The Earthquake Threat to North America

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The Earthquake Threat to North America

Submitted: August 12, 2012

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Submitted: August 12, 2012

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TheEarthquake Threat to North America

All of us hear about earthquakes occurring and how they can cause massive destruction and trigger tsunamis. But what exactly is an earthquake, and what causes them? What is the relationship between earthquakes and tsunamis? What geographic locations are more susceptible to earthquakes than others, and why?

For starters, an earthquake in simple terms is the Earth’s natural means of releasing stress. When the Earth’s plates move against each other, stress is put on the lithosphere. When the stress is great enough, the lithosphere breaks or shifts. Imagine holding a pencil horizontally and applying force to both ends by pushing down on them; the pencil would eventually bend. After enough force was applied, the pencil would break in the middle, releasing the stress you put on it. The Earth’s crust works the same way. As the plates move they put forces on themselves and each other, and when the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake.

So what are Earth plates? The scientific term is tectonic plates which are two sub-layers of the earth’s crust (lithosphere) that move, float, and sometimes fracture and whose interaction causes continental drift, earthquakes, volcanoes, mountains, and oceanic trenches.

It is no surprise that earthquakes can cause mass destruction, in fact they trigger tsunamis as well. A tsunami is a series of waves that are generated by an undersea disturbance such as an earthquake. From the area of the disturbance, the waves travel outward in all directions. The time between wave crests may be from five to ninety minutes, and the wave speed in the open ocean averages 450 miles per hour. Tsunamis can reach heights of more than 100 feet. As the waves approach the shallow coastal waters, they appear normal and the speed decreases. Then as the tsunami nears the coastline, it can grow to great height and smash into the shore, causing much destruction.

I decided to interview my friend whom resides in Corona, California which is in Riverside County and is situated near the Southern segment of the San Andreas Fault zone. He has lived in California for over twenty years and experiences trembles often. My interview went as follows:

1) What is it like living in a place like California, where earthquakes occur often?

“When you first move to California or when you first realize about earthquakes you are fearful of the earthquakes. After you have been through a few you put it in to perspective of only being concerned with a large one.”

2) Are you ever worried that you might be seriously hurt in an earthquake?

“The thought of being hurt in an earthquake has entered my mind however it is no more or less than being hurt in a car.”

3) Do you fear one day you might lose your house due to an earthquake?

“That thought is always on your mind. The building standards in California are to help reduce that chance so the newer your house is the better it will stand up to an earthquake. The one thing you always need to remember is if the big one hits there is not a lot you can do to protect your house. When I lived in Colorado if a tornado hit my house not much I could do to stop from losing my house. If Mother Nature wants to redecorate we don't have many choices.”

4) Are you prepared for an earthquake?

“I am prepared for an earthquake but more importantly I am prepared for any natural disaster. Anyone who is not prepared for large natural events is rolling the dice and hoping not to face them. I have been through earthquakes fires, tornados, blizzards, ice storms, heat waves, without electrical power, riots and floods, and the one thing that is constant the more prepared you are the better your chances are of surviving. I always say chance favors the prepared mind.”

5) What sort of preparations have you made in the event an earthquake occurs?

“My kids and I have a plan on what we are to do and where we are to go. We have alternative routes to home from many of the places we go.”

6) Do you ever want to leave California solely because of the risks of earthquakes?

“It has crossed my mind however would you leave Colorado because of tornados or blizzards? Would someone leave Florida or Texas because of hurricanes? New York for crime? The Mississippi area for flooding? Wherever you go you have risks. You just need to manage the risks.”

7) Is there anything you would to share on the topic of earthquakes?

“You prepare as best you can and then you make a plan. At that point you are as ready as you can be. If you let this or other issues outside of your control influence your life you will be unhappy and no one will enjoy your company. You have to live for today and not worry yourself to death.”

