Fig. 6From: Design and operation of a 1500-m laser strainmeter installed at an underground site in Kamioka, JapanSeismic waves associated with the Fukushima earthquake (Mw 6.9) that occurred at 20:59:49 (UTC) on November 21, 2016 (expansion positive); the inset is a magnified view around the initial motion. The peak-to-peak strain amplitude was 6.4 × 10−7. The fringe signals were normally converted to strain without saturation or discontinuity due to cycle slipBack to article page