Have there really been more earthquakes than average?

Update: January 3rd, 2011 – A final update on 2010 numbers posted right here.

chile_eq.jpg

Damage in Santiago, Chile. Photo by Reuters/Marco Fredes

After the massive earthquake this past weekend in Chile, MSNBC published a sensationalistic piece entitled, “Is nature out of control?” The Wall Street Journal asked if three massive earthquakes around the world in two months are related and a cause for alarm. The mainstream media, always searching for sensationalistic or fear mongering news, has latched onto the question; are we seeing more earthquakes than normal?

Well, not really.

To better understand why, let’s take a look at how many earthquakes occur each year on average. The USGS has a fascinating page of earthquake facts and statistics, with the following table:

Magnitude Average Annually
8 and higher 1 ¹
7 – 7.9 17 ²
6 – 6.9 134 ²
5 – 5.9 1319 ²
4 – 4.9 13,000
(estimated)
3 – 3.9 130,000
(estimated)
2 – 2.9 1,300,000
(estimated)

¹ Based on observations since 1900.
² Based on observations since 1990.

For our analysis, let’s take earthquakes based in the magnitude 6.0 – 6.9 range. Why am I picking earthquakes in the M6 range? It’s arbitrary. You can repeat this process for earthquakes of any range. Based on data recorded since 1990, we’d expect to see an earthquake within this magnitude range occur every 2.7 days or so.

So here we are, on March 1st, 2010, the 60th day of the year. How many earthquakes in the M6.0 – M6.9 range have we had this year? According to this handy search tool from the USGS, there have been 25 earthquakes of M6.0 – M6.9 in 2010.

eq_data.png

That works out to roughly one earthquake in the magnitude 6 range every 2.4 days. That doesn’t seem totally unreasonable or a reason for alarm, but we should do some further work to put it in context.

We can plot up the number of earthquakes per year and come up with a standard deviation, assuming a normal distribution of earthquakes in any given magnitude range.

yearly_eq.png


Total results: 21
Mean (average): 2.67143
Standard deviation: 0.41732

So, the number of magnitude 6 earthquakes that we’ve had in 2010 falls within one standard deviation of the mean. If we were to plot up a graph, it’d look like this. The error bars represent one standard deviation.

days_per_M6.png

eqs_per_year_M6.png

Awesome! Well, what about those ranges of values that fall outside of one standard deviation from the mean? For those that don’t understand how statistics works, check out the following bell curve from Wikipedia.

File:Standard deviation diagram.png

This shows roughly the percentage of values that you’d expect to fall within a specific standard deviation away from the mean value.

Dark blue is less than one standard deviation from the mean. For the normal distribution, this accounts for about 68% of the set (dark blue), while two standard deviations from the mean (medium and dark blue) account for about 95%, and three standard deviations (light, medium, and dark blue) account for about 99.7%.

So, if we modify our graph to show an error bar of 2 standard deviations, you’ll notice that every result since 1990 fits inside this model! Statistically speaking, you would expect to find 95% of all results falling within two standard deviations of your average. Simply put, there is absolutely nothing strange happening.

days_per_M6_2stdv.png

In fact, thanks to this normal curve you can basically predict, with a 99.7% chance of success (three standard deviations), that an earthquake of equal to or greater than M6.0 will occur somewhere around the world within the next 3.5 days. Update: Proven correct! A M6.4 earthquake occurred in Taiwan on March 3rd.

Alright, so what’s with all the coverage on earthquakes? It sure seems like a lot is happening, right? We can attribute this to observer bias. The massive devastation in Haiti warranted a large amount of news coverage. Because this is so fresh in everyone’s mind, people are more likely to notice any news or information related to earthquakes anywhere in the world. An earthquake of M6.0 or greater, usually garners international attention.

It’s the same principle that happens whenever you acquire some new toy, gadget, or piece of clothing. Suddenly, you notice that particular item around all the time. It’s like everyone has it.