End of interview

So, how do we know about the locations of fault zones and how do we know if one geographic location is more susceptible to an earthquake versus another location? It is a young science, and is called Seismology which is the scientific study of the waves produced by earthquakes. This study began in the mid-1800’s. The original instrument developed to measure seismic (earthquake) waves was called the seismograph. In fact, the first seismograph in North America was installed in 1897 at the Lick Observatory near San Jose, CA. It recorded the famous 1906 San Francisco Earthquake. There are now several types of electronic instruments that are responsible for monitoring the earth’s movement. Some are connected by radio transmitters to devices implanted in the ground near known faults, or cracks in the earth’s crust. Throughout North America, universities and government geological laboratories maintain seismic monitoring stations. These devices operate 24 hours a day, seven days a week to receive and record vibrations within the earth’s crust along with the earth’s surface. This allows experts to identify concentrations of earth movement activity and possibly identify where major quakes may occur in the future. However, this assumption may not always prove correct.

The locations of North American Hazard Zones might surprise you. Somewhere deep beneath the surface of North America may be a major unknown fault, whose sides are not moving. Yet tremendous stresses may be building up, which one day will result in a catastrophic earthquake in a region that is not prepared. The science of seismology has not developed sufficiently to identify all faults in all places.

The order of identified earthquake zones is ranged in known potential to produce major earthquakes are as follows:

  1. Aleutian Islands and Southern Alaska Seismic Zone. This region has several active volcanoes and frequent tremblers occur. The strongest earthquake ever recorded in North America, occurred in 1964 in the Prince William Sound near Anchorage, Alaska. It was a 9.2 on the Modified Mercalli Scale. Alaska experiences the most earthquakes of any state in the United States. In fact it has more per year than the combined total of the rest of the nation. Several islands off the coast of Alaska have active or dormant volcanoes.
  1. Southern California Seismic Zone. Several major faults crisscross this region. The most famous is the San Andreas Fault, but there are several others that go in several directions that also have potential to cause major damage. Tremblers occur often in this zone and it is likely residents of this region will experience a 6.0 or greater earthquake in his or her lifetime. The areas where earthquakes are most likely to occur include the mountainous northern part of Metropolitan Los Angeles and desert basin north of the border between California and Baja California. One of the reasons earthquakes cause so much damage in Los Angeles is because housing has been densely built on steep hillsides that are already prone to landslides.
  1. Northwest Pacific Coastal Seismic Zone. There are several active volcanoes in this region. It includes major cities of Vancouver, BC, Seattle, WA and Portland, OR. Geologists have determined that 41 mega-earthquakes have occurred in this region in the past 10,000 years. Some geologists have predicted that a mega-earthquake will hit the northern end of the zone in the next ten years (Seaside, OR to Vancouver Island, BC.) Earthquakes in this region often create tsunami’s which later strike Hawaii and Japan. This zone could possibly be ranked one or two in potential danger but still does not produce the frequent tremblers like Alaska and southern California.
  1. San Francisco Bay Area Seismic Zone. Several major faults run roughly parallel to the coastline of San Francisco. The most famous is the San Andreas Fault, but others could cause major damage also. San Francisco experienced a catastrophic earthquake in 1906 and another major one in 1989. The region experiences tremblers on a regular basis, but again not at the frequency of southern California or Alaska. However, it is likely the residents of this region will experience a 6.0 or greater earthquake in their lifetime.
  1. Yellowstone Basin-Grand Tetons Seismic Zone. During the past fifty years there have been five major earthquakes ranging between 6.0 to 7.5 that have occurred in this region. In fact, the odds are 100% that a resident of this region will experience a major earthquake in their lifetime. The presence of the Yellowstone Caldera is the cause of this region’s vastly heightened danger. It is a massive plum of magma that has pushed upward through the earth’s crust. Its presence near the surface is what causes the many geysers and hot springs in the Yellowstone Basin. If this caldera ever erupts, the effects would be apocalyptic for much of the northwestern United States.
  1. New Madrid Zone. There are a cluster of faults in Missouri, Arkansas, Tennessee and Illinois which cause frequent tremblers in this region. Two earthquakes in 1811 and early 1812 were some of the strongest known since Europeans occupied North America. Between 150 and 200 earthquakes occur in this zone each year; most are tremblers. However, major earthquakes seem to occur in intervals of about 200-300 years apart. Geologists do not fully understand the causes of the earthquakes in this region. As a result, they cannot make any solid predictions as to when another major earthquake will occur again.
  1. Charlevoix-Eastern Quebec Seismic Zone. This is the most active earthquake zone in eastern Canada. An earthquake occurs in this region on an average of every day and a half. The majority of quakes occur under the Saint Lawrence River, which apparently flows through a fault. Most are tremblers, but five major earthquakes have occurred here in historical times. A 7.0 quake in the late 20th century did extensive damage to Quebec City and upstate New York.
  1. Eastern Tennessee-Northwest Georgia Seismic Zone. This is a region that apparently was very active with earthquakes and volcanoes in ancient times, but presently mainly produces a high frequency of minor tremblers. In recent decades the largest earthquakes were 4.6 on the Modified Mercalli Scale. The earthquakes in this zone occur extremely deep in the earth’s crust; generally ranging from 5 to 10 miles down.
  1. Charleston, SC Seismic Zone. One of the worst earthquakes in the history of the United States occurred in the Charleston area in 1886. It was a 7.6 earthquake in a region that was assumed to be immune from earthquakes. However, tremblers still occur in the vicinity of Charleston. The probability of another major quake to occur in this area is still being debated by geologists.
  1. Upstate New York Seismic Zone. This zone is directly south of the Quebec Seismic Zone, but not as active. The largest quake recorded in New York State was a 5.8 event near Massena in 1944. Upstate New York experiences tremblers often but is also affected by larger earthquakes in Quebec. Presently, the potential for a major earthquake in this region has not been precisely calculated.

