Are Earthquakes Increasing? March 2010 Analysis

Most Powerful Quakes Since 1990

The 8.8 quake in Chile last month was the seventh-most powerful earthquake since 1900, and the second-most powerful of the last twenty years – behind only the 9.0 quake that triggered the infamous tsunami in 2004. In January, Haiti was devastated by a 7.0 quake. There have been other reports recently of major earthquakes in Taiwan, Turkey, and off the coast of Japan – not to mention the dozens of aftershocks that continue to shake Chile. Many people are wondering if there has been an increase in earthquakes lately, and it’s a question that deserves a solid investigation.

I looked at the ANSS global earthquake catalog and analyzed their records. There have been over 30,000 earthquakes of 5.0 or greater since 1990. The earth has been having quakes of 6.0 or larger, on average, almost every other day for years. Most of them go relatively unnoticed, but sometimes several bigger ones hit populated areas around the same time, and it’s happened so far in 2010. But is it unprecedented?

First, let’s just look at the number of earthquakes recorded per year at different magnitudes (2010 is through March 10).

There are no clear trends for 5.0+ from 1990-2004, although the last five years have all had more quakes than any of the years before them. However, if you only look at 6.0+ even that trend doesn’t hold, as ’94, ’95, and ’00 all had more 6.0+ quakes than three of the last five years. (There are some slight increasing trends depending on whether you focus on the peaks or the troughs, but I suspect that we simply missed more of these smaller quakes in the past than we do now.) It is true that ’07 and ’08 are the top two in either breakdown, but ’09 declined closer to the recent average.

Let’s move on to 7.0+, which would be even harder to miss than the 6′s. Here there is no trend at all. ’08 is actually below the 20-year average of 14 per year, and ’07 comes in at a measly third place below the records from the 90′s that are still standing.

There actually is an interesting trend in the big leagues at 8.0+. I doubt it would have been easy to miss many of these, even in the 70′s when we only recorded 2. Then we had 3 in the 80′s, 7 in the 90′s, and 13 in the 00′s! It’s not very comforting to say the medium quakes aren’t increasing if the big ones are! But even here we don’t have a runaway increase. We did have a record 4 in ’07, which was almost more than the entire 70′s and 80′s combined! But the following year we had none at all, and only 1 in ’09.

If you move up even higher, to the 9.0′s, there is no pattern at all. We have, on record (though not in this catalog), two in the 50′s and two in the 60′s, and the only other one was the 2004 Tsunami. We’ve had fewer super-quakes in the last forty years than we did in the 50′s and 60′s!

So depending on how you select the data, there does seem to some increase in earthquake activity over the last few decades – although some of that may simply be due to better detection, and it all comes down to where you start the data. 5+ shows an increase, 6+ sort of does, 7+ doesn’t, 8+ does, but 9+ definitely doesn’t. Who is going to draw the line and decide whether we have been having an increase in “big” quakes or not? Yes, 2007 was a big year, but the last two years were very ordinary, and people weren’t getting too worked up then. Is there any more reason to get excited now?

Let’s look at what we have so far in 2010…

Through March 10, we have recorded 514 quakes of 5.0 or larger. That puts us on pace for about 2,718, which would beat 2007′s record of 2,293 by a large margin! We have already had 45 quakes of 6.0 or larger, which puts us on pace for about 238, crossing 200 for the first time ever. Record earthquake activity?

Not so fast. We just had a major earthquake in Chile that has triggered dozens of aftershocks, and this is affecting the average, as the earth will most likely not continue at this pace for the rest of the year! It has been 12 days since the Chile quake. For comparison, let’s look at the number of quakes in the 12 days after the 2004 Tsunami quake.

We had far more 5.0+ quakes immediately following the Tsunami quake than we did the Chile quake (after all, a logarithmic 9.0 is 58% larger than an 8.8), and the number of 6.0+ was about the same. In fact, before the Chile quake happened, we were only on pace for fairly uninteresting counts of about 1,812 and 134, respectively (and this already included the Haiti quake). To give you an even better idea of the typical volatility of these numbers, let’s look at where each year stood through March 10 compared to where they finished at the end of the year.

Nearly 19% of the way through the year, some years had only had 10% of their quakes at certain levels and some had already had over 28%. The leader of course was 2005, which began less than a week after the Tsunami and started the year with an unusually high number of powerful quakes that were mostly aftershocks.
It ended with fewer quakes than the next four years even though it holds the record for the number of quakes in the first 69 days of the year. If this year ends up like 2005, it will look fairly average, or at least “average” as far as the last decade or so is concerned. We could end up with less than 1,900 quakes of 5.0 or larger. Of course it’s also possible that we’ll have another 8.0+ before the year is up, which may trigger enough aftershocks to give us another big year.

The only real long-term trend I see that isn’t easily explained by better detection methods is the increase in quakes of 8.0+, which were nearly double in the 00′s (13) what they were in the 90′s (7). But we have not seen an increase in the far more dangerous 9.0′s, so even there it’s somewhat arbitrary. W’ve had 1 of the 8′s so far in 2010, which is nothing extraordinary. We will have to wait and see how this year plays out, as I assume the Chile aftershock effect will begin to dissipate. In conclusion, it doesn’t look like 2010 is going to set any records just yet.

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3/13 UPDATE: Data through March 11th for 5.0+ and 6.0+ shows 529 and 48 quakes year-to-date, respectively, and our pace in the wake of Chile is still increasing at, 2,758 and 250, respectively. The 13 day comparison with the Tsunami now looks like this:

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Notes: I took all data from the ANSS global earthquake catalog. I pulled up lists of quakes, copied them to a text file, read them into a C++ file that output a text file of queries which I inserted into a MySQL database. I ran SQL queries on that data to generate most of the numbers and tables given above. It is possible that I have made errors in the transferring process, and it is also possible that I have made errors in my analysis above. The ANSS catalog is constantly being updated, which may or may not include updates to recent quakes that I have already analyzed. Feel free to do your own research with the catalog, or find another source of information, and come to your own conclusion.