So, bottom line, the Earth isn’t becoming more active, more dangerous, or even “out of control.” Despite the fear mongering and what esteemed mainstream media networks would have you believe, the simple reality is that the numbers prove things are happening at an expected rate. Keep that in mind the next time a large earthquake happens and everyone is wondering why the Earth seems so active!

Update (April 21, 2010): Chris Rowan at Highly Allochthonous has a great post on yearly earthquake averages and variability with larger magnitudes.

In the last 28 years, there have been on average around 13 such ‘significant’ earthquakes a year, with a magnitude 8 occuring about every year and a half. This average rate is marked by the grey line on the plot: if we extraplolate the six major earthquakes recorded in the first four months, 2010 is on course to experience 18 major earthquakes, a little above average but well within the variability shown by the whole dataset (and it’s actually closer to the centennial average of 16 major quakes a year reported by the USGS above).

46 thoughts on “Have there really been more earthquakes than average?

    1. Don

      I just don’t understand why this report was based on simply the years 1990 – now. That hardly seems scientific. I would better receive one showing stats from say 1800 – now. : )

      Reply
      1. Dave Post author

        Hi Don,

        It’s based on the USGS data which only goes back to 1990. You can see that right here. I believe this is because since 1990, there’s been more data available to collect (e.g., more sensors across the planet).

        Reply
      2. Juliet Dillon

        I agree- but i guess, like weather data, it only goes back so far. Although I would think that they could make some educated guesses based on historic accounts of earthquakes.

        Reply
    1. Dave Post author

      Thanks Ken. It’s something I’m definitely interested in – I was a geologist is a past career. Earthquakes still fascinate me and I absolutely cringe when I see these hyperbolic news reports!

      Reply
  1. Matt

    Don’t you wish more reports were based on facts like this one? Don’t you wish more people understood what all them fancy numbers and graphs meant? While I’m at it; can I have a pony?

    Great analysis!

    Reply
  2. shen

    I really appreciate this, all laid out in facts and graphs. It does feel like there has been more going on than usual, but I questioned it because I also have noticed how much the media loves to build everything up to a frenzy.

    Thank you

    Reply
  3. Dave Post author

    Hah, someone on the Geology News blog was freaking out about how there’s still been a lot of large earthquakes, so I re-ran the numbers as of today.

    Today is March 12th, the 71st day of the year.

    According to the USGS, there have no been 41 M6.0 – M6.9 earthquakes so far in 2010 (Whoa! One would assume that a lot of those are aftershocks from the great Chilean earthquake).

    That means we’ve had an earthquake in the M6 range every 1.73 days. Alright, that number is getting down there. Is it a cause for alarm?

    No. Why?

    The standard deviation is 0.417 days with a mean of 2.671 days between earthquakes of this size (if you’re curious how I got those numbers, reread the article). Since we can expect to find 99.7% of all results within 3 standard deviations of the mean, let’s figure that out. 0.417 x 3 days = +\- 1.251 days.

    2.671 days – 1.251 days = 1.42 days.

    If you start seeing a M6 earthquake more than every 1.42 days, then come talk to me.

    There’s nothing to worry about.

    Here’s the break down for other magnitudes in 2010. If you want to search yourself, you can use this tool:
    http://earthquake.usgs.gov/earthquakes/eqarchives/epic/epic_global.php

    2010 earthquakes:
    M7.0 – M7.9: 3 earthquakes so far in 2010 (yearly average: 17)
    M8.0 – M8.9: 1 earthquake so far in 2010 (yearly average: ~1)

    If you want to account for M7 earthquakes:
    Average: 365 days / 17 eq’s per year = 21.47 days per EQ.
    2010: 71 days / 3 eq’s in 2010 = 23.67 days per EQ.

    Magnitude 8 earthquakes? Average is about 1 a year. We had one.

