts were generated by loading from fluvial processes due to precipitation during typhoon and heavy rainfall events. The tilt signals help to monitor local load changes due to environmental processes. Those signals show much higher amplitudes on the horizontal components than those on the vertical component in seismograms because the ground tilt causes the gravitational acceleration to be partitioned into the horizontal components. Thus, we want to test if the tilt signals can also be found in continuous recordings from strong-motion accelerometers near rivers. Here, we analyze the rain-related tilt signals from the broadband seismometer, the strong-motion seismometer, and the tiltmeter at the station Ninganchiao (NACB) of Taiwan to better understand characteristics of tilt signals observed by the three different sensors and how the seismometers respond to surface tilt. For the ULP tilt signals, the broadband seismometer gives robust and consistent results with the tiltmeter. The estimated tilts from the broadband seismometer with frequencies below the angular frequency of lower corner frequency of instrument response are consistent with the recordings from the tiltmeter. However, the tilts from the strong-motion seismometer have higher tilt values than those from the broadband seismometer and the tiltmeter. We plan to test the hypothesis that the long period signals in strong motion sensors may also include translational motions and DC offsets generated by slight changes of the sensor's mass.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S51D0371Y
- Keywords:
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- 9805 Instruments useful in three or more fields;
- GENERAL OR MISCELLANEOUSDE: 9820 Techniques applicable in three or more fields;
- GENERAL OR MISCELLANEOUSDE: 1895 Instruments and techniques: monitoring;
- HYDROLOGYDE: 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS