15 Jun 2011

How big can an earthquake be?

Last month, a few people thought the world was going to come to an end. There was not scientific basis for their worry whatsoever, but still they raised a few eyebrows.

In one Toronto Star article (that the Star did not share online), geophysicist Qinya Liu discussed ways in which the world, or at least human existence, could come to an end—and systematically ruled them out. Her reasons seemed plausible. We'd know if a meteor the size of the moon were on a collision course with the earth. The biggest volcanic eruption in human history left 10,000 people alive to repopulate the planet (rather successfully, too!). Nuclear weapons have been around for half a century and we're no more likely to use them now than ever before. Alien invasions are the stuff of bad summer movies, not reality (so far). A big enough earthquake isn't possible.

That last one caught my attention. We just saw widespread destruction in Japan from a massive 9.0-magnitude earthquake. That's among the most powerful earthquakes in history and it struck a densely populated area. The carnage was terrible, and more than 15,000 people died. Still, that's nowhere near wiping out all of humanity.

Is there a maximum magnitude for earthquakes?

Earthquake damage to store, California 2010.
Source: FEMA
Even in science fiction, wiping out the human species takes at least a 10.5 earthquake. Nobody knows what it would really take. But why is an earthquake with a magnitude above 10 impossible?

First, you have to remember that the scale we use to measure earthquakes is exponential. A 4.5 is ten times bigger than a 3.5. That means a 5.5 is 100 times bigger than a 3.5.

I remember a 4.5 quake on Vancouver Island that woke me up one morning. It felt like someone was jerking my bed and sounded like a tractor trailer was going through the garden. A 10.5 quake would be one million times more powerful. One million. The biggest quakes in history top out around 9.5, and that's only 100,000 times more powerful. A world-destroyer would have to be at least one-million times the strength of the quake that shook me awake that morning!

It takes a lot of energy to make continents move like that. But if they can hit 9.5, why not 10 or 10.5?

For an answer, I turned to Stephen Johhston, a geology professor at the University of Victoria who specializes in earthquakes in subduction zones (where one plate goes under another—it's where the biggest earthquakes occur and most mountains form). He said it has to do with how strong the rocks are.

"Earthquakes occur when rocks break in response to a buildup of stress," he said. "Imagine taking a long, skinny icicle and you start trying to bend it until it breaks. You will not have to expend too much energy before the icicle breaks, because the ice is fairly brittle and 'weak.' But if you took a similarly shaped wooden stick, it would take you considerably more effort to break the stick. In other words, the earthquake you produced by breaking the stick is greater than the one produced by breaking the icicle."

There is a limit to how much pressure rocks can withstand before they break. So they'd break before enough built up to cause a humanity-destroying quake. Most researchers figure that limit is around 9.6, Johnston said.

How deadly is a big quake?

Big earthquakes can be deadly, causing buildings or bridges to collapse and crush people. But most people who die because of a quake aren't killed directly by the shaking of the ground. Sometimes earthquakes can trigger deadly landslides. But the real carnage comes from tsunamis. These are huge waves, sometimes higher than a house, that are caused when an earthquake happens under the ocean.

In the Japan earthquake this year, much of the destruction came from tsunamis. And earlier this decade, deadly tsunamis killed more than 100,000 people around the Indian Ocean.

Because the big earthquakes, those above 9.0, happen in subduction zones, they tend to happen under water. The shaking can cause big destruction on land, too, but the greatest risk is to people who live in coastal areas.

In other words, even the biggest earthquake possible simply could not kill all the people on Earth.

Craig Saunders is a writer, editor and author of What is the Theory of Plate Tectonics? (Crabtree, 2011). He lives in Toronto.

13 comments:

Jim Pettit said...

This is obviously an extremely rare event, and if it happened the resulting quake would be pretty far down the list of things to worry about, but is there a limiting magnitude on a quake caused by something other than tectonic stress--namely the impact of a comet or asteroid? Using some of the various online calculators, the largest simulated quake I could produce is an 11; is that due to limitations with the software, or is anything over 11 simply not possible because the earth would be pulverized with the release of so much energy?

Anonymous said...

When I was a kid,I learned in high school that an earthquake could never rate higher than somewhere around 6.0. It's changed since then because scientists have learned more. I think scientists in any field should keep a more open mind than they appear to have when they publish.

Anonymous said...

"When I was a kid,I learned in high school that an earthquake could never rate higher than somewhere around 6.0. It's changed since then because scientists have learned more. I think scientists in any field should keep a more open mind than they appear to have when they publish."

No. No, no no. The Richter scale was developed in 1935 and was able to be back dated onto various earthquakes to get good estimates of large quakes over 8. So unless you are like 100 years old then your teacher must have been an idiot

Anonymous said...

Neat information.

AstralWriter said...

The Chile quake that registered above a 9.0+ actually knocked the Earth off its axis. It is nothing we could feel or measure because this is too little. However, the force of this massive quake would pulverize any American city.

Look at the destruction the Northridge earthquake brought on in 1994. A 6.7 magnitude decimated Southern California.

A 11.0 would resemble the quake depicted in the 2012 movie. It would send coastal cities into the ocean. Total destruction. The jolt could be felt thousands of miles away. Some scary stuff.

I believe a comet and/or asteroid would do some major damage.

Cohen Rice said...

That would be scary:/ Well if a comet/asteroid hit we would know but yeah it would be scary and it is a possibility every day on earth but I hope it would be faster then the pain .
I've always wondered and pondered about what it would be like after death and all those who came before us . Im not sure about what is after death as no one knows and I think about a appending natural disaster or any disaster everyday I use to have a anxiety about it but not anymore I still am scared of death and the fear if the unknown but now I know its apart of life and has always been . I don't neccesairly believe in Christianity or any other religion at all . I wouldn't consider myself an atheist because I do believe that there is a creator I call (The Creator) which is equivalent to everyone's religion as what they refer to as God and various other ways in different religions. I'm from the U.S and my family is mostly all Catholic or Christian don't really know the difference since its pretty much similar and of course. I don't believe any religion is right or wrong but everyone is always constantly fighting and arguing over which religion is right and who's to say the Christianity is right compared to the religions around the entire world I believe that they were made to give hope and teach morals to people which clearly have worked and some haven't but I'm not saying they are wroung. I believe in something but just that they're is a creator who created life and life was created by the elements that were needed to form life as we know it thus the creators of the stars which I'm pretty sure are gasses and other various elements which were created by something . I don't want to believe that there is nothing and we magically were just formed and were created out of some extraordinary evoulution I want and will continue to believe that they're is something and that all life goes onto after . The universe is full of mystery and still to this day so many theories on how it came to be . I'm barely 18 and yet I think about this shit everyday and wonder about when will be the day I pass on alone and or a fatal catastrophe which brought me to this site and literally read this from top all the way to the comments . I'm always told I'm overthinking by my family I'm not living my life everyday in fear about this but it crosses my mind everyday and the beggining of the day and at the end and it middle after I'm done with social things . I don't know why I'm pouring my thoughts onto the site and if its even being read but if you have or are reading this thank you for your time . I love astronomy and everything about it and it fascinates me more then social life does but of course I have to focus on my life in order to live in this economic based world. Thank you for your time and for reading this and to whatever happens to anyone on this planet cosmic or domestic (planet wise) may we all find something on the other side that is bliss and warmth. Life is short to live in pain and sadness . Thanks again and yes I know this is a Earthquake link site I was looking up possible earthquakes and sizes ones can reach up too . I live in California and I feel that we are definitely due for a huge one possibly huger then Japans . I have many questions for those on this site who are willing to answer and reply if I haven't wrote enough haha well Goodbye for now or forever . I have looked up so many things that are possible raging from cosmic catastrophes all the way to mega volcano's and mega tsunamis . I have yet to expierence anything in my life time since I am 18 and worry that maybe I will now that its the 20th century going on 2015 . Ok may you all have a goodnight/day.

Anonymous said...

A 4.5 is actually 30 times more powerful than 3.5. The current ratings for earthquakes are measured on the Moment Magnitude Scale (in which each full measurement is 30x more powerful than the prior). The richter scale hasn't been used since the late 1970's.

Anonymous said...

The Chicxulub impact which killed the dinosaurs (while not an earthquake) had an equivalent magnitude to 13 approximately. Mind you, much like a nuclear explosion (or in this case, a million nuclear explosions) - most of this energy was absorbed by the planet.

Earthquakes in comparison occur along fault lines. A Mw10 earthquake would only be possible along a subduction zone, with estimates requiring a fault line as long as the entire pacific subduction zone to longer than the circumference of the earth.

A Mw11 earthquake would likely tear the earth in half. A Mw12 Earthquake would likely pulverize the planet to dust.

A Mw23 starquake was recorded in 2004 from SGR 1806-20, a magnetar 50,000 lightyears from earth (about half our galaxy away on the other side of the central galactic core). This quake partially ionized our atmosphere, buckled the magnetosphere, temporarily blinded satellites, and released as much energy as our Sun does in 250,000 years all in the space of 7.5 seconds. If this quake had occured 10LY away, it would have been an ELE, and would have likely stripped Earth of its atmosphere (or worse).

Rabbitbait said...

Even a 6.3 can devastate a city - here's a link to the centre of Christchurch City in New Zealand. It's five years after the quake that happened directly under the city - the blank spaces are where buildings have been demolished and there a still a heap waiting demolition.

https://www.google.co.nz/maps/@-43.531821,172.6368299,555m/data=!3m1!1e3

We were a victim of a trampoline affect, that caused the land to work in a way similar to when your sibling jumps on a trampoline in a way that makes you go flying. Not fun. That's what happened to our buildings. So, smaller earthquake, but it caused the 3rd most expensive (by insurance company spend) disaster in history.

Bill Chaffee said...

I believe that each increase of one represents an increase of the square root of a thousand in the amount of energy released, so an increase of two would represent an increase of one thousand in the amount of energy released. However the amplitude of the quake would increase by a factor of ten for each increase of one. There seems to be a maximum amplitude for an earthquake. Above a certain magnitude the amplitude doesn't increase but the area over which that amplitude is felt increases.

Sean Black said...

Earthquakes was a tremble happened in the earth's crust. The impact can be so disastrous because of that. The larger it is, more damage it will be. However, in these days, people do not care about natural disaster. The same happened in the most prone earthquakes locations. They just were not aware of the risks if they live in earthquakes zones. The sooner people realize the danger of earthquakes, the better people will prepare themselves.

Eric Archambault said...

Quite amazing is the energy and destruction but yet has a way of fascinating at the same time , such as the sun being 93 million miles away but yet we feel its energy at 100°F !!
Not to mention is the closest star i think and one of the smallest .. Just take star matter and density at just 1 tablespoon weighs 1 billion lbs ~ or so .. . We are just a spec that barely registers on the molecular scale, subject drifting 💤💤👁〰😩 i often wonder if our minds produce our environment , meaning are we just solo and all of this somehow imagined ?? Sorry im rambling here , , good day ..

Gay Person said...

An 11.0 earthquake would rip the earth in half!