    Reply
  4. Bill Underwood

    I wrote on this subject a few weeks ago. The elephant in the room that you are not addressing, the reason people care whether earthquakes are increasing is that they know, albeit vaguely, that there’s something in the Bible about earthquakes in the last days. But as I said in my column, Jesus didn’t say earthquakes would increase in the last days. He simply said that earthquakes would be one part of the composite sign of the last days.
    http://www.examiner.com/x-17373-Phoenix-Signs-of-the-Times-Examiner~y2010m3d16-Are-earthquakes-increasing

    Reply
  5. Jill

    Just being lazy here, plus I never was good at math or statistics:

    So how are we doing now? The 7.2 Baja on April 4, and then 7.8 off Sumatra today, April6.

    Bottom line: I will trust you will run a “Time to Freak Out!” post if the shaking level goes off the charts and deviates in a non-standard way.

    Who likes deviates for the most part anyway.

    Reply
  6. Nina Perez

    Thank you for mapping this out! I was also wondering about the stats. I actually don’t watch the news but everyone is talking about them so it does seem to be more than usual.

    Reply
  7. Amy

    Thanks for this thoughtful analysis. It not only helped explain earthquake prevalence but I think I finally understand standard deviation as well now.

    Reply
  8. Ben

    Hi, thanks for this :) Found it because there’s just been another one in China today and it felt like there’s been a lot so far this year. Thanks for the statistics.

    Reply
  9. Michael Teper

    There is another aspect your analysis didn’t address, which is the location of the epicenter. While the quantity and magnitude of earthquakes hasn’t changed, what about the impact on civilization centers?

    Reply
    1. Dave Post author

      That’s an interesting point, but I don’t think it’s indicative of anything. That is to say, I don’t think one can necessarily prove that earthquakes are targeting population centers. It’s the luck of the draw where an earthquake happens and a local population’s ability to prepare for and cope with an earthquake.

      Reply
  10. Brad Fredricks

    Good article, well written and considered.

    I’d like to draw your attention to a USGS infographic, which has since been pulled offline, perhaps for the sensationalist observations that could be drawn from this visual.

    <a href ="http://www.bradfredricks.com/earthquakes%20usgs%20graph08.jpg&quot; title="USGS Graph of Deadly Earth Quakes"

    In the image, you’ll note a MASSIVE uptick in deadly and destructive earthquakes. USGS wisely pulled this offline, clearly its a disturbing trend.

    I’d like to hear your thoughts on this graph, vs the data you’ve pulled. Could you revisit your data, looking at the same information and time frames taken into account in this USGS infographic? Essentially, third party verification.

    Thanks,

    Brad

    Reply
  11. Kirk

    Cool Dave. Makes a lot of sense. I do have one Thought though.
    We, man, are now making earthquakes. At least that is an article in April edition of P.S. is saying. Then we have that nasty fracturing for gas going on, then test drilling into the mantel.
    Ewwwww, are we creating our own disaster movie?

    Reply
    1. Dave Post author

      Yeah, this is something we’ve known about for decades. Specifically, geothermal power production is known to produce small earthquakes due to injected water lubricating the faults. Most of these quakes are between M2 and M3.

      Some have argued that loading caused by the creation of a reservoir (e.g., China’s Three Gorges Dam) might induce earthquakes as well, since the weight of water can significantly alter the distribution of stress on local faults.

      Reply
  12. joe blow

    Rerun your analysis. Now it most certainly is outside the ordinary. At 2.17 standard deviations. Probably just caught it on a statistical fluctuation though.

    Reply
  13. Wayne

    try the analysis again….try it with 5.0 – 5.9 too…current rate for 5.0 – 5.9 is to end 2010 with 2400+ vs a 1320 average. Hmm……everything is perfectLIE normal. :)

    6.0-6.9 on the increase too…also recent China quake 7.1 (Per China) or 6.9?

