Chile Earthquake - How bad?

Some news reports have state that this weekend’s earthquake was hundreds of times worse than the Haiti quake, but some have said that the Chile quake was almost a thousand times worse. I am sure I fail to understand the Richter scale and the geologic forces at work, can anybody explain how much more force or energy was released during the Chile quake?

BTW - You should see a room full of lawyers trying to figure this out. Math was not a skill present in the room.

I heard on the news this is the 5th strongest earthquake ever recorded since they started recording earthquake strengths.

It was much more powerful than the Haiti earthquake (8.8 versus 7.0 which is a lot stronger) although it caused less damage partly because it was further away from any major cities than Port au Prince (Haiti’s main city) was, the earthquake was also much deeper (IIRC 20 miles versus 12 miles down). Add to that Chile has better building codes than Haiti does so, while not perfect, they can ride an earthquake out better than Haitians can.

The Richter/moment magnitude scales are not exactly linear, because the energy release of an earthquake (how much damage it is capable of doing) is not proportional to its shaking amplitude (ie., what we use to measure its size). Each full integer is ten times bigger than the last - so a earthquake measuring 8.0 is ten times larger than one measuring 7.0.

The Haiti earthquake was a 7.0, and the Chilean earthquake was an 8.8. That means it’s a bit less than one thousand times the magnitude.

The Ricter scale is logrithimic, so an increase of one on the scale is a factor of ten larger in terms of the actual energy of the quake.

so 10^(8.8-7.0)=60. The Chilie quake was 60 times more powerful then the Hatiain one, though as the previous poster mentioned, other factors kept it from being equally destructive.

Googling the phrase [Chili quake “times more powerful” Haiti] reaffirms my belief that the news media is not very good at math.

Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released.

http://earthquake.usgs.gov/learn/faq/?faqID=33 This page has the formulas to calculate the energy released and the equivalent amounts of TNT and nuclear bombs. It is a wealth of information about earthquakes for any educational level.

With a sister living in Southern California, and a son who has lived in Japan before and is going back to Japan in June, this website is in my favorites menu.

You left out a step - it’s 8.8-7.0 x (10^2)(^3/2).

ETA: Actually, that’s not right either. It’s [10^(8.8-7.0)][^3/2].

((10^8.8 - 10^7.0) / 10^7) = 62.1

I’m a crappy mathematician, but I get 62.1 times more powerful.

I got 501.19 times.

Given the spread of disease in and around Port-au-Prince, it may even be the case that, on the day of the Chile earthquake, more people still died as a result of the Haiti earthquake than the Chile earthquake.

Seismologists use two different scales to measure earthquakes. According to the famous Richter scale, which measures absolute energy released, the Chilean quake was 8.8 compared to Haiti’s 7.0 – 500 times more powerful.

However, there is also the Mercalli Intensity Scale, which measures the quake’s power according to actual structural damage and how intensely it was felt by humans. Using this scale, Chile measured Level VIII (Destructive) while Haiti was much greater at Level X (Disastrous). It’s a subjective measurement, but much more accurate in assessing human impact. Also, Chile is a much wealthier country than Haiti, with stricter building codes, skilled emergency teams, and a population who are accustomed to strong quakes and know how to ride them out.

How are some of you getting that a 8.8 is between 500 and 1000 times stronger then a 7.0.

Starting with a 7.0, an 8.0 would be 10x as strong, and a 9.0 would be 100x as strong. Any answer given that is over 100x has to be wrong, correct?

A 7.0 has 10x more ground movement than a 6.0 but it has 32x more energy.

I suspect that is where the confusion is.

The wikipedia site on moment magnitude actually shows how to compare two different earthquakes, using these two as an example: Moment magnitude scale - Wikipedia

It comes up with about 500x stronger, which is also what I’ve heard on the news.

In addition to the factors like building construction, etc, that have been mentioned, one other thing to keep in mind is that Richter magnitude is based entirely on shaking intensity at the surface, whereas the moment is based more on the geophysical characteristics of the earthquake (specifically it’s the ratio of the stress and strain in the rock times the amount of slip on the fault times the area of the slip, all of which can be deduced by global P and S wave arrival times).

This gives a better indication of the total energy released in the earthquake, but since not all of the total energy turns into seismic energy, the moment magnitude is not necessarily directly correlative to what the intensity is going to be on the surface, and especially deep earthquakes may be very high intensity but not felt as much on the surface.

victory dance

Thanks to everybody for the help. I am going to prep this info and brief my department on your findings. Why? Because our staff meetings stay on topic for slightly less than half a second. This has nothing even vaguely related to our day-to-day work. I do love the people I work with.