Haiti aftershock: Why a 6.1 quake isn't that powerful

Christian Monitor ^

[marthemaria]

A magnitude 6.1 aftershock struck near Port-au-Prince on Wednesday morning. With so many buildings damaged by the major Haiti earthquake last week, there are concerns about danger. But there's a world of difference between today's quake and the 7.0 earthquake that did so much damage last week. The aftershock that hit Haiti shortly after 6 a.m. on Wednesday frightened Haitians traumatized by last week's much stronger earthquake and raised concerns that it could bring down buildings weakened by the original earthquake and cause more loss of life. While a 6.1 magnitude earthquake sounds almost as strong as a 7.0 earthquake, the difference of the destructive power between the two is greater than an order of magnitude. Unlike temperature scales, in which units of increase are constant, the method used to measure earthquake magnitudes is logarithmic. What this generally means is that the amount of shaking at ground level caused by a 5.0 earthquake is 10 times less than that caused by a 6.0 earthquake and 100 times less of that caused by a 7.0 earthquake.

[marthemaria]

I became very worried and scared when I read about the new quake. This helped a bit

[KarlInOhio]

While a 6.1 magnitude earthquake sounds almost as strong as a 7.0 earthquake, the difference of the destructive power between the two is greater than an order of magnitude. Unlike temperature scales, in which units of increase are constant, the method used to measure earthquake magnitudes is logarithmic. What this generally means is that the amount of shaking at ground level caused by a 5.0 earthquake is 10 times less than that caused by a 6.0 earthquake and 100 times less of that caused by a 7.0 earthquake.

Huh? A ten times difference is an order of magnitude, thus the difference between 6.0 and 7.0 is exactly one order of magnitude. The difference between a 6.1 and 7.0 is less than one order of magnitude, being only a 7.94x difference.

[KeepUSfree]

No....take the number “50”....ten TIMES greater is 500. Ten “more” is 60.

[KeepUSfree]

Reread your post....never mind....!!! ;-)

[Izzy Dunne]

No....take the number “50”....ten TIMES greater is 500. Ten “more” is 60. Huh?

Ten TIMES greater than 50 is 550.

[KarlInOhio]

But the Richter scale is logarithmic, similar to decibels in sound. Adding one on the Richter scale is the same as multiplying the "shaking" (I don't know if that is total power or amplitude of motion being measured) by ten.

If I create the Karl Scale for your number by using the logarithm, your 50 would be 1.7. One more than 1.7 is 2.7 on the Karl Scale, which is 500 (ten times) of your original measurement. Adding on a logarithmic scale is the same as multiplying on a linear scale.

[Frantzie]

The earthquake in Haiti plus Obama will wipe out one thing -Florida. Haitians and other illegals are turning it into a bankrupt third world state like Calif. Businesses are fleeing as the unemployment taxes have gone up 10 X in the past few months. Haitians are turning Florida into Haiti.

[eclecticEel]

Generally when speaking in order of magnitudes you would round to the nearest power of 10; so that 7.94 = 10.

Try this one on for size: “President Obama has increased the yearly federal deficit by an order of magnitude over his predecessor.”

[Don Corleone]

Musically...."A Whole Lot of Shakin' Goin' on"

[boomop1]

The article is exactly right, same as sound measurement on a log scale.

[KarlInOhio]

If the author had said "almost an order of magnitude" he would have been right. If he had said "an order of magnitude" he would have been imprecise, but close enough for newspaper work with rounding. But saying "more than an order of magnitude" he showed that he really didn't know what an order of magnitude is.

Now don't get me started with misuse of the term "quantum leap".

[joinedafterattack]

This author is CRAZY. We in California can attest that a 6.1 is HUGE. Yes a 7 is much much worse but a 6.1 is massive. Trust me, I have been in two of them.

[altura]

Just read in the loathed and despised Dallas Morning News that Texas may get a new congressional seat as a result of the influx of New Orleans people after the hurricane.

If New Orleans is so great and magical, how come nobody wanted to go back?

Well, they didn’t. Increasing the population and crime rate of Houston, not to mention the poverty and welfare rate.

Looks like the same thing may happen to Florida.

[paterfamilias]

This is yet another example of the basic scientific illiteracy of the press.

Why use the clumsy “10 times less” when “one tenth as strong” would be both accurate and more informative?

Also, I agree that this reporter does not really seem to understand that “by an order of magnitude” means “by a factor of 10”

I don’t know about you, but 1/10 the power of the quake that levelled Haiti still seems mighty powerful to me.

[RnMomof7]

I heard a scientist on TV today say that after shocks are usually about 1 magnitude below the original

[bobsatwork]

OK. So a 6.1 is much less than a 7.0. But a 6.1 ain't small. I was driving my car in Pasadena, CA when a 5.1 hit (in the 1980’s). It felt like I just had a front-tire blowout, in fact, that is exactly what I thought happened. I pulled over and got out of the car when an aftershock hit with enough force that I held onto the car to steady myself. The aftershock was a 4.5. (overall there was pretty minor damage, mostly broken glass in Arcadia)

[Lonesome in Massachussets]

According to Wikipedia, the Richter is log base 10 of the magnitude of the (RMS?) displacement. They claim that the energy released is proportional to the 3/2 power of displacement, so a difference of one on the Richter Scale is a factor of 10 in displacement, but 31.6 in energy.

Too subtle for a general purpose news report, I suppose. I imagine that it’s not just the energy but the spectrum that contributes as well and local construction standards determine the actual damage.