A series of small earthquakes up to magnitude 4 started popping off right next to the San Andreas fault at the end of September, giving Californian seismologists the jitters.

This swarm of more than 200 mini-quakes radiated from faults under the Salton Sea, right down at the southern end of the San Andreas fault.

And although the small quakes only released tiny amounts of energy, the fear was that this fidgeting could be enough to trigger an earthquake on the big fault.

“Any time there is significant seismic activity in the vicinity of the San Andreas fault, we seismologists get nervous,” said Thomas Jordan, director of the Southern California Earthquake Centre in Los Angeles. Because despite …