Northern California suffered an “Earthquake Storm” on Sunday, as 60 smaller aftershocks rolled through Northern California following the magnitude 6.0 on the Richter Scale earthquake that struck Sunday at 3:20 a.m. 

Sunday’s earthquake is the 4th serious quake this year after a period of low activity. Charles Richter, the seismologist who designed the measure of earthquake intensity in 1935 at the California Institute of Technology, warned that when there are a lot of earthquakes, the risk of bigger earthquakes increases.

The series of quakes that hit since Sunday ranged in size from magnitude 0.6 to 3.6 on the Richter magnitude scale and were centered primarily in American Canyon, the Geysers, and Napa. The U.S. Geological Service warned there is still a 50-50 chance of a magnitude 5.0 or larger earthquake hitting in the next five days.

After two decades of mild and intermittent earthquake activity, California has suffered four serious magnitude quakes this year. The state was hit with the 6.8 magnitude Cape Mendacino quake on March 9th; the 4.4 magnitude Westwood quake on March 17th; the 5.1 magnitude La Habra quake on March 28th; and now the 6.0 South Napa quake.

Geophysicist John Dvorak, author of the book “Is California Overdue for a Big Earthquake?” warned that the mild 4.4 earthquake that rattled Los Angeles at 6:30 A.M. in the morning on March 17th could be the first in a series of increasingly higher intensity earthquakes that could build over an extended period in California. He cautioned, “A lengthy vacation from earthquakes certainly sounds nice”, but a quake break can just be the calm before the earthquake storm. He offered his thoughts in a March 28th interview with the Christian Science Monitor:

Q: Scientists weren’t just wrong about earthquakes in the centuries leading up to the 1906 San Francisco quake. They were really wrong. What did they believe?
 
A: If you go back to the Enlightenment, they thought they were related to chemical explosions. By the 19th century, many scientists said they were caused by large volcanic explosions happening within the Earth. There was no wide acceptance of the idea that earthquakes were actually caused by the sliding of great crustal blocks against each other until the 1906 earthquake, which ruptured the earth’s surface for almost 300 miles. The ground had actually slid tens of feet along that rupture.
 
Q: What is an “earthquake storm”?
 
A: During the last few decades, it has been realized that earthquakes do not occur randomly, nor do they occur like clockwork. Instead, earthquakes, even large ones, tend to cluster in time and space. An earthquake storm is when there is a cluster of large earthquakes in a region [which] occur over a period of several decades. The best examples are the earthquakes that are now happening in northern Turkey along the North Anatolian fault. The storm began in 1939. Since then there have been 13 major earthquakes, and scientists expect at least one more major earthquake is yet to happen at the west end near Istanbul. So the Turkish government is trying to retrofit many buildings for the coming shaking as well as protect many of the art treasures in the city and much of the ancient architecture.

Q: How does California fit into the world of earthquake storms?

A: Most of the motion between the Pacific and North American plates occurs along coastal California. In the last hundred years, there has been only one significant earthquake along those plates: the 1989 Loma Prieta earthquake, also known as the World Series earthquake. But during the previous hundred years before that, there were five significant earthquakes along the California coast, in 1812, 1838, 1857, 1868, and 1906. Large earthquakes are the major means by which seismic energy gets released after building up between the two tectonic plates. And so, one or more large earthquakes are in California’s future, it is a matter of when?

Yesterday’s “South Napa Earthquake” did not cause any fatalities. About 172 patients were treated for injuries, and 13 people were admitted to the Queen of the Valley Medical Center in Napa. The injuries roughly split between orthopedic injuries to hips and ankles, and those with medical issues like respiratory and heart problems, according to hospital President Walt Mickens. About another two dozen people were treated in the Vallejo area for cuts, bumps, and bruises.

The string of earthquakes this year so far have not caused any deaths or huge property losses, but when California starts getting a series of earthquake storms, it usually means that people need to prepare for a very big earthquake in the near future. The last time an earthquake hit the Bay Area was in 1989, when the Loma Prieta quake at magnitude 6.9 caused billions of dollars in damage and was responsible for 63 deaths and 3,757 injuries in the affected areas. Very few people understand that California “earthquake vacations” usually mean that pressure underground is building. 

To read more about how California is focused on fighting global warning rather than preparing for big earthquakes, click on California Utility Customers Must Pay $331.8 million for CO2 Auction.