Earthquake Warning
March 27, 2012
I wrote about
earthquake prediction in a
previous article (Earthquake Prediction, February 18, 2011). People in
antiquity looked to signs, such as changing
water levels in
wells and unusual
animal behavior as
earthquake precursors. The advent of
science and technology has us looking at
radon dissolved in well water, changes in the
electrical noise caused by the
piezoelectric effect in rock under stress; or,
fractoluminescence, in which the
electric fields caused by separation of
mineral crystal planes will generate light.
Since a chance observation by Antony Fraser-Smith, an
electrical engineer at
Stanford University, that the
Loma Prieta earthquake in 1989 produced high intensity
ULF radio signals in the days prior to the quake,[1] there's been much research on using ULF radio as an earthquake predictor.
Remote sensing by
satellites has been researched, also. The
Demeter (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) microsatellite has revealed a strong
correlation of low frequency
electromagnetic activity and
seismic activity.[2-4]
Decades ago, I'm certain that
scientists were as confident in finding a good means of earthquake prediction as they were in putting a
man on the moon. Earthquake prediction has been elusive, so much attention is now drawn to earthquake warning, instead. A good model for this is the
tsunami warning systems that have been enhanced since the devastating
2004 Indian Ocean earthquake and tsunami and the
2011 Tohoku earthquake and tsunami.
Although earthquakes travel much faster than tsunamis, their speed is not instantaneous. It's physically limited by the
speed of sound in solids, which is a few kilometers per second. A good estimate of earthquake
propagation speed is 4 kilometers per second (2.5 miles per second). In most cases, this gives at least a few seconds warning to a lot of people.
For example, the
1994 Northridge earthquake had an epicenter in
Northridge, California, which is about twenty miles from downtown
Los Angeles. Damage from this earthquake occurred up to 125 kilometers (85 miles) away.
Poor Louis!
Louis Agassiz statue, Stanford University, after the San Francisco earthquake of 1906.
Louis Agassiz is known for his theories of the ice ages, but also for his resistance to Darwin's theory of evolution.
(Via Wikimedia Commons).[5)]
In the past, such warnings might have been given by
siren signals, such as the systems in place at
Indian Point, near
New York City, and the
Diablo Canyon Power Plant, in an isolated area between
San Francisco and
Los Angeles. In the case of Indian Point, the system has more than 150 pole-mounted warning sirens, which cover just a 10-mile radius around the plant. An effective siren system for a wide area earthquake warning system would be very expensive in construction and maintenance.
At this time,
Japan,
Mexico,
Taiwan,
Turkey and
Romania have earthquake warning systems.[6] In these systems, the
sensors are set to detect the faster
P-waves that presage the destructive
S-waves. The Japanese system uses a thousand
GPS-enabled sensors in
boreholes that are set about a hundred
meters in the ground in its billion dollar system.[6]
Detection of the quake itself is technologically very easy; as outlined above, it's the warning system that's hard.
Mexico City, which is more than a hundred miles from a typical earthquake
epicenter, has a siren warning system,[6] but today's era of
cellphones and
smartphones makes possible a very direct, almost instantaneous, personal warning system. Such a system is being researched for earthquake-prone
California.
The California plan, as outlined in an
LA Times article,[6] is to use
social media systems, such as
Twitter, along with conventional
broadcast radio and
television messages, for the warning system. Even a short alerting time will allow certain precautions, such as slowing
trains and opening
fire station doors.[6] In a plan that's reminiscent of the
SETI@Home project, scientists intend to enlist public support in attaching
accelerometers to their
home computers, our enabling applications that utilize the accelerometers on their
mobile computing devices, to send data to a central station.[6]
Although California is an obvious candidate region in the US, it seems that we're seeing earthquakes in areas in which earthquakes are rare. There was a recent event in
Wisconsin,[7] and last year's, August 23, 2011, 5.8-
magnitude earthquake in
Virginia that I felt at my
New Jersey house. Once the messaging infrastructure is in place, such a system could be used for warning of other emergencies, such as
tornados.
References:
- Scientists debate new evidence for electromagnetic earthquake predictors, Stanford University News Service, December 31, 1991.
- F. Muto, M. Yoshida, T. Horie, M. Hayakawa, M. Parrot, and O. A. Molchanov, "Detection of ionospheric perturbations associated with Japanese earthquakes on the basis of reception of LF transmitter signals on the satellite DEMETER," Natural Hazards and Earth System Sciences, vol. 8, no. 1 (February 26, 2008), pp. 135-141.
- A. Rozhnoi, M. Solovieva, O. Molchanov, P.-F. Biagi, M. Hayakawa, K. Schwingenschuh, M. Boudjada, and M. Parrot, "Variations of VLF/LF signals observed on the ground and satellite during a seismic activity in Japan region in May-June 2008," Natural Hazards and Earth System Sciences, vol. 10, no. 3 (March 16, 2010), pp. 529-534.
- M. Athanasiou, G. Anagnostopoulos, A. Iliopoulos, G. Pavlos and K. David, "Enhanced ULF radiation observed by DEMETER two months around the strong 2010 Haiti earthquake," arXiv Preprint Server, December 7, 2010.
- You can see a photograph of Agassiz in a previous article (Screech!, November 17, 2011).
- Hector Becerra and Sam Allen, "California struggling to prepare quake early warning system," LA Times, March 22, 2012.
- Helen Thompson, "Experts sound off on Wisconsin mystery quakes," Nature News Blog, March 23, 2012.
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