"A week of unusual high earthquake activity"

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Mexico, Turkey, California: Over the past seven days, from June 22nd to June 28th 2020, the world has seen a couple of big and damaging earthquakes. The Mw7.4 quake in Mexico, which was the largest quake on the American continent since January, caused 10 casualties and damaged more than 10.000 houses. Less significant damage was caused by two M~5.5 quakes in Turkey, two people were injured in a 5.8 quake in Japan.
These events, combined with an elevated frequence of posts that were shared by us on Facebook, lead to several comments wondering why we had so many quakes lately. “A week of unusual high earthquake activity” or “Many earthquakes lately” was said by different people. More comments with the same meaning can be found in earthquake groups in Facebook.

List: Most recent earthquakes in the world


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But the question is: Do we really have days of unusual high earthquake activity?

Let’s have a look on the earthquake catalog from the United States Geological Survey (USGS).
Why USGS: Because they usually detect more quakes than other agencies (e.g. Geofon) and they have a lower number of falsely reported events (like EMSC in the past couple of months….).
For the week between June 22 and 28 UTC the USGS recorded:

1 quake about M7
2 quakes about M6
27 quakes about M5 and
158 quakes about M4*

Which might look like a rather active week for many people is actually nothing unusual. If we compare these numbers with the statistics from the previous years (you can see a comprehensive statistic on Wikipedia), we see that these numbers are actually below the long-term average.
Since 2010, following average weekly earthquake numbers were recorded:

0,26 quakes about M7
3 quakes about M6
32 quakes about M5
210 quakes about M4*


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(* Improved monitoring over the past decades allowed that more smaller quakes could be recorded in recent years compared to prior years. But still the catalogs are not complete, more improvement is needed.)

Therefore, what seemed to be an unusual active week was actually a quite inactive week, slightly below the long-term average.

However, the long-term average is only useful for statistics. Terms like “normal” or “unusual” should not be used to describe the earthquake number. As global earthquake activity is not following a strict schedule, quakes occur in an irregular pattern: We have weeks (or days, months, years) with more than average quakes and also weeks, etc. with less than average quakes. Normal is only that we have earthquakes, no matter how many of them. A week with 20 strong quakes is as “normal” as a week without strong quake (because the conditions on Earth allow this kind of clustering). As “normal” as the past week.

Just because you haven’t seen earthquakes occurring in a specific way yet, it doesn’t mean that this is strange. It only means that you haven’t noticed this happening before.

Read also: Can earthquakes be censored?

Any questions about earthquake, seismology, volcanism or geology? Ask an expert!

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