Study on the Relation between Local Earthquakes and Minute Ground Deformation. Part 2. An Application of the Digital Filtering to the Tiltgram for the Detection of the Minute Anomalous Tilting of the Ground.

Abstract

Digital band-pass and high-pass filters have been applied to the tiltmetric records observed at Wakayama, in order to detect small anomalous ground deformations. Tiltmetric or extensometric observations of the ground deformation are usually disturbed by meteorological and tidal changes and other unknown factors, so the elimination of these disturbances is necessary for the investigation of the minute deformations relating to earthquake occurrences. It is shown that the band-pass filters designed on the basis of the results of the Fourier analysis can be effectively used for this purpose. Small anomalous changes of the ground tilt, which might be related to the local shocks in the Wakayama region, are seen on some of the filtered results, but more observational data are needed to verify the relation between them