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 Niigataken Chuetsuoki Earthquake in 2007 recorded by VSE355G2
at Kashiwazaki (KZK) observation site (Fig. 1) of F-net.
The reason will be that the ground acceleration level of the Niigataken Chuetsu-oki Earthquake in 2007
at the observation point exceeded observable limit of the VSE 355G2.
[Fig.2 Observable region of VSE355G2 and maximum acceleration values of Teradomari (NIG016), K-NET]
We will replace VSE355G and VSE355G2 seismometers with VSE355G3 seismometers which has wider observable region.
[Fig.1 Velocity waveforms at Kashiwazaki(KZK), 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 200gal at 5Hz.
Fig.3 is 1Hz low pass filtered velocity seismograms which is indegrated from accelerograms at Teradomari (NIG016),
K-NET, which is 44km north east of Kashiwazaki (KZK), F-net.
Maximum amplitude values of EW components are 16.3cm/s(358gal), respectively,
which are indicated by red solid circles in Fig.2.
These acceleration values exceeded VSE's limit.
[Fig.3 0.1Hz low pass filtered velocity waveforms at Teradomari (44km north east of Kashiwazaki), K-NET]