Fig. 9From: Cross-validation of independent ultra-low-frequency magnetic recording systems for active fault studiesa Same time series as Fig. 8b but with a 200-s high-pass filter, and with the addition of the FRN fluxgate-magnetometer time series. b Expanded view of gray box in a, ~ 20 min of data, showing what we interpret as a Pi2 irregular geomagnetic pulsation spanning ~ 3 minBack to article page