Megaquakes Imperil US Northwest, South and Midwest

California’s infamous San Andreas fault has long frightened and fascinated Americans. Fewer know of the Pacific Northwest’s even greater megaquake risk. Most are oblivious to a very real threat to Memphis and St. Louis.

Frequent small and medium quakes remind Californians of their peril. Awareness means better preparedness. Stricter building codes, more effective emergency services, and residents better trained to cope with catastrophe – all translate into lives saved. It helps too that the San Andreas isn’t capable of quakes as intense as the other at-risk regions.

Even so, California’s large population centers make it likely the dreaded “big one” will wreak widespread destruction and leave thousands dead.

Here’s what you need to know about the risks to those less known danger zones – and how you can prepare:

(This brief documentary explains the basics of plate techtonics. Collisions between massive plates on Earth’s crust cause earthquakes, tsunamis and volcanic eruptions.)

The Pacific Northwest: Overdue for a Massive Quake

Juan_de_fuca_plateThe Cascadia subduction zone extends over 600 miles – from Canada’s Vancouver Island to the northernmost counties of California. It lies just off the Pacific coast. The 90,000 square mile Juan De Fuca oceanic plate pushes against the lighter, weaker North American contintental plate at a rate of 40 millimeters per year. It buckles upward gradually, three to four millimeters per year, usually over centuries, until the strain is too great and the plate snaps back like a spring. It can plunge as much as several meters.

Scientists were unaware of the fault’s existence until the 1960s. They didn’t know it posed a threat until the late 1980s.

Geological evidence from the Northwest and historical documentation of related Japanese tsunamis prove a megaquake of about nine on the Richter scale devastated the Northwest on January 26, 1700. That was over a hundred years before any written historical records existed there.

(The Richter scale of earthquake magnitude – how it works.)

A rift tore open the end of the subduction zone and raced up its entire length at over two miles per second. A quake jolted the ground for four to six minutes. The land plunged over a meter. Much of that land was submerged below the ocean. So a huge column of ocean water collapsed. Half of the volume sped across the ocean, sending tsunamis to Japan just ten hours later. The other half slammed across the length of the Northwest coastline within 15 to 30 minutes after the quake subsided. The tsunami ranged in height from 20 to 100 feet, depending on the coast’s contours.

Scientists have found evidence of 41 subduction quakes in the Northwest over the past 10,000 years. They occur, on average, every 243 years. We are 73 years overdue. It might hit us tomorrow. Or it might not happen for another hundred years. Jay Patton, a doctoral student who co-authored an extensive 2012 study of the Cascadia subduction zone states bluntly. “By the year 2060, if we have not had an earthquake, we will have exceeded 85 percent of all the known intervals of earthquake recurrence in 10,000 years.”

The southern half of the subduction zone is more than twice as active as the northern. The 22 quakes limited to the southern segment ranged between 8.0 and 8.6 magnitude on the Richter scale. Those 19 that opened the entire rift ranged between 8.7 and 9.2.

(Scientists have discovered the Cascadia subduction zone is more complex than they thought. This video also includes a computer simulation of a 7.0 magnitude quake in downtown Seattle.)

Devestation from the tsunami resulting from the Tohoku quake.

Devastation after the Tohoku quake and tsunami.

For the sake of context, the 2011 Tohoku quake, strongest ever measured in Japan, that triggered the meltdown of the Fukushima nuclear plant and killed over 18,000 people, had a magnitude of 9.0. Scientists calculate the San Andreas fault is incapable of a quake larger than 8.2. Since the Richter scale is logarithmic, an 8.2 magnitude quake, though still potentially devastating, would release only 6% of the Tohoku quake’s energy.

Yet even an 8.0 quake will ravage the three major Northwest urban centers of Seattle, Vancouver and Portland. A tsunami will inundate the length of the coast. Up to 150,000 tourists crowd the beaches on summer weekends. A total of ten million people are at risk.

(A full, 48 minute BBC documentary on Pacific Northwest megaquakes.)

Most structures in the region were built prior to strict seismic codes. Until 1994, few could withstand a 9.0 quake. Ian Madin directs the Oregon Department of Geology and Mineral Industries. He estimates that 75 percent of the state’s structures – buildings, bridges, dams, overpasses – cannot withstand a major quake. A 2005 study shows even a 6.7 quake in Seattle would result in 39,000 collapsed or badly damaged buildings and 7,700 dead or severely injured.

As for a megaquake, FEMA’s best case scenario is 10,000 dead, assuming no beach tourists. What about the worst case? Ken Murphy, FEMA Regional Director, is glum. “Depending on when it happens, we’re talking numbers that this nation I’m not sure is really prepared to deal with.”

The New Madrid and Wabash Valley Seismic Zones: Hidden Danger Where The Mississippi and Ohio Rivers Meet

(Gripping first-hand accounts from those experiencing the great quakes of 1811 and 1812.)

Four earthquakes, estimated between 7.0 and 8.6 magnitude, jolted the New Madrid seismic zone between December, 1811 and February, 1812. The first of these quakes was powerful enough for the shaking to awaken people in New York City, a thousand miles away. It rang church bells in Richmond, Virginia and forced people to flee their homes in Lebanon, Ohio.

The quakes were so strong, one temporarily made the Mississippi River flow backwards.

From Cairo, Illinois, the 150 mile long, New Madrid fault system extends south, roughly along the banks of the Mississippi River into Kentucky, Missouri, Tennessee and Arkansas. When combined with the nearby Wabash Valley seismic zone, straddling the southern border of Illinois and Indiana, it encompasses an area six times larger than the San Andreas fault zone.

