VLF Waves, the Ionosphere, and Earthquakes
There is some intriguing research about whether large earthquakes are
associated with ionospheric changes caused by electromagnetic signals
released by the crushing of rock crystalline structures.
If so, then this might be a mechanism for major earthquake prediction.
One of the primary researchers in this area is Friedemann Freund, of
NASA Ames. He has written several articles introducing
the concept of ionospheric and atmospheric changes as earthquake precursors:
According to Freund,
"Earthquake forecasters can also watch for changes in the ionosphere
by monitoring very-low-frequency (3- to 30-kilohertz) and high-frequency
(3- to 30-megahertz) radio transmissions. The strength of a radio signal
at a receiver station changes with the diurnal cycle: it is greater
at night than in daylight... The altitude of the ionosphere, which moves
lower as the positive holes [positively-charged atoms in stressed rock]
migrate to the surface, also
has an effect on radio signals; the lower the ionosphere, the stronger the
signals. So at dawn on an earthquake day, a curve drawn to represent the
drop-off in radio signal strength will appear markedly different from
the normal curve for that signal at that location."
That is, Fruend believes that
the dawn-dusk signatures will be different for a particular instrument,
perhaps even the signal
strength as monitored during the day, on the day of a major earthquake.
Since the original papers, Freund has made further progress in understanding some of the more
subtle physics underlying the generation of signals prior to major seismic events:
"Those signals may serve as early warning signs.
Of particular practical and theoretical interest is the emission of infrared photons from the ground. These
photons are non-thermal but mix with the 300 K thermal IR emission bands."
Their paper (also highlighted above)
describes some rather unique laboratory experiments demonstrating this stimulated (quantum-controlled) IR emission.
This research is still young and apparently controverial. If there are
effects, they may be too subtle for the SID
instruments to pick up.
If your students do pursue something of this nature,
make sure you make it VERY clear to them that this is extremely early
and tentative research that may or may not provide them any useful results.
If your students do want to explore this, remind them that the epicenter
of a potential earthquake would have to lie somewhere "near"
the line between
the transmitter and their receiver.
(And we have no idea what distances might qualify as "near.")
Thus they would need to track
data from all over the world and, if something irregular were noted,
they would need to triangulate to determine the location of the
potential earthquake. Best approach might be to pick a recent
earthquake then check the SID data from stations around the world
to see if any changes were noticed at, before, or after, that time.
In addition to the 3 above, here are more resource articles you might want
Electrical currents streaming out of stressed igneaos rocks -- A step
towards understanding pre-earthquake low frequency EM emissions
- Seismic Radio
- On the Possible
Origin, Propagation and Detectability of Electromagnetic Precursors of
- Dea J. Y., Hansen P. M. & Boerner W-M. (1993) -
Long-term ELF background noise
measurements, the existence of window regions, and applications to
earthquake precursor emission studies
Phys. Earth Planet. Interior, 77, 109-125.
- Mognaschi E. R. & Zezza U. (2000) - Detection of electromagnetic emissions from fracture
of rocks and building stones under stress; paper presented at
5th International Congress on
Restoration of Architectural Heritage. Florence, p. 553 - 562.
- Warwick J. W., Stoker C. & Meyer T. R. (1982)
- Radio emission associated with rock
fracture: possible application to the great chilean earthquake of May
Geophys. Res., 87, 2851-2859.
Unusual Sunset Terminator behavior of VLF signals at 17kHz
during the Earthquake episode of Dec., 2004
Scientists debate new evidence for electromagnetic earthquake
predictors [note: old report]
- Response of the ionosphere to the Baltic Sea earthquake of 21 September 2004
Anomylous VLF electric field perturbations associated with Chamoli
earthquakes of March/April 1999
Study of ELF/VLF Signatures Associated with Earthquake
Experience of short term earthquake precursros with VLF-VHF
An attempt to delineate very low frequency electromagnetic signals
associated with earthquakes