We have used VSE type seismometers for strong velocity waveform observation,
which cannot be covered by STS seismometer.
But we obtained distorted waveforms of the 2003 Tokachi-oki earthquake recorded by
VSE355G2 at Kamikineusu (KMU) observation point (Fig. 1) of F-net.
The reason will be that the ground acceleration level of the 2003 Tokachi-oki earthquake at the
observation point exceeded observable limit of the VSE 355G2.
[Fig.2 Observable region og VSE355G2 and maximum acceleration values of Samani(HKD110), K-NET]
We will replace VSE355G and VSE355G2 seismometers with VSE355G3 seismometers which has wider observable region.
[Fig.1 Velocity waveforms at Kamikineusu(KMU), F-net, recorded by VSE355G2]
Fig.2 indicates observable region of VSE355G2 defined by frequency and acceleration.
The observable region lies between two blue lines. The observable region of VSE355G
seismometer is same as that of VSE355G2.
The VSE355G2 seismometer can observe seismic wave less than 100gal at 1Hz.
Fig.3 is 1Hz low pass filtered acceleration seismograms at Samani (HKD110), K-NET,
which is 12km south of Kamikineusu (KMU), F-net. Maximum amplitude values of EW and NS
components are 100gal and 111gal, respectively, which are indicated by red solid circles in
Fig.2. These acceleration values exceeded VSE's limit.
[Fig.3 1Hz low pass filtered acceleration waveforms at Samani (12km south of Kamikineusu), K-NET]