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Is the seismic activity of the Earth increasing, or are we getting to hear more frequently about earthquakes just because seismographs are more widely available now and it is easier for news to disseminate widely?


Certainly, there is a lot of perceptual bias in these types of questions, i.e. it is easy to ‘see’ an increase when there are earthquakes in areas that get reported on as opposed to when earthquakes occur in areas without many reasons to report. Additionally, there has been a real increase in the number of seismometers through time and as such a true increase in the number of earthquakes recorded independent of any true change in rates.

The more detailed, scientific answer (1) is complex and (2) depends on what aspects of earthquakes you are considering. In short, if looking at numbers of earthquakes, there have been short term increases in rates of large magnitude earthquakes, but these are not beyond what you would expect for a random process, e.g. Shearer & Stark, 2012.

Similar results are found for moderate magnitude earthquakes, e.g. Parsons & Geist, 2014. However, there is some evidence that if you look at the rates of seismic moment release as opposed to a number of earthquakes, there may be more variability in rates than is expected by random processes, e.g. Zaliapin & Kreemer, 2017, i.e. the potential for real changes in the rate of seismic moment release, and in this particular case, an increase.

When thinking about these types of results, this commentary by Beroza written in relation to the Shearer & Stark paper is instructive. It highlights that finding time dependence/variation in rates in seismic catalogs is pretty hard (especially when you consider that you need to filter out known time-dependent processes, i.e. aftershocks, but this in itself if challenging) and that ultimately we are operating with an extremely limited set of observations in terms of how long we’ve been accurately recording earthquakes.

Simply put, with very short time periods of observation for a process that operates on very long time scales, like earthquakes, it is really hard to say with certainty that rates are increasing, decreasing, or effectively the same within the range of variation expected with a random process.