Abstract
The strains induced within the grounds are comprised of six components. The strains induced at the ground surface are comprised of four components. The authors have been continuing the observations of the three strain components induced at the ground surface during the earthquakes. In this paper, the observation of the remaining strain component, i.e. vertical normal strain, induced at the ground surface was undertaken using a gauge length of 1 metre. Based on the several earthquake observations, it was found that the vertical strain is similar in magnitude to the principal strain at the ground surface, and also has a tendency to be completely out of phase in time scale with respect to the vertical accerelation.