    Reply
  14. Uriel

    Actually, there has been an increase in major seismic activity from 1973 to 2009 (the years for which there is online information at USGS.gov)

    I was curious, so I took only those quakes of 7.0 magnitude or greater for each year and compared the seismic action on a linear scale (rather than the logarithmic Richter scale). Obviously, there are years of high seismic activity and years of low activity; but, when I ran an OLS regression the slope was +0.97 per year over 37 years. This is the equivalent of one additional magnitude 7.0 earthquake EACH YEAR! Keeping in mind that the quake that recently leveled Haiti was a 7.0 magnitude quake, there are 37 more 7.0 earthquakes per year in 2009 than there were in 1973. That’s significantly more shaking now than in 1973.

    Anyone can do the same analysis that I did and get the same result.

    Reply
    1. Dave Post author

      No, actually there hasn’t been a significant increase in major seismic activity.

      Please read: http://scienceblogs.com/highlyallochthonous/2010/04/the_seismic_non-pocalypse.php

      I thought this point could be best illustrated visually, so I ran a search through the USGS/NEIC earthquake catalogue for earthquakes of magnitude 7 or greater that have been recorded globally since 1973 (the starting point of the database). The results are plotted below. In the last 28 years, there have been on average around 13 such ‘significant’ earthquakes a year, with a magnitude 8 occuring about every year and a half. This average rate is marked by the grey line on the plot: if we extraplolate the six major earthquakes recorded in the first four months, 2010 is on course to experience 18 major earthquakes, a little above average but well within the variability shown by the whole dataset (and it’s actually closer to the centennial average of 16 major quakes a year reported by the USGS above).

      Reply
  15. Adam Green

    I agree that there has been no “extra” siesmic activity, but I do believe the effects for this years earthquakes have been different than in the past.

    My theory is the earth`s mass is trying to move closer to the center of the earth to increase the rotation of the earth , because of the thousands of years of mankind digging from the ground, building ontop of the ground. Thousands of years of kicking dust in the air, we have effectively increased the diameter of the earth making the earth`s rotation to slow down. When our solar system crosses the equator of the milky way the earth WILL be in the same position it was the last time and every time we pass the galactic equator. It`s exactly like the second hand on a clock when it strikes midnight all clock hands are in the same position each time.

    Proof of this was evident in the Chile earthquake, the earth day got shorter by 1 millionth of a sec, that may seem miniscule but if you work that out against the circumference of the earth, it isn`t so miniscule, especially when the indonesian earthquake shortened our day by more than 1 millionth of a sec, i dont know the exact figure.

    Our galaxy is trying to make us speed up so the earth is in exactly the right spot at the right time, and the earth is reacting to it by moving its mass closer to the centre.

    There is a reason the skin colour of our earth inhabitants,dark on on side, white on the other.

    How close to Africa are your gonna be during the main event? Depends what skin colour you want to come out with.

    Reply
  16. carsue

    If you use the USGS tool and indicate a magnitude 2 to 10. Can you explain why from January 1 to July 17…that in 2005 there were 16,944 quakes; 2006 15,509 quakes; 2007 15,237 quakes; 2008 17,211 quakes ….yet in 2009 they are only indicating 8,090 and for 2010 they only indicate 9,676 quakes. How can the activity basically get cut in 1/2 for the past two years?

    Reply
    1. carsue

      Interested wouldn’t you say…

      7+ Greater Earthquakes
      Date
      Range 1/1-8/11 Full year
      2010 16
      2009 10 17
      2008 9 12
      2007 6 18
      2006 8 11
      2005 6 11
      2004 5 16

      Reply
      1. Dave Post author

        Nothing interesting there. As I quoted in my update:

        2010 is on course to experience 18 major earthquakes, a little above average but well within the variability shown by the whole dataset (and it’s actually closer to the centennial average of 16 major quakes a year reported by the USGS above).

