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

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Authors

Can Wang, Lilianna E Christman, Simon L Klemperer , Jonathan Glen, Darcy Karakelian McPhee, Bin Chen

Abstract

Anomalous ultra-low frequency electromagnetic (ULFEM) pulses occurring before the M5.4 2007 and M4.0 2010 Alum Rock earthquakes have been claimed to increase in number days to weeks prior to each earthquake. 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 hypocenter, as well as data from a nearby Stanford-USGS site located 42 km from the hypocenter, to analyze 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 greatly on chosen temporal and amplitude detection thresholds. These thresholds are necessarily 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 station. In addition, when comparing specific pulses in the QuakeFinder data and Stanford-USGS data, we find that the majority of pulses do not match temporally, indicating the pulses are not from solar-driven ionospheric/magnetospheric disturbances or from atmospheric lightning, and lack a common origin. Notably, however, our assessment of the temporal distribution of pulse counts throughout the day shows pulse counts increase during peak human activity hours, strongly 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 otherwise standard numerical and statistical test cannot be applied. Yet here we show that exhaustive investigation of many different aspects of ULFEM signals can be used to properly characterize their origin.

DOI

https://doi.org/10.31223/X5CG8P

Subjects

Earth Sciences, Geophysics and Seismology

Keywords

probabilistic forecasting, earthquake precursor, ultra-low frequency, time-series analysis, probabilistic 71 forecasting, magnetic field, Earthquake early warning, ultra-low frequency, magnetic field

Dates

Published: 2021-07-16 01:21

License

CC BY Attribution 4.0 International

Additional Metadata

Data Availability (Reason not available):
QuakeFinder magnetic data are available from Quakefinder and Stellar Solutions Inc.; the Stanford-USGS data are available either from the Stanford or from the USGS

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