Review: Progress in Rotational Ground-Motion Observations from Explosions and Local Earthquakes in Taiwan

Abstract

Rotational motions generated by large earthquakes in the far field have been successfully measured, and observations agree well with the classical elasticity theory. However, recent rotational measurements in the near field of earthquakes in Japan and in Taiwan indicate that rotational ground motions are 10 to 100 times larger than expected from the classical elasticity theory. The near-field strong-motion records of the 1999 M w 7:6 Chi-Chi, Taiwan, earthquake suggest that the ground motions along the 100 km rupture are complex. Some rather arbitrary baseline corrections are necessary in order to obtain reasonable displacement values from double integration of the acceleration data. Because rotational motions can contaminate acceleration observations due to the induced perturbation of the Earth's gravitational field, we started a modest program to observe rotational ground motions in Taiwan. Three papers have reported the rotational observations in Taiwan: (1) at the HGSD station (Liu et al., 2009), (2) at the N3 site from two TAiwan Integrated GEodynamics Research (TAIGER) explosions (Lin et al., 2009), and (3) at the Taiwan campus of the National Chung-Cheng University (NCCU) (Wu et al., 2009). In addition, Langston et al. (2009) reported the results of analyzing the TAIGER explosion data. As noted by several authors before, we found a linear relationship between peak rotational rate (PRR in mrad=sec) and peak ground acceleration (PGA in m=sec 2) from local earthquakes in Taiwan, PRR 0:002 1:301 PGA, with a correlation coefficient of 0.988.

Observing Rotational and Translational Ground Motions at the HGSD Station in Taiwan from 2007 to 2008

“…However, our data set is small and we will need far more data to establish any significant relationship. Nevertheless, Lee et al (2009) performed a data fitting to these data and to the data presented by Takeo (2009), and they discussed this linear relationship.…”

Analysis of rotation sensor data from the SINAPS@ Kefalonia (Greece) post-seismic experiment—link to surface geology and wavefield characteristics

“…Lee et al (2009b) already showed the difference in the slope between the Takeo (2009) and Liu et al (2009) datasets. We suggest that this can be explained by an effect of the magnitude on the rotations.…”

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

“…Despite the above reservations, installed R-1 rotational seismometers have for instance recorded several hundred local earthquakes and two explosions in Taiwan [74]. The largest peak rotational rate recorded at the HGSD station (up to early 2008) was from an earthquake with magnitude 5.1 at 13:40 UTC 23 July 2007.…”