Reply by Dr Roger Musson, Head of Seismic Hazards at the British Geological Survey
This question is founded on a commonly-encountered false premise, namely that earthquakes are on the increase. Long-term records show that the number of earthquakes occurring world-wide is broadly stable, with no more clustering than would be expected from a more or less random process. Of course, the number of earthquakes recorded per year has increased, as more recording stations are set up, but the increase in recorded small earthquakes is not the reason for this misperception that earthquakes are increasing. There are two main reasons. The first is that most people other than professional seismologists learn about earthquakes through the media, and the media are mainly interested in earthquakes that have a human impact. Large earthquakes in remote parts of the oceans don't get reported by TV or newspapers, and most people have no idea how common they are. When, by chance, a few earthquakes happen to strike populated areas within a short space of time (as in the case of Haiti - Chile - Turkey in 2010), it creates a false impression of more earthquakes than normal. The classic case of this was 1976, when there was a succession of high-fatality events hitting the newspapers. But in fact, the total earthquake energy released that year was substantially LESS than average. The key fact was where earthquakes occurred, not how many there were.
The second reason is that people have short memories. Who, other than a seismologist, actually remembers how many earthquakes there were in 1976? Or the period 1950-1964, which saw a cluster of truly great earthquakes? So the impression of an increase in earthquakes is founded on a lack of adequate comparison.
As to the issue of nuclear blasts, of course, nuclear tests are now extremely uncommon, if they happen at all. Nuclear tests certainly can induce minor seismicity in the area around the test site. In the heyday of Cold War nuclear tests, one of the main Soviet test sites was in Novaya Zemla, an area of virtually no natural seismicity. Even though nuclear tests have long since ceased there, there is still the occasional earthquake as the legacy of the testing period. But the forces that drive the movement of the planet's tectonic plates, and thus earthquakes, operate at depths of 30 km and deeper, and are vastly larger than anything mankind can produce through nuclear explosions.