(NaturalNews) For Los Angeles, California, May 2014 was a month of heightened seismic activity, boasting five earthquakes that measured greater than 4.0 on the Richter scale. The sudden increase in seismic activity on the West Coast hasn't been witnessed since 1994 -- the year that 53 quakes rumbled through the area -- the year of the deadly Northridge earthquake.
Scientists can only speculate why the earth is beginning to shuffle along the Santa Monica Mountains.
Is the recent spike in seismic activity a sign of more trembles to come? Are they part of a new sequence of tremors leading to a larger, more deadly quake? Are they a mere aftershock of the 1994 Northridge quake? Are they caused by the uptick in hydraulic fracturing going on in the region?
Ever since 1994, entire calendar years have passed by without bringing any quakes over 4.0. The recent unexpected flux has baffled scientists who are unsure whether another large quake is on the horizon.
"Probably this will be it, and there won't be any more 4s. But the chance we will have a bigger earthquake this year is more than if we hadn't had this cluster," U.S. Geological Survey seismologist Lucy Jones said. "Every earthquake makes another earthquake more likely."
So far in 2014, Los Angeles has shouldered mild quakes that have exceeded the 4.0 mark. These were felt over wide swaths of land in the Fontana and Rowland Heights districts but did not cause severe damage. The largest quake so far was measured in La Habra at 5.1; it tore up property that caused several millions of dollars in damage.
The most concerning seismic activity is along the Santa Monica Mountains. Just along the 405 Freeway, a fault line is beginning to produce concentrated and repeated seismic activity. Fifteen smaller quakes occurred along this fault line throughout the winter of 2014. Recently, the quakes along this line have increased in size. On March 17, a 4.4 struck Encino, and in May a 4.2 hit nearby Brentwood.
Caltech seismologist Egill Hauksson says that the Santa Monica Mountains were formed by earthquake activity over a million-year period, and new waves of seismic activity may indicate that the process is beginning again.
The quakes, near Wilacre Park, are all within less than three miles of each other.
Suspicious, Hauksson said, "We don't know if it [Northridge] has ended or if it will keep going."
What Hauksson means is that seismologists studying the Santa Monica fault are unsure whether the new string of quakes is connected to the 1994 Northridge earthquake that killed 57 people. Some of his colleagues believe that the recent spike in seismic activity could be an aftershock from the Northridge quake that occurred 20 years ago. Hauksson, on the other hand, believes that the recent seismic activity is part of a new seismic sequence.
Scientists wonder if hydraulic fracturing in the region is causing the quakes
They have also been looking much more closely at the La Habra quake, since its epicenter lies in a region that has been fracked for decades.
After reviewing the 5.1 quake as well as the 4.1 aftershock in Rowland Heights, Hauksson and colleagues reasoned that hydraulic fracturing is probably not the cause of the quakes. They report that petroleum extraction from Santa Fe Springs a year prior to the quake was too far away from the quake's epicenter to make a difference. The oil drilling was roughly seven miles from the quake's epicenter, so the connection was ruled out.
There was also "no trail of seismicity from the oil field to the 5.1 earthquake," Hauksson said.
The U.S. Geological Survey paints a much different picture, showing how increasing hydraulic fracking in the eastern U.S. can be statistically correlated with huge spikes in seismic activity. Between 1970 and 2000, an average of 20 quakes greater than 3.0 have struck the Eastern portion of the U.S. yearly. In the past four years, as hydraulic fracturing has increased, there have been about 100 quakes striking every year.
Hauksson admits that it may be impossible to make connections, since there's no publicly available data accounting for the volumes of fluid being injected into the ground. Additionally, it's difficult to know where this is occurring and how it may pressure certain layers of the earth's crust.