Fig. 5
Background strain spectrum for the 1500-m laser strainmeter (red) compared to those for other strainmeters: Piñon Flat Observatory (PFO, black, Berger and Lovberg 1970; Berger and Levine 1974), Baksan (pink, Buklerskii et al. 1995), Gran Sasso (gray, Crescentini and Renzella 1991), Inuyama (green, Araya et al. 2001), and Black Forest Observatory (BFO, orange, Zürn et al. 2015), including the 100-m laser strainmeter at Kamioka (blue, Araya et al. 2007). Detectable strain levels in amplitude are shown as dash-dotted lines. The detection limit for the 1500-m strainmeter is estimated as better than 10−12 in the 2–20 mHz range and 10−11 in the 1 mHz–10 Hz range