Earthquakes

Magnitude 5+ Earthquakes - Global

5.5 Earthquake hits Vanuatu.

5.3 Earthquake hits the Izu Islands off Japan.

5.1 Earthquake hits Fiji.

5.0 Earthquake hits the Hindu Kush, Afghanistan.

New Theory on Major Earthquakes

A widely accepted theory about earthquakes has received a shakeup.

A team of geologists studying the San Andreas fault near Los Angeles found that bigger earthquakes aren't necessarily preceded by longer periods of inactivity on the fault. The going wisdom about earthquakes is that the longer a fault goes without a major earthquake, the bigger the quake will be when it finally strikes. The theory seems particularly apt for the San Andreas fault, which marks the boundary between two tectonic plates. As the Pacific plate moves northward relative to North America at about 4.5 cm per year, friction stops the fault from slipping. The longer that strain jacks up, the farther the plates will jolt when they finally let go and the larger the resulting earthquake will be. Or so the thinking went.

But a group found that the theory doesn't hold up for the segment of the fault near the southern California town of Wrightwood.

The team's analysis provided the most complete long-term record of activity for any fault in the world. And it contradicts the conventional wisdom: Shorter quiet periods of less than a century were generally followed by larger earthquakes, and longer periods of several hundred years preceded smaller quakes. Although this appears counterintuitive, the larger pattern is more logical. It appears that strain is not released entirely with each earthquake but continues to accumulate through four or five or more earthquake cycles. Finally, the strain is released by one big quake or a cluster of smaller shocks.

The authors caution that they don't know yet if the activity at the Wrightwood fault segment is typical of the entire San Andreas fault or of faults in general. But if it is, the research could change the way scientists estimate the probability of earthquakes.