Pre-Earthquake Geomagnetic Quietude and Event-Day IMF Variability_Dataset

This study tests whether broad-spectrum geomagnetic suppression in the 10 days preceding major earthquakes (M≥5) constitutes a statistically detectable enrichment signal across a seven-year observational window (2010 to 2016). A sample of 350 earthquake event rows (328 unique dates) drawn from seven NOAA National Centers for Environmental Information (NCEI) Significant Earthquake Database exports were compared against 26,250 cross-year control windows derived from hourly OMNI-2 composite solar wind and geomagnetic data spanning 2010 to 2025. Each anchor was normalized to its own calendar-year baseline across 85 retained OMNI metrics. The primary pattern, designated prequiet_ge_30_metrics, required at least 30 of 85 metrics to satisfy two conditions within the D-10 to D-1 window: at least 8 of the 10 pre-event days fell below that metric's anchor-year mean, and the 10-day pre-window average also fell below the anchor-year mean. This condition preceded 32.86% of earthquake rows compared with 25.44% of cross-year control windows (lift = 1.29, p = .003). The enrichment survived Solar Cycle 24-only controls (lift = 1.30, p = .003), same-era 2010 to 2016 controls (lift = 1.28, p = .005), same-year earthquake-screened controls (lift = 1.35, p = .001), unique-date deduplication to 328 dates (lift = 1.27, p = .006), and all seven leave-one-year-out configurations (p range .0003 to .018). Single-day signals, quiet-to-spike transitions, and event-day signatures did not replicate. Pre-window mean ap index was 8.31 for earthquake windows versus 9.04 for controls; pre-window Epsilon, a solar-wind/magnetospheric coupling index derived from upstream solar-wind and interplanetary magnetic-field conditions, was similarly suppressed for earthquake windows relative to controls. A secondary exploratory probe found earthquake windows satisfying the prequiet condition. Elevated IMF Bz polarity reversal activity on the event day was enriched relative to same-year matched controls (lift = 2.15, p < .001). These findings are consistent with sustained broad-spectrum geomagnetic suppression representing a replicable enrichment signal preceding major earthquakes and identify a candidate event-day transition pattern warranting independent confirmation. Keywords: geomagnetic quietude, earthquake precursors, space weather, solar wind coupling, Kp index, ap index, Epsilon coupling function, permutation testing