Local Geomagnetic Events Associated with Displacements on the San Andreas Fault

Breiner, Sheldon; Kovach, Robert L.

doi:10.1126/science.158.3797.116

Cited by 16 publications

(4 citation statements)

References 5 publications

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“…In fact, magnetic phenomena associated to earthquakes and volcanic eruptions have been widely studied in Japan [13] and the U.S. utilizing highly sensitive instruments [14]. Some noteworthy results in the Ultra Low Frequency (ULF) band regarding very strong seismic events include the Alaska earthquake in 1964 [15] and other earthquakes which occurred near magnetic network observatories [16]. However, different interpretations for the observed ULF anomalies though a controversy erupted over their connection to the seismic events [17,18].…”

Section: Introductionmentioning

confidence: 99%

The Central Italy Electromagnetic Network and the 2009 L'Aquila Earthquake: Observed Electric Activity

Fidani

2011

Geosciences

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A network of low frequency electromagnetic detectors has been operating in Central Italy for more than three years, consisting of identical instruments that continuously record the electrical components of the electromagnetic field, ranging from a few Hz to tens of kHz. These signals are analyzed in real time and their power spectrum contents and time/frequency data are available online. To date, specific interest has been devoted to searching for any possible electromagnetic features which correlate with seismic activity in the same region. In this study, spectral analysis has evidenced very distinct power spectrum signatures that increased in intensity when strong seismic activity occurred near the stations of the 2009 L'Aquila earthquake. These signatures have revealed horizontally oriented electric fields, between 20 Hz to 400 Hz, lasting from several minutes to up to two hours. Their power intensities have been found to be about 1 µV/m. Moreover, a large number of man-made signals and meteorologic electric perturbations were recorded. Anthropogenic signatures have come from power line disturbances at 50 Hz and higher harmonics up to several kHz, while radio transmissions have influenced the higher kHz spectrum. Reception from low frequency transmitters is also provided in relation to seismic activity. Meteorologic signatures cover the lower frequency band through phenomena such as spherics, Schumann resonances and rain electrical perturbations. All of these phenomena are useful teaching tools for introducing students to this invisible electromagnetic world.

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Section: Introductionmentioning

confidence: 99%

The Central Italy Electromagnetic Network and the 2009 L'Aquila Earthquake: Observed Electric Activity

Fidani

2011

Geosciences

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“…These events were followed some tens of hours later by local creep events at site 4.5 km away. BREINER and KOVACH (1967) suggested that the magnetic and creep events were both generated by stress changes at depths of about 10km.…”

Section: Transient Eventsmentioning

confidence: 99%

“…The fact that the magnetic properties of various crustal rocks are sensitive to stress leads to the possibility of using magnetic measurements to monitor crustal stress. Attempts to observe such phenomena, known as tectonomagnetic events, have met with some success (BREINER and KOVACH, 1967;SMITH and JOHNSTON, 1976;DAVIS et al, 1980;RIKITAKE et al, 1980;SHAPIRO and ABDULLABEKOV, 1982). However, the most easily identified tectonomagnetic event (i.e., the coseismic change expected to accompany rup- Improved resolution, particularly at high frequencies, may allow these measurements to be made.…”

Section: Introductionmentioning

confidence: 99%

A comparison of proton and self-calibrating rubidium magnetometers for tectonomagnetic studies.

Ware

Johnston

Mueller

1985

J. geomagn. geoelec

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A network of 27 proton magnetometers (PM's), designed to detect stress related magnetic events of crustal origin, has been operating near active faults in California for the past decade. We present here comparative magnetic difference field data from PM's used in this net with that obtained from new selfcalibrating rubidium magnetometers (SCR's). The instruments were first compared over a 50-m baseline in an aseismic and magnetically quiet region in Colorado. For PM's having either a 0.25-nT or a 0.125-nT least count, the observed difference variations were 0.2-nT and 0.17-nT rms, respectively. For SCR's having a 0.001-nT least count and a 100-second averaging interval, the difference variation was 0.002-nT rms. Power spectra of these data indicate that the noise for the PM's is close to their least count limit. However, the SCR noise decreases at about 20 dB per decade until it approaches its least count limit 40dB below the PM limit, for periods less than 30 minutes. A similar experiment was conducted using collocated SCR and PM pairs separated by 13km along the San Andreas fault. Power spectra indicate that both systems are equivalent and are dominated by external noise at periods greater than 4 minutes. Below 4 minutes the PM noise approaches its least count limit while the SCR noise continues to decrease at about 20 dB per decade until it is 20 dB below the PM limit at a period of 30 seconds. Improved discrimination of magnetic transients caused by fault activity with periods of several minutes to perhaps an hour appears to be possible with higher sensitivity magnetometers.

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“…Such investigations include, 1) the search for field changes that may be associated with fault movements (STACEY, 1962;BREINER 1963;BREINER and KOVACH, 1967;, 2) investigation of piezomagnetic effects associated with changes in the state of stress within geological structures (WILSON, 1922;BARSUKOV and SKOVORODKIN, 1969;HASBROUCK, private communication, 1969), and 3) measurement of the decorrelation of magnetic field variations at nearby locations due to differences in geology or other effects (STACEY and WESTCOTT, 1965;MOSNIER, 1966;RIKITAKE et al, 1967OSGOOD, 1970). So far proton-free-precession magnetometers, optically pumped rubidium vapor magnetometers with very narrow lines (UNTERBERGER, 1960), and the optically pumped potassium vapor magnetometers developed in France by MOSNIER (1966) have come closest to filling the need for high accuracy.…”

Section: Introductionmentioning

confidence: 99%