Assessment of a claimed ultra-low frequency electromagnetic (ULFEM) earthquake precursor

Abstract

SUMMARY The rate of occurrence of anomalous ultra-low frequency electromagnetic (ULFEM) pulses has been claimed to have increased days to weeks prior to the M5.4 2007 and M4.0 2010 Alum Rock earthquakes. We re-examine the previously reported ultra-low frequency (ULF: 0.01–10 Hz) magnetic data recorded at a QuakeFinder site located 9 km from the earthquake hypocentre, and compare to data from a nearby Stanford-USGS site located 42 km from the hypocentre, to analyse the characteristics of the pulses and assess their origin. Using pulse definitions and pulse-counting algorithms analogous to those previously reported, we corroborate the increase in pulse counts before the 2007 Alum Rock earthquake at the QuakeFinder station, but we note that the number of pulses depends on chosen temporal and amplitude detection thresholds. These thresholds are arbitrary because we lack a clear physical model or basis for their selection. We do not see the same increase in pulse counts before the 2010 Alum Rock earthquake at the QuakeFinder or Stanford-USGS stations. In addition, the majority of pulses in the QuakeFinder data and Stanford-USGS data do not match temporally, indicating the pulses lack a common origin and are not from lightning or solar-driven ionospheric/magnetospheric disturbances. Our assessment of the temporal distribution of pulse counts shows pulse counts increase during peak human activity hours, suggesting these pulses result from local cultural noise and are not tectonic in origin. The many unknowns about the character and even existence of precursory earthquake pulses means that standard numerical and statistical tests cannot easily be applied. Yet here we show that exhaustive investigation of many different aspects of ULFEM signals can be used to properly characterize their origin.

Research Progress on Magneto-Refractive Magnetic Field Fiber Sensors

“…Magnetic field sensors (namely magnetometers) are an important tool for obtaining magnetic information, with plenty of applications in geophysics, biomedicine, industrial production, and other fields [ 1 , 2 ]. For instance, researchers employ magnetic field sensors to capture low-frequency weak magnetic signals before earthquakes so that pre-warning can be realized [ 3 ]. Combined with Magnetic Resonance Imaging (MRI) technology, magnetic field sensors can assist medical staff in disease diagnosis [ 4 ].…”

Case‐Control Study on a Decade of Ground‐Based Magnetometers in California Reveals Modest Signal 24–72 hr Prior to Earthquakes

“…Wang et al. (2021) note that no statistical study combining signals from pairs of nearby sites has been done in the past. We used a case‐control design attempting to distinguish, for each site‐pair and earthquake, the period immediately before an earthquake (a “case,” which we also call a precursor or p‐period) from other prior periods (“controls,” which we also call quiescents or q ‐periods). This case‐control design allowed many of the differences in overall measurements at each site to be handled naturally.…”

“…Wang et al. (2021) note that no statistical study combining signals from pairs of nearby sites has been done in the past.…”

“…Moreover, anecdotal precursor signals must be carefully vetted to ensure that they are not actually due to unrelated sources (e.g., incidental human activity), such as described in Wang et al. (2021). In a statistical study, such as this one, multiple earthquake observations are required to demonstrate a consistent relationship between the observed phenomena and earthquakes.…”

“…The unmatched density of the QuakeFinder magnetometer array makes this cross-spectral analysis (Nichols et al, 1988) possible. Wang et al (2021) note that no statistical study combining signals from pairs of nearby sites has been done in the past. 3.…”