Japan Meteorological Agency (http://www.jma.go.jp/) is operating the nationwide seismic intensity network that has more than 600 stations. The instrument, which calculates the instrumental seismic intensity, is called JMA 95 type seismic intensity meter. Acceleration records of the seismic intensity meters at all stations are distributed from the Japan Meteorological Business Support Center (http://www.jmbsc.or.jp/) at cost. There are two types of file format, i.e. the ASCII format and the binary format.

The ASCII format data at one station for an earthquake consists of three files with extensions ".ans", ".aew" and ".aud", corresponding to three components. ViewWave tris to read all components by specifying one of those files. A binary data file contains three-component accelerograms for a minute. When one file is selected, ViewWave reads it and looks for the next file.