Many scientists consider the Wabash Valley seismic zone a branch of the New Madrid fault zone. “This whole region of New Madrid and the Wabash Valley seismic zone became a rift zone about 750 million years ago when the continent almost broke apart,” according to Michael Wysession, a seismologist at Washington University in St. Louis.

Wysession thinks the earthquakes of 1811 and 1812 transferred stress from the New Madrid faults to those of the Wabash Valley. Douglas Weins, also a seismologist at Washington University, agrees. “The strongest earthquakes in the last few years have come from the Wabash Valley Fault, which needs more investigation.”

Wysession explains that seismic waves can be felt 10 times farther in the Midwest than the West since the rock is far older and more brittle. “Let’s face it, St. Louis is the biggest city in the region of both faults, and the Wabash Valley Fault is closer to us.” Increased seismic activity there is bad news for nearby Indianapolis too, and even Chicago.

(“What if that same earthquake were to strike the Midwest today? The lives of at least 11 million Americans would be in peril.”)

FEMA  warns in a 2008 report of “the highest economic losses due to a natural disaster in the United States,” from a major quake in the New Madrid fault zone. It predicts “widespread and catastrophic” damage across Alabama, Arkansas, Illinois, Indiana, Kansas, Kentucky, Mississippi, Missouri, Oklahoma, Texas, and particularly Tennessee. Dams and levees would rupture. Thousands would die.

3,500 would die in a 7.7 magnitude quake, according to a 2009 study commissioned by FEMA. 7.2 million would be displaced. It would severely damage Memphis and St. Louis.

The safety of nuclear power plants is yet another huge concern. The media spotlights reactors threatened by the San Andreas fault, especially the Diablo Canyon Power Plant and the San Onofre Nuclear Generating Station. Yet the US Geological Survey (USGS) reported in 2010 that nine out of ten reactors at highest risk are located in the East, Midwest and South.

(Floating nuclear plants, located several miles offshore, would eliminate the risk from earthquakes and tsunamis. Ocean water would provide an unlimited heat sink to cool nuclear rods.) 

Seqouyah Nuclear Plant.

Seqouyah Nuclear Plant.

The Sequoyah Nuclear Generating Station is a case in point. Less than 300 miles of “old and brittle” rock seperates the eastern Tennessee power plant from the New Madrid fault system. Not much for a seismic zone capable of noticeably shaking the ground a thousand miles away. The USGS now ranks the Sequoyah reactors 1 and 2 as the fourth most at-risk for a core breach that would expose the public to radiation.

So what’s the near-term risk for a major quake? The US Geological Survey estimates a 25 to 40 percent chance of a 6.0 to 7.0 earthquake in the New Madrid seismic zone by 2060. A 2008 report by the Mid-America Earthquake Center at the University of Illinois asserts a 90 percent probability.

Scientists do agree, however, on a long history of megaquakes in the New Madrid seismic zone. Archeological studies show quakes of similar intensity to those of 1811-12 struck around 300 C.E., 900 C.E. and 1450 C.E. Evidence of liquifaction near the zone dates as far back as 4800 B.C.E. Liquifaction occurs when a large magnitude quake makes seemingly solid ground behave like a liquid.

Taking Personal Responsibility for Earthquake Preparedness

(This 23 minute documentary discusses the impact of a megaquake on Vancouver. Experts and survivors discuss what to do in a quake, and how you should prepare for the aftermath. Expect no outside help for at least three days.)

Infrastructure in the United States has been crumbling for decades. Governments hesitate to divert tax revenue into proactive safety measures addressing what most people wrongly consider a remote risk.

A small preparedness kit.

A small preparedness kit.

Stricter building codes, increased enforcement and increased preparedness training for the public and emergency services in at-risk areas are all important. Yet, as the Tohoku megaquake proved in Japan, the most quake-prepared nation on earth, government policy is still no substitute for personal responsibility.

Take the time to research the seismic risks where you live and work. Since that is where you likely spend most of your time, it is also likely you will be there when the big quake hits. Was your home or office built to withstand the stress? Are you at risk from liquifaction or mudslides?

You can bolt appliances to the floor, remove hazards such as glass display cases, and even retrofit the foundation of your house to isolate it from a quake’s jarring. If your residence or workplace is constructed of unreinforced masonry, most at-risk for collapse, you would be wise to move or work elsewhere.

Develop an evacuation plan in case of a tsunami or quake. Drill yourself and your family. Set up an emergency kit, useful for more than just earthquakes. Know how to turn off your gas and water mains.

Fast moving shock waves spread out from an earthquake’s epicenter before the slower, more damaging shocks hit. Dogs and other

Japan's earthquake early warning system. Two or more sensors detect fast moving P-waves. (Top image.) Warnings are sent to broadcast media and phone companies. (Bottom image.) They, in turn, send emergency warnings to the public before slower, dangerous S-waves arrive.

Japan’s earthquake early warning system. Two or more sensors detect fast moving P-waves. (Top image.) Warnings are sent to broadcast media and phone companies. (Bottom image.) They, in turn, send emergency warnings to the public before slower, dangerous S-waves arrive.

animals perceive this and become agitated. Scramble to the nearest safe place. You will have from a few seconds to several minutes warning, at most. The United States lags in early-warning technology, used throughout much of the tectonically active Pacific Rim.  It detects those early, fast shock waves, then sets off warning messages and broadcasts, giving people valuable seconds to seek safety. Those in charge of operating rooms, trains, power stations and other potential hazards can react to forestall danger.

Preparedness is an insurance policy. Legal or not, would you forego auto liability insurance if statistics showed you only had a one percent chance of needing it? Experts say there is a much greater possibility of a megaquake in certain regions. Be prepared.

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