Tikalon Blog by Dev Gualtieri

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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.

Louis Agassiz statue, Stanford University, after the San Francisco earthquake of 1906

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 .

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