Field relations between the spectral composition of ground motion and hydrological effects during the 1999 Chi‐Chi (Taiwan) earthquake

Abstract

The possibility that the frequency content of ground motion in earthquakes affects hydrological responses to earthquakes has yet to be extensively tested in the field. The M w = 7.6 Chi‐Chi earthquake provided an opportunity to do so, as widespread liquefaction and groundwater level changes were recorded by instrumentation in the Choshui Alluvial Fan. Analysis of the resulting data shows that ground motion parameters that measure low‐frequency ground motions are more strongly correlated with coseismic groundwater level change and the occurrence of liquefaction than parameters that measure high‐frequency motions. Notably, horizontal peak ground acceleration, a metric often used to enumerate the strength of ground motion in liquefaction analysis, is weakly correlated with these hydrological effects. It is unclear from this analysis whether low‐frequency ground motion caused coseismic groundwater level change and liquefaction or whether the hydrological changes changed the spectral composition of the observed seismograms during the Chi‐Chi earthquake.