by Morgan Page, USGS, 03/14/2025
If you live in the Los Angeles area, you’ve probably felt a few more earthquakes in the past couple of years than you are used to. You’re not imagining things – there has been an uptick of felt earthquakes in recent years.
The map below shows the change. Between March 2021 and March 2023, there were only three magnitude (M) 4 or larger earthquakes in the greater Los Angeles region (shown with the gray box). In the last two years (since March 2023), however, there have been 12!
Why is this happening? Part of the reason is that earthquakes tend to cluster up in space and time. After a large earthquake, there are aftershocks that can continue for months or years. Even with smaller earthquakes, the occurrence of one earthquake makes additional quakes more likely. Take for example, the cluster of earthquakes recently near Malibu. These earthquakes are related. The magnitude 4 earthquakes in 2024 have gone on to trigger last week’s M4.1 earthquake, as well as smaller aftershocks.
Another way to view the change we’re seeing in the region is by plotting the total number of earthquakes, cumulatively, since the year 2000 (see left plot below). Here where the blue line is steep that means there have been a lot of earthquakes in a short amount of time. If you look in the plot below on the left, you can see the recent increase in the last few years. We can also plot the number of earthquakes that aren’t aftershocks of others (see right plot below). This is a way of removing the “clustering” effect discussed above. When we do this, the recent increase in earthquakes is still visible, but it’s not as dramatic. In fact, it’s similar to other changes we’ve seen in the last 20 years.
The frequency of earthquakes constantly changes, and we especially take notice when earthquakes occur in populated areas. Over the past 25 years, we’ve had, on average, about 50 M4 or greater earthquakes in California per year. However, in any given year, the number of M4 or greater quakes has ranged from 13 to 158! If we exclude aftershocks, there is still variability, but it is much less: the number of M4 or greater earthquakes not triggered by other earthquakes has ranged from 12 to 29 per year.
So yes, it’s not your imagination, you have been feeling more earthquakes in the Los Angeles area recently. These earthquakes are a reminder that we live in earthquake country. If you feel strong shaking, your best bet is to drop, cover, and hold on.
