Comment on "systematic analysis of shear-wave splitting in the aftershock zone of the 1999 Chi-Chi, Taiwan, earthquake : shallow crustal anisotropy and lack of precursory changes, by Yungfeng Liu, Ta-Liang Teng, and Yehuda Ben-Zion

Liu et al. (2004) systematically analyze the parameters of shear-wave splitting before and after the 1999 Chi-Chi earthquake in Taiwan. They claim that they see no evidence for the temporal changes in shear-wave time delays, which some of us use to monitor the buildup of stress before earthquakes. In fact, the only diagram where one would expect to see the type of temporal changes observed elsewhere, figure 14a in Liu et al. (2004), does show two types of temporal variations of time delays. Here, we fit least-squares lines to these temporal changes and show that the duration/earthquake-magnitude relationships of these various changes agree very well with those seen elsewhere. Thus, the behavior before the Chi-Chi earthquake lends further support to the use of shear-wave splitting to stress-forecast the times and magnitudes of impending earthquakes.