Abstract
The effect of rainfalls appeared on the records of tiltmeters and strainmeters at Yura were investigated in relation to the amount of rainfalls. It was found that (1) the peak values in the tilt and strain due to rainfall (per 1 mm of rainfall) showed remarkable temporal changes and the conversion of the trend corresponded fairly to that in the secular tilt and strain observed by the same instruments, (2) the effect of rainfall in the summertime, namely in the wet season was smaller than that in the wintertime, namely in the dry season, and (3) an annual variation appeared on a strain component could be explained as the effect of rainfalls. Especially the good correspondence between the rainfall effect and the secular change means that the tilt and strain response of the ground to rainfall might change according to the crustal stress, probably by the change of the permeability of the underground water.
