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Earth, Planets and Space
Fig. 12 | Earth, Planets and Space

Fig. 12

From: Cross-validation of independent ultra-low-frequency magnetic recording systems for active fault studies

Fig. 12

a Data for the period 15:18–15:30 UTC, April 17, 2017. b–g Cross-correlation coefficients calculated at 20-s intervals over the same time period between all pairs of north-oriented sensors. b Zonge ANT4 versus EMI BF4, c Zonge ANT4 versus QFido3, d EMI BF4 versus QFido3, e Zonge ANT4 versus Fresno Fluxgate, f QFido3 versus Fresno Fluxgate, g EMI BF4 versus Fresno Fluxgate. In each panel, the horizontal blue line shows and is labeled with the mean of the cross-correlation coefficients for the 12-min period, and the red dashed line shows an empirically estimated threshold of 0.5. Cross-correlations of USGS-Stanford and QuakeFinder records b–d are carried out with 200-s high-pass filtered data streams as used elsewhere in this paper; cross-correlations with the Fresno Fluxgate magnetometer that only records at 1 Hz sample rate e–g use a data stream bandpass-filtered with a 1–200-s Butterworth filter

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