Earthquake Science 101
By now everyone knows that earthquakes are caused by a rumbling deep inside the earth and if the rumbling is severe enough, there is damage here on the surface. The amount of damage depends on several factors including the type of quake, and location. Most folks look for a measure of intensity from the newsperson; “There was a quake last night in Outer Slobovia which measured 6.2 on the Richter Scale.” We know that was a quake of moderate strength. The higher the number, the more intense the quake, thus the more danger to life and property..
In 1935 Charles Richter developed a scale based on seismographic readings to measure the intensity of earthquakes. For several decades his scale was the state of the art for earthquake measurement. But technology being what it is, the Richter magnitude scale eventually became obsolete, mostly because of its limitations in accurately measuring the quake several miles from the epicenter. Then one of his peers improved on the original and it became the Modified Richter Scale. Again technology drove the geology community to improve and along came the Mercalli scale.
While the Modified Richter Scale is still used to measure the intensity of the quake, the Mercalli Scale is used to measure the effects of the quake. The effects are varied, compared to the distance from the epicenter. Then to further complicate matters, in the 1970s, along came the Moment Magnitude Scale (MMS). The magnitude is based on the seismic moment of the quake. A formula involving the rigidity of the Earth, the amount of slip on the fault, and size of the area that slipped, measures the MMS. Fortunately for the layman, the numbers to report the MMS are the same as the Richter Scale numbers.
I realize all this can be confusing, but hang on. Did you know that an earthquake measuring 3.0 is ten times stronger than one measuring 2.0? We are conditioned to break down numbers in tenths. For example a sign reading 6.5 miles, means 6 and one half miles. Not so with the Richter Scale. Using ordinary logic, you’d think a 6.0 earthquake would be twice as intense as a 3.0. Not so, in reality it is three-hundred percent greater!
Scientists can come pretty close with predicting where quakes will happen, but even with all of today’s technology and measuring equipment, it is still impossible to accurately predict when they will strike. Thanks to GPS technology and literally thousands of sensors drilled deep within the earth’s crust, plate movement can be recorded as little as one-half centimeter. Even as you read this, the Cascade Mountains are rising and tilting eastward as the Juan de Fuca plate pushes under the Continental Plate along the Cascadia Fault about 60 or so miles off our coast. Currently they seem to be stuck, but they are still pushing. When they become unstuck, we will have an earthquake that may earn the title, “The Big One!”
Check your supplies and your plan. Now is the time to prepare!
As always, questions and comments can be sent to disasterprep.dave@gmail.com.
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