Earthquake Pre-detection

Earthquake prediction or perhaps more precisely earthquake forecasting is something that still eludes scientists. Despite some well-known successes, the failure rate of earthquake forecasts is still extremely high – even from the clairvoyants who claim knowledge of an event from time to time.

The groundwork which will enable more accurate scientific earthquake forecasts is being carried out by seismologists worldwide. They are already able to indicate that certain areas are at a higher or lower risk of experiencing an earthquake, based on studies of previous events.

Earthquake catalogues for New Zealand have been compiled from historical records, studies of known earthquake faults and, in more recent times, instrument recordings. Seismologists are now studying these catalogues, looking for patterns such as foreshocks which might give warning of a coming larger event and the cyclic nature of previous earthquakes. The significance of earthquake swarms, periods of frequent earthquakes and the role of quiet periods is also being studied. Scientists are also monitoring the build-up of stress in the earth as plate and fault movements occur, in the hope that they can detect when the strain has to be released in an earthquake.

A news item in a programme for radio buffs broadcast on WorldFM caught my attention yesterday. The briefly mentioned item on “This Week in Amateur Radio” reported that radio signals had been detected prior to some of the larger recent earthquakes. This alerted me to two recent studies.

The first involved the study of Very Low Frequency pulse (VLF) signals in the 1-10 kHz range that were emitted days prior to earthquake events. The challenge facing the Japanese scientists studying this effect, is that lightning also causes pulsed radio transmissions in this frequency range and at a far higher rate.

The second study involved a drop in the background level of radio frequencies (RF) days prior to an earthquake. A device which converted the RF signal from an aerial to direct current was connected to a monitor. The device was effectively measuring the combined effect of signals from broadcast and other radio stations as well as noise generated by vehicle ignition systems, computers, TV sets etc. For some reason, it appeared that radio propagation was reduced by some effect days prior to an earthquake.

Several explanations for these effects have been put forward, but further research is required. It is known that the compression of rock as the strain builds up prior to an earthquake causes small anomalies in the local magnetic field and this may affect radio propagation. It is also known that crushing of rock causes energy to be released in the form of heat and electricity, and perhaps RF signals are emitted at some point in the process.

So. Why a couple of days before an earthquake? Completely separate studies back in the 1960s detected an effect called dilatancy which occurs as rock is squeezed when strain in a region builds up. As pressure builds toward a rupture, the rock becomes temporarily stronger as cracks form and fluid content changes. Propagation rates for vibration from distant earthquakes also change in the region affected until things return to “normal” after the rock fails and an earthquake occurs.

All of these observed effects occur at different times before an earthquake, but seem to be different parts of the process.

This work in detecting events leading to an earthquake is effectively pre-detection, and is an essential step on the way to more accurate forecasting.

One Response to “Earthquake Pre-detection”

  1. Paul Doyle says:

    very early one morning at 12.02 am was in the lounge watching TV. I noticed my gold fish acting strange. They bunched into corners and swum rapidly between each end of the tank. I was so intregged I watched them for about 20 seconds and went back to the TV. About 12.03 an earthquake struck. I checked the fish to see them engaging in their usual swim manner.
    My flatmate was a B Tech(Chem)student who had a cage with 2 buggies in it. I told him of the fish behaviour and said his birds woke him at about the time I first noticed my fishes behaviour. He thought a cat was in his room. He went back to sleep and was asleep at the time the quake struck. He did howvere remeber the time the birds played up. Seems strange but at a push I say these animals detected some thing that gave about 30 seconds warning of the quakes arrival. Any other explination would be intersting. I have had fish for about 15 years and have never seen this type of behaviour before or since.

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