Did you feel the earthquake on Saturday, April 20th just before 7:00 a.m.?
We certainly did here on the Steele Line: the bed shook, while glasses and plates rattled in the kitchen cupboards. The epicentre of the quake, which measured 5.5 on the Richter scale, was Plattsburgh, New York. Its effects were felt as far north as Ontario and Québec.
Of course, the quake prompted me to do some research, and here are the results of some Internet searches.
1. Definition
The National Resources Canada site informs us, “Earthquakes are caused by abrupt motions of rocks separated by a geological fault. These motions generate vibrations that can be felt, and, if sufficiently strong, can cause damage to houses. An earthquake generally begins with a sudden noise, or roar, and is followed by vibrations or a swaying sensation. Although vertical movement (up and down) can occur, the horizontal movements (side to side) are those that generate damage. The vibrations can last for mere seconds or for several minutes, depending on the size of the earthquake and the distance from the epicentre.” (www.seismo.nrcan.gc.ca/prepare/eqresist_e.html#The Site Factor)
The Ottawa region is geologically renowned and one reason is because the Ottawa Valley is actually a rift valley. We live on a fault plane and some scientists describe the capital as resembling the hub of a wheel, whose spokes are fault lines. One fault line runs along the base of the Eardley Escarpment, the southernmost boundary of Gatineau Park. Another “ray” of fault lines bisects Gatineau Park and is most easily “seen” in the east-west “line” of lakes situated at the northern fold of the Eardley Escarpment. Look on a map and you’ll see that Philippe, Mousseau (Harrington) and Meech lakes are in a line.
2. Richter Scale
The best definition I found of this method of measuring the magnitude of an earthquake is at wwwneic.cr.usgs.gov/neis/general/handouts/richter.html:
“Seismic waves are the vibrations from earthquakes that travel through the Earth; they are recorded on instruments called seismographs. Seismographs record a zig-zag trace that shows the varying amplitude of ground oscillations beneath the instrument. Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world. The time, locations, and magnitude of an earthquake can be determined from the data recorded by seismograph stations.
“The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.
“At first, the Richter Scale could be applied only to the records from instruments of identical manufacture. Now, instruments are carefully calibrated with respect to each other. Thus, magnitude can be computed from the record of any calibrated seismograph.”
3. Reporting a Quake
Want to know how you can assist scientists in collecting data about earthquakes? If you feel an earthquake, Natural Resources Canada wants to hear from you. Go to their website at www.seismo.nrcan.gc.ca/survey/intense_e.html and fill in the questions. Want to report a quake or find out more, but you don’t have Internet capacity? Contact them at: Geological Survey of Canada, 1 Observatory Cres., Ottawa, Ontario, K1A 0Y3.
Why is this information important? “The information you provide on your experiences of the earthquake will be used to determine the intensity of the earthquake, which is different from the magnitude . Intensity information provides details on the effects of specific earthquakes and helps us to determine how your area may respond to future earthquakes. Seismologists at the Geological Survey of Canada tabulate the information and release intensity reports for significant events. One such report was released for the magnitude 5.9 earthquake in Saguenay, Quebec in 1988.”
For further information: Internet site www.nrcan.gc.ca/nrcanonline/hazards_e.html offers more links and information on other natural hazards.
My personal observations.
Outside, our two horses Whiskey and Drum dashed about in their paddock wildly for a couple of minutes during and immediately after the earthquake. Roughly 10 minutes after the tremors were over, I brought the two animals into their stalls and fed them. The plan was to go for a ride after breakfast. But, when Eric and I went to groom them and tack them up, both animals were clearly distressed: their muscles were spasmodically trembling. After grooming them for a minute or two, we decided to turn them out in their paddocks and ride later as they were too “antsy”. When we brought them in later in the day, they were fine, and we went out on an hour’s ride with no problems whatsoever.
My horse anecdote brings up a question: do animals sense earthquakes and their before- and after-shocks before human beings do? All I know is that there is a body of anecdotal “evidence” which seems to indicate that animals do sense a quake will occur. Can animals be used for predicting earthquakes?
Such questions are fascinating because animals have long been thought to have the ability to detect sensory stimuli which we human beings normally do — or can — not. David Jay Brown’s paper, “Etho-Geological Forecasting: Unusual Animal Behavior & Earthquake Prediction” as published on the Internet, makes a fascinating read on this topic. In it, he writes:
“Perhaps most significantly, on February 4, 1975 the Chinese successfully evacuated the city of Haicheng several hours before a 7.3 magnitude earthquake — based primarily on observations of unusual animal behavior. 90% of the city’s structures were destroyed in the quake, but the entire city had been evacuated before it struck. Nearly 90,000 lives were saved. Since then China has been hit by a number of major quakes that they were not as prepared for, and they have also had some false alarms, so their system is certainly not fool-proof. But never-the-less, they have made a remarkable achievement by demonstrating that earthquakes do not always strike without warning.”
With all the technology we have amassed so far, and with all the seismological data in the world to date, we human beings still cannot accurately predict earthquakes. Can animals assist us to do so? It’s possible. And, it’s another excellent reason to respect our fellow creatures here on Earth.
***
Katharine Fletcher is a freelance writer who telecommutes from her farmhouse north of Quyon — located on the fault below the Eardley Escarpment.