# Has there been an increase in earthquake activity?

*Cross posted from my personal blog: Have there really been more earthquakes than average?*

*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. 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.

Let’s take earthquakes based in the M6.0 – M6.9 range. Why am I picking earthquakes in the magnitude 6 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.

PDE-Q 2010 01 02 084532.05 12.42 141.96 2 6.1

PDE-Q 2010 01 03 214805.32 -8.74 157.48 26 6.6

PDE-Q 2010 01 05 045538.91 -58.17 -14.70 10 6.8

PDE-Q 2010 01 05 121532.21 -9.02 157.55 15 6.8

PDE-Q 2010 01 05 131142.82 -9.05 157.89 35 6.0

PDE-Q 2010 01 09 055130.47 -9.13 157.63 12 6.2

PDE-Q 2010 01 10 002739.32 40.65 -124.69 29 6.5

PDE-Q 2010 01 12 220041.49 18.39 -72.78 10 6.0

PDE-Q 2010 01 17 120001.08 -57.66 -65.88 5 6.3

PDE-Q 2010 02 01 222816.92 -6.11 154.46 32 6.2

PDE-Q 2010 02 05 065905.64 -47.90 99.66 1 6.2

PDE-Q 2010 02 06 044458.40 46.84 152.73 30 6.0

PDE-Q 2010 02 07 061000.24 23.48 123.64 21 6.3

PDE-Q 2010 02 09 010344.44 -15.05 -173.49 10 6.0

PDE-Q 2010 02 13 023428.69 -21.89 -174.77 11 6.1

PDE-Q 2010 02 15 215148.56 -7.19 128.78 130 6.2

PDE-Q 2010 02 18 011319.93 42.61 130.70 580 6.9

PDE-Q 2010 02 22 070054.60 -23.72 -175.98 35 6.0

PDE-Q 2010 02 27 065234.57 -34.80 -72.65 35 6.2

PDE-Q 2010 02 27 071228.81 -33.83 -71.91 35 6.0

PDE-Q 2010 02 27 073718.52 -36.84 -72.54 35 6.0

PDE-Q 2010 02 27 080123.93 -37.71 -75.21 37 6.9

PDE-Q 2010 02 27 082529.61 -34.76 -72.37 35 6.1

PDE-Q 2010 02 27 154541.09 -24.59 -65.43 38 6.3

PDE-Q 2010 02 27 190008.01 -33.42 -71.91 34 6.3

That works out to roughly one earthquake in the magnitude 6.0 range every 2.4 days. That doesn’t seem unreasonable, 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.

2010 25 2.4

2009 142 2.57

2008 168 2.18

2007 178 2.05

2006 142 2.57

2005 140 2.61

2004 141 2.60

2003 140 2.61

2002 127 2.9

2001 121 3.02

2000 146 2.51

1999 116 3.15

1998 109 3.35

1997 120 3.04

1996 149 2.46

1995 183 1.99

1994 146 2.5

1993 137 2.66

1992 166 2.20

1991 108 3.38

1990 109 3.35

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.

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.

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! Simply put, there is absolutely *nothing strange happening.*

In fact, thanks to this normal curve you can basically predict, with a 99.7% chance of success, that an earthquake of equal / greater than M6.0 will occur somewhere around the world within the next 3.5 days.

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.

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!

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