For now the earthquakes appear to be localized.
But for California, one big question is whether these earthquakes occurring in the Mojave Desert
will have any consequences for a potentially more catastrophic rupture of the San Andreas fault,
the giant crack in the earth that runs along almost the entire length of the state near heavily populated areas.
Seismologists say there is a remote connection between the system of faults that caused this week’s earthquakes and the San Andreas.
The faults near Ridgecrest come close to a fault known as the Garlock, which ultimately intersects the San Andreas.
Dr. Heaton said it would be “pretty far-fetched” that an earthquake on the San Andreas would be triggered along this route.
But, he noted, seismologists are constantly surprised.
The current sequence of earthquakes could potentially last for years.
In the 1970s, seismologists were surprised that an earthquake near Bishop, Calif.,
began a sequence of temblors around Mammoth Lakes that eventually spread over a diameter of more than 50 miles
and included a half-dozen earthquakes of more than 6.0 magnitude.
That sequence lasted around a decade.
When a significant earthquake is followed by a related and larger one —as has happened in California in recent days —
seismologists refer to the first event as a foreshock.
A foreshock and a main quake usually occur within days or weeks of each other,
but occasionally in analyzing seismic activity in a region,
scientists will identify foreshocks that occurred months or even years before a major quake.
Some notable earthquakes have been preceded by foreshocks,
including the largest quake ever recorded, a 9.5-magnitude event that struck Chile in 1960.
A 7.9-magnitude quake had occurred in the same area the day before.
The 2011 Tohoku earthquake in Japan, which led to the Fukushima nuclear disaster, was preceded by a foreshock as well.
The 6.4 Ridgecrest foreshock on Thursday was followed by seven quakes of magnitude 4.5 or higher until the 7.1-magnitude one on Friday.
And the Friday quake so far has been followed by 15 of 4.5 magnitude or higher.
The largest known earthquake in the area occurred in 1872 and was a magnitude 8, one of the largest in California.