The Pulse Azimuth effect as seen in induction coil magnetometers located in California and Peru 2007–2010, and its possible association with earthquakes

Abstract. The QuakeFinder network of magnetometers has recorded geomagnetic field activity in California since 2000. Established as an effort to follow up observations of ULF activity reported from before and after the M = 7.1 Loma Prieta earthquake in 1989 by Stanford University, the QuakeFinder network has over 50 sites, fifteen of which are high-resolution QF1005 and QF1007 systems. Pairs of high-resolution sites have also been installed in Peru and Taiwan. Increases in pulse activity preceding nearby seismic events are followed by decreases in activity afterwards in the three cases that are discussed here. In addition, longer term data is shown, revealing a rich signal structure not previously known in QuakeFinder data, or by many other authors who have reported on pre-seismic ULF phenomena. These pulses occur as separate ensembles, with demonstrable repeatability and uniqueness across a number of properties such as waveform, angle of arrival, amplitude, and duration. Yet they appear to arrive with exponentially distributed inter-arrival times, which indicates a Poisson process rather than a periodic, i.e., stationary process. These pulses were observed using three-axis induction coil magnetometers that are buried 1–2 m under the surface of the Earth. Our sites use a Nyquist frequency of 16 Hertz (25 Hertz for the new QF1007 units), and they record these pulses at amplitudes from 0.1 to 20 nano-Tesla with durations of 0.1 to 12 s. They are predominantly unipolar pulses, which may imply charge migration, and they are stronger in the two horizontal (north-south and east-west) channels than they are in the vertical channels. Pulses have been seen to occur in bursts lasting many hours. The pulses have large amplitudes and study of the three-axis data shows that the amplitude ratios of the pulses taken from pairs of orthogonal coils is stable across the bursts, suggesting a similar source. This paper presents three instances of increases in pulse activity in the 30 days prior to an earthquake, which are each followed by steep declines after the event. The pulses are shown, methods of detecting the pulses and calculating their azimuths is developed and discussed, and then the paper is closed with a brief look at future work.

[1]  Y. Fujinawa,et al.  Emission of electromagnetic radiation preceding the Ito seismic swarm of 1989 , 1990, Nature.

[2]  F. Freund,et al.  Estimating the seismotelluric current required for observable electromagnetic ground signals , 2010 .

[3]  Masashi Hayakawa,et al.  Monitoring of ULF (ultra-low-frequency) Geomagnetic Variations Associated with Earthquakes , 2007, Sensors (Basel, Switzerland).

[4]  V. Grimalsky,et al.  Nonlinear Excitation of ULF Atmosphere–Ionosphere Waves and Magnetic Perturbations Caused by ELF Seismic Acoustic Bursts , 2003 .

[5]  Katsumi Hattori,et al.  Transfer function approach to signal discrimination of ULF geomagnetic data , 2004 .

[6]  F. Freund.  Pre-earthquake signals – Part I: Deviatoric stresses turn rocks into a source of electric currents , 2007 .

[7]  Patrizia Francia,et al.  The 6 April 2009 earthquake at L'Aquila: a preliminary analysis of magnetic field measurements , 2010 .

[8]  A. Fraser-Smith,et al.  An Automatic Real-Time Geomagnetic Activity Monitoring System for the Mad and Adjacent Frequency Bands , 1988 .

[9]  S. Koshevaya,et al.  Investigation of ULF magnetic anomaly during Izu earthquake swarm and Miyakejima volcano eruption at summer 2000, Japan , 2003, 2003 IEEE International Symposium on Electromagnetic Compatibility, 2003. EMC '03..

[10]  K. Gotoh,et al.  Principal component analysis of ULF geomagnetic data for Izu islands earthquakes in July 2000 , 2002 .

[11]  M. Wysession,et al.  An Introduction to Seismology, Earthquakes, and Earth Structure , 2002 .

[12]  S. Picoli,et al.  An improved description of the dielectric breakdown in oxides based on a generalized Weibull distribution , 2006 .

[13]  Y. Tsai,et al.  Geomagnetic fluctuations during the 1999 Chi-Chi earthquake in Taiwan , 2004 .

[14]  O. G. Villard,et al.  ULF magnetic field measurements near the epicenter of the Ms 7.1 Loma Prieta earthquake , 1991 .

[15]  Masashi Hayakawa,et al.  Principal component analysis and singular spectrum analysis of ULF geomagnetic data associated with earthquakes , 2005 .

[16]  C. Dunson,et al.  Investigation of ULF magnetic pulsations, air conductivity changes, and infra red signatures associated with the 30 October Alum Rock M5.4 earthquake , 2009 .

[17]  M. Johnston,et al.  On the reported magnetic precursor of the 1989 Loma Prieta earthquake , 2009 .

[18]  M. Ladd,et al.  Low‐frequency magnetic field measurements near the epicenter of the Ms 7.1 Loma Prieta Earthquake , 1990 .

[19]  Gregory C. Beroza,et al.  Analysis of Ultralow-Frequency Electromagnetic Field Measurements Associated with the 1999 M 7.1 Hector Mine, California, Earthquake Sequence , 2002 .

[20]  The Electromagnetic Observation and Inter Station Transfer Function Analysis before and after the 2002 Dyke Intrusion at Hachijo Island , 2007 .

[21]  Analysis of the ULF electromagnetic emission related to seismic activity, Teoloyucan geomagnetic station, 1998-2001 , 2004 .

[22]  F. Freund.  Pre-earthquake signals – Part II: Flow of battery currents in the crust , 2007 .

[23]  Robert V. Brill,et al.  Applied Statistics and Probability for Engineers , 2004, Technometrics.

[24]  Gary D. Egbert,et al.  Long‐term monitoring of ULF electromagnetic fields at Parkfield, California , 2010 .

[25]  James Cutler,et al.  CalMagNet – an array of search coil magnetometers monitoring ultra low frequency activity in California , 2008 .

[26]  On the reported magnetic precursor of the 1993 Guam earthquake , 2009 .

[27]  V. Zheludev,et al.  Use of wavelet analysis for detection of seismogenic ULF emissions , 2003 .

[28]  John C. Fothergill,et al.  Electrical degradation and breakdown in polymers , 1992 .