San Andreas Fault: The End Is Nigh
The Southern San Andreas Fault
The last major earthquakes produced by the San Andreas fault were in 1857 and 1906. Over the last 1,400 to 1,500 years major earthquakes have occurred every 150 years on average along the southern San Andreas fault. Southern California in general experiences a major earthquake every 110 to 140 years. Since the San Francisco Bay area suffered a major earthquake in 1906 the chances of a major earthquake in this area is low.
An area of concern, though, is the southern portion of the San Andreas fault. Since the last major earthquake there was a magnitude 7.9 that struck Fort Tejon in 1857, this section of the fault is overdue. Further to the south is the section near Palm Springs which hasn't ruptured in over 300 years. According to the director of the Southern California Earthquake Center, Thomas Jordan, “eventually the fault will have to break."
The USGS estimates a 7% probability of a magnitude 8 earthquake sometime over the next 30 years. There is also a 75% chance that a magnitude 7.0 will strike within the next 30 years as well. An expert study performed by the USGS estimates that a magnitude 7.8 earthquake would cause 1,800 fatalities, 50,000 injuries, and $200 billion in damages. Geologists have calculated that there is a 99.7% probability that an earthquake measuring at least 6.7 magnitude on the Richter Scale will strike the Los Angeles area by the year 2038. The highest magnitude that experts calculate might strike is a magnitude 8.3.
Once the inevitable “big one” strikes the aftershocks could last for weeks, months, or even years. After the 7.0 earthquake struck Haiti in 2012 the country was further rocked by 52 aftershocks measuring at least 4.5 on the Richter Scale in just 12 days after the main earthquake.
Earthquake Probability Map
Los Angeles In Peril
Surprisingly the earthquake itself may be the least to worry about for Los Angeles. The USGS report estimates half of the fatalities will occur from fires following the earthquake in what may very well be a repeat of the 1906 San Francisco earthquake. The report predicts that numerous small fires resulting from the earthquake will grow into massive uncontrolled fires due to ruptured waterlines and blocked roadways, which will hinder rescue personnel from responding and result in large portions of Los Angeles being destroyed. If the earthquake occurs during Santa Ana winds the devastation from uncontrolled fires would be even more catastrophic.
The earthquake will cause most infrastructure to collapse. Roadways will either be blocked or destroyed, and lines that supply Los Angeles with electricity, water, and gas that run across the San Andreas fault will be ruptured. Experts estimate that repairing these essential lines will take months. The situation would be exacerbated by extremely low water levels throughout the reservoirs in southern California. If the water lines can't be restored quickly, Los Angeles will run out of water within six months. Some of the infrastructure could take up to a year to repair.
Experts predict the next big quake will be 60 times stronger than the 1994 Northridge earthquake. Recent research has discovered a 125-mile stretch along the fault where large sections are sinking and others are rising indicating a massive buildup of pressure and energy. Eventually the fault will slip and re-level these areas. There has been 26 feet of movement in the tectonic plates since the last big earthquake in 1857: that's 26 feet of unreleased energy building up within the fault.
Seismic Hazard Map
California has dozens of faults that intersect across the entire state making up multiple active fault zones, San Andreas is only one of these faults. There is the distinct possibility that a major earthquake along one of the faults in California could trigger other faults to rupture as well, spreading destruction across a large swath of southern California. When multiple faults rupture, the resulting earthquake is more powerful and much more damaging than anything the faults could produce alone.
The possibility of a multi-fault rupture goes beyond speculation; there is a historical precedence for the phenomenon. During the 1992 Landers earthquake, multiple faults ruptured, producing a magnitude 7.3 earthquake. Another powerful quake that hit southern California occurred in 1812; this estimated 7.5 magnitude earthquake was likely the result of a rupture along the San Jacinto fault that triggered a rupture along the nearby San Andreas fault.
Scientists studying a repeating series of micro-earthquakes near Parkfield, California, found that the 1992 Landers earthquake triggered a series of magnitude 4 earthquakes. Next the team found a change in the fault that was caused by the 2004 Sumatra mega-quake. This evidence is proof that powerful earthquakes can weaken faults all around the world. They now believe the San Andreas was pushed further to the brink of rupture by the 2004 Sumatra earthquake. In 2005 and 2006 there was an above-average number of powerful magnitude 8 earthquakes around the world. This series of quakes is strongly believed to have been triggered by the 2004 Sumatra earthquake.
Another earthquake of magnitude 8.6 centered off of Sumatra in April 2012 sent seismic waves traveling through the earth triggering earthquakes around the world. Over the following week numerous faults across the globe which had been weakened by the powerful 8.6 tremor began to rupture. The 8.6 earthquake is the largest ever recorded for a strike-slip fault; the most powerful earthquakes tend to be caused by subduction faults. The reason for the unprecedented strength was that it wasn't just one fault that slipped, but at least 3 or 4 faults that intersected each other and ruptured in sequence, creating a much more powerful earthquake. There is the potential that current estimates of future earthquakes in southern California are underestimates. With so many faults in one area and several close to failure, there should be concern that a powerful earthquake in one fault is likely to trigger ruptures in many of the surrounding and intersecting faults. The danger goes far beyond California, as a major earthquake, particularly a multi-fault rupture, has a substantial probability of triggering earthquakes across the globe.
Ring of Fire
Era Of The Mega-Quake
Starting in 2004, a series of mega-quakes began striking the notorious Ring of Fire. A magnitude 9.1 hit Sumatra in 2004 hailing in the new era of mega-quakes. Then beginning in February 2011 a series of four mega-quakes struck within 13 months of each other. An 8.8 magnitude tremor hit Chile in 2011; New Zealand suffered three earthquakes including a 7.1 and two separate 6.3 magnitude earthquakes which occurred in 2010 and 2011, next was Japan, where in 2011 a mega-thrust earthquake measuring 9.0 on the Richter Scale killed thousands.
Scientists are beginning to speculate whether there was a connection between these mega-tremors. If there is a connection, and if one wanted to speculate about where the next mega-quake might hit, the remaining hot-spots along the ring-of-fire that have yet to be hit include the faults along the Aleutian Islands, the Cascadia Subduction Zone near Washington state, and the San Andreas fault along with all of its sister faults.
Even more frightening is the fact that at least two out of five nuclear power plants in California were not built to withstand earthquakes of the magnitude that experts believe may be imminent. The plant at San Onofre was only built to withstand quakes of 7.0 magnitude, and the plant at Diablo Canyon was built to withstand a quake of 7.5 magnitude. With both of these plants designed to withstand events smaller than historical and predicted earthquakes, the possibility of a nuclear disaster is a valid concern. The prevailing winds would spread radioactive debris across much of America.
Frequency of Occurrence of Earthquakes
8.0 and Higher
Groundwater Extraction Causes Earthquakes
Recent studies including evidence from multiple GPS stations indicate that the removal and depletion of water in the large underground aquifers is altering the movement along the San Andreas fault. This change could lead to more earthquakes or could help induce a much larger earthquake. This problem will only worsen as more and more water is removed from the aquifer due to extended droughts and the need to irrigate thousands of acres of farmland. There is a historical precedent for this phenomenon as well; in 2011 Spain was hit by a 5.1 magnitude earthquake that was caused by groundwater extraction.
How concerned are you about a major earthquake in southern California?
© 2016 Lloyd Busch