Is the Napa Quake a Precursor to the Big One?

Was the 6.0-magnitude earthquake that recently struck Northern California an isolated seismic event, or the harbinger of a worse quake to come?

Jittery Californians and earthquake-watchers are asking themselves that question after Sunday's quake on the Hayward-Rodgers Creek Fault — the area’s largest in 25 years — struck the Napa Valley. The San Andreas Fault, a continental transform fault that runs some 810 miles through California, is overdue for an epic seismic event of near 8.0 magnitude. Such a quake is expected to create a national disaster and produce devastation to areas within 50-100 miles from the quake zone. The potential loss of life could be great if the “Big One” struck urban areas near the fault, such as San Francisco, Los Angeles or Palm Springs.

Despite the concerns, nobody really knows when a 7.0-8.0 magnitude is due as seismologists cannot predict the timing of earthquakes with any precision. However, there may be more cause for concern on the southern part of the fault than in the northern section.

According to the U.S. Geological Survey, catastrophic earthquakes strike along the northern, central, and southern sections of San Andreas every 150 years or so, citing the past history in the region spanning 1,400 years. The last epic shocks along the fault were on the central and northern areas of the fault, the 1857 and 1906 events. The 1857 quake, known as the Fort Tejon earthquake, had a magnitude of 7.9, and earthquake zone reached well into southern California. However, the epicenter of the quake was 85 miles north of Los Angeles. The 1906 earthquake, which had an epicenter in the northern fault area in the Bay Area, is estimated to have produced a magnitude of 7.8.

Thus, scientists say that Southern California may be overdue for another colossal temblor, but San Francisco is not as likely to see one soon, as only about a century has passed since its last epic quake. This is not to say that more damaging quakes are not possible for the San Francisco area. Quakes between 6.0 and 7.0 in magnitude can strike at any time, say seismologists.

One of those quakes happened in 1989. The Loma Prieta Earthquake, often dubbed “The World Series Quake” because it occured during the pre-game broadcast of Game 3 of the baseball championship between the San Francisco Giants and Oakland A’s. A magnitude 6.9 on the Richter scale, it caused 69 deaths, nearly 4,000 injuries, and more than $6 billion in property damage.

Southern California had a 6.7 magnitude quake in 1994 called the Northridge Earthquake. The original quake and its many aftershocks killed 57 people and caused $42 billion in property and infrastructure damage.

But despite their focus on the southern section of the fault, the “Big One” can possibly run far along the San Andreas, according to seismologists, creating damage spanning hundreds of miles.

Research conducted by the University of California eight years ago concluded that the fault is currently at sufficient stress level for the “Big One” to happen. The study also concluded that the risk of a large earthquake may be increasing more rapidly than researchers had previously thought. The study points to the more southern areas of the fault. It says that while the 1857 and 1906 quakes originated from the central and northern sections of the fault, the southern area of the fault hasn’t seen an equivalent rupture in more than 300 years.

“The information available suggests that the fault is ready for the next big earthquake but exactly when the triggering will happen and when the earthquake will occur we cannot tell,” said Yuri Fialko, a professor of geophysics at UC San Diego. “It could be tomorrow or it could be 10 years or more from now.”

While predicting the timing of the next "Big One" may elude scientists, they are somewhat certain about the odds. The Uniform California Earthquake Rupture Forecast, prepared by a working group of seismologists and geophysicists, predicts the probability of such epic earthquakes. It estimates that the northern section of the San Andreas Fault only has a 21% of a 6.7 or greater magnitude quake in the next 30 years, while the southern part of the fault has a 59% risk. 

An event at that size and originating from the southern section of the San Andreas Fault could possibly result in hefty damage to urban areas such as Palm Springs, San Bernardino, and the Calexico/Mexicali border area. Such a quake would have notable effects much of Southern California, including Los Angeles, Orange County, and San Diego. The region has a population of about 23 million people.
While a quake of that size could make the ground quiver like a Jell-O mold that’s been dropped, steps have already been taken to brace infrastructure. But some 1,500 concrete buildings, including hotels, churches, and nursing homes have not yet been retrofitted. Experts estimate that about 5% of these would collapse during a large earthquake, although they cannot predict which ones.

Some scientists worry that hydraulic fracturing activities in California may hasten the possibility of major earthquakes. They say that pumping water underground already leads to dangerous earthquakes in regions that had not been prone to tremors in the past. They claim that earthquake risks should be factored into decisions about where to place drilling rigs where water is pumped underground.

The water injection involved in hydrofracking appears to prime cracks in the rock, making them vulnerable to triggering by tremors from earthquakes thousands of miles away. Nicholas van der Elst, a post doctorate research fellow at Columbia University's Lamont-Doherty Earth Observatory is worried that underground injection of water may hasten or exacerbate seismic activity. As the lead author of one of a trio of studies published earlier this year in the journal Science, van der Elst said: "These fluids are driving faults to their tipping point."

Back in March, a 4.4-magnitude quake rattled Los Angeles. A few weeks later a 5.1 magnitude earthquake occured at the nearby Puente Hills fault, a lesser known but potentially deadly fault. The Puente Hills fault runs through northern Orange County and underneath parts of Los Angeles. Experts now believe that the Puente Hills fault may pose a greater threat to Los Angeles the San Andreas. 

And while nobody is pointing the finger directly at fracking operations, Kyle Ferrar of the FracTracker Alliance was quick to note that the first quake's epicenter was only some 8 miles from an active wastewater injection well. The possible correlation has the Los Angeles City Council worried as well

In Orange County, some residents are asking whether the second quake, known as the La Habra Earthquake had anything to do with fracking operations near its epicenter. They not that while earthquakes are far from a rarity in their area, many residents believe that it's not unreasonable to declare a moritorium on fracking in town such as Fullerton until they a determine whether or not there is a connection. 

In other areas in the U.S. where fracking takes place, injection wells have been shown to create seismic activity by affecting faults at as far away as 7.5 miles. Geologists working for the State of Ohio have confirmed a direct link between hydraulic fracturing and a recent spate of seismic activity in region. The scientists' findings have prompted the state to issue new permit conditions for fracking that are among the nation's strictest. 

Ohio has been investigating recent tremors near Youngstown, in the northwestern part of the state. The geologists found that the high-pressure injection of water and fracking compounds into the underground rock formation known as the Utica Shale have likely stressed a previously unknown fault. 

Hydraulic fracturing and the related practice of pumping dirty waste fluids deep underground have also been cited as the cause of unprecedented swarms of earthquakes in Arkansas, Oklahoma, and Texas. A recent study by the U.S.. Geological Survey found that the rate of earthquakes of more than 3.0 has increasing greatly in those areas since 2001, at the beginning of the shale drilling boom. 

"While the seismicity rate changes described here are almost certainly manmade, it remains to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production," said the study. 


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