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| Titel |
The Pulse Azimuth effect as seen in induction coil magnetometers located in California and Peru 2007–2010, and its possible association with earthquakes |
| VerfasserIn |
J. C. Dunson, T. E. Bleier, S. Roth, J. Heraud, C. H. Alvarez, A. Lira |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 11, no. 7 ; Nr. 11, no. 7 (2011-07-29), S.2085-2105 |
| Datensatznummer |
250009576
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| Publikation (Nr.) |
 copernicus.org/nhess-11-2085-2011.pdf |
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| Zusammenfassung |
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. |
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