        Reply
    2. carsue

      I discovered my own answer to this question….Starting in January 2009, the USGS National Earthquake Information Center no longer locates earthquakes smaller than magnitude 4.5 outside the United States, unless we receive specific information that the earthquake was felt or caused damage. …. However, I still think we are tracking high between the 6.5 and 7.9 magnitude. Will see how the year plays out.

      Reply
  17. nick

    excellent article, very informative. but just wanted to make sure im seeing thing straight. by my count as of today 13th aug. there have already been 17
    M7.0-7.9 events with more then 1/3rd of the year remaining. seems to be trending for a fairly big year. would love to see you rework the numbers again. but look at me making more work for you :)
    cheers!

    Reply
  18. Mimi K

    What about 2011 so far ?? and do you factor in the Tsunami’s that have been happening in recent years? I mean i dont think we ever heard about Tsunami’s up until the 2006 boxing day incident in Asia!
    Would love to have your input about this because i am one of those” worried” people thats beginning to think nature is lashing back at us :(

    Reply
  19. greg

    I know this is an older post… but… 1) we have more instant media coverage, so we see more of it… 2) the world population is increasing so more people are affected by such events.

    Reply
  20. Marc

    Fist of all I enjoyed this post a lot and searched for it because we had to earthquakes here in northern Italy in the past week.
    I’m a nobody and know nothing about anything to do with earthquakes. I love statistics though and find it almost amusing how anyone can say there are more earthquakes than usual. The earth is like a zillion years old and to have records from 1900 till now statistically seen is probably like a milli second. You can’t really claim anything at all. Maybe it’s normal for us to get struck every 50 million years and have it cause an Ice age? Maybe it’s not an average now but it could be once it’s happened 4 or 5 times, who knows.
    Then to say something like god said that there will be lots of earthquakes at the end is a pretty likely assumption whether there is a god or not because even I, the person who is nothing and knows nothing can make a wild guess that at the end of something as big as the planet earth, there shall be a few disruptions!
    Toilets have only been around for a few years theoretically and before that we threw it on the street! We have only just started to measure and record, we all know nothing about anything really. We drink Coke and judge food by it’s packaging knowing nothing about what’s really in it! We buy Sneakers probably made by kids in China and dont really care and what would happen to those poor kids anyway if they had no work!
    What I’m trying to say is, truthfully we know very little, we’re still all idiots and it’s true. SO the question are there more earthquakes than usual can only be answered with, since 1900 no! but what the average is we’ll never know. If there are more than usual, can we change it? No! Unfortunately we can’t and we can’t change anything because we all live our own lives and most of us humans shall never ever ask themselves “Are there” “Is There” “Are we” because they rely on what the news tells them and that’s enough.
    It all boils down to marketing for the most of us, I mean the US is the 4th most dangerous place to live on this planet. But we don’t see that in Baywatch and millions of people want to live there because it’s awesome! Truth is it’s a big dam mess you have 5 billion gangsters that have been expanding from state to state and kill and cause trouble but as long as you don’t have to live there it doesn’t exist in your reality and also not in mine. So I think I’ve answered my question for myself. It really doesn’t even matter if there are more earthquakes, it also doesn’t matter if the weather is worse than usual, neither does it really matter about that kid who made my sneakers in China. What’s important is the people around you who need help, how can we make them think for themselves so they also can think up useless things and be part of fun discussions like this one.

    Reply
  21. Adam

    The two +8’s off N.Sumatra followed in less than 24 hours by three in the 6-7 range. That’s gonna skew the graphs somewhat isn’t it. Surely.

    Unprecedented EQ action over the past 24 hours. Even I being quite the skeptic and going into my kitchen shortly to fabricate myself a tin foil hat just in case. :)

    Reply
  22. ANO

    anyone wanna look at the numbers again…. i think it would be a good idea…. jus sayin…. how about an update.

    Reply
  23. Colin

    Another update would be cool please! I know it was a long time ago but hey, I also know there’s been a few more earthquakes since.

    Reply

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