It’s already mid-March, but I still wanted to do a quick yearly earthquake update, which has become a bit of a tradition by now at the beginning of each new year.
The graph below shows the yearly count of M5+ earthquakes since 1970, updated to include 2021. As the graph shows, last year was the fourth highest count of M5+ earthquakes (2206 in total) over the past 52 years (after 2007, 2010, and 2011).
One of the main explanations for this unusually high number is that there were three M8+ earthquakes in 2021, which is very rare. Each earthquake generates many aftershocks, and the stronger an earthquake is, the more aftershocks it creates. An M8+ earthquake will easily generate hundreds, if not thousands, of aftershocks. And this most likely will also include several dozens, if not a few hundred, of M5+ aftershocks.
The next graph shows a histogram of the number of yearly M8+ earthquakes since 1970. About 80% of the past 52 years (42 out of 52) had no or only one M8+ earthquake. There were eight years that saw two M8+ earthquakes. Only one year (2021) had three M8+ earthquakes, and one year (2007) had four of them.
Clearly, having three or four M8+ earthquakes is very rare, and the two years in which this occurred (2007 and 2021) indeed also had two of the four highest M5+ earthquake counts, due to the many strong aftershocks these multiple M8+ earthquakes caused. So, no real reason for concern, but we’ll keep an eye on it! And if you want to do so as well, I’ve collected some useful earthquake maps and charts, which are continuously updated, into one convenient place.