While the above zone’s are the most known and most dangerous, and have the capability of causing the most damage and experience the most tremblers, there are other parts of the United States that also experience earthquakes and in some cases have caused damage. One state I would like to focus on is Colorado, my home state. Although I am not a native I have lived in Colorado for majority of my life. I personally have not felt any earth movement but I have read many stories of earthquakes occurring that were strong enough to be felt by residents and have also caused significant damage, recently and historically.

While the Rocky Mountains make Colorado both famous and gorgeous it can be argued that the Rockies make Colorado dangerous. Anywhere where there are mountains, there are faults. In fact that is how mountains are slowly formed, through repeated earthquakes. We know that earthquakes occur on faults; the problem is that we do not know where the fault lines are. Many of Colorado’s fault lines are near the Rocky Mountains. But it is what we do not see that makes predicting earthquakes impossible.

A pretty significant earthquake occurred in Northridge Los Angeles a few years ago that caused a lot of damage and destruction which was a shock to everyone as no one knew a fault existed in that area. This is the same for Colorado. In fact, Colorado’s worst earthquake occurred in Estes Park, Colorado in 1882. This was a 6.6 earthquake and caused a lot of damage including wiping out the power plant in Denver and cracked buildings in Boulder. At the present time experts still do not know where the fault line is located which caused the 6.6 earthquake in Estes Park in the 19th century. Colorado might be behind the curve when it comes to earthquake research but the chances of a large earthquake to occur in this region are very low. Colorado is certainly not out of the woods, as a 5.3 magnitude earthquake struck near Trinidad, Colorado in late August, 2011 which caused minor damages but no one sustained injuries.

For many years the main focus has always been on the Ring of Fire which is an area where a large number of earthquakes and volcanoes erupt in the basin of the Pacific Ocean. The Ring of Fire runs between the Kermadec trench all the way around to the Peru-Chile trench, measures 40,000 in kilometers, and is in the shape of a horseshoe. This area has been silent for three centuries and the attention has now been shifted to what is known as the Cascadia Subduction Zone which is yet another large fault but runs parallel to the Pacific coast of North America. This earthquake is capable of the mass destruction that occurred in Japan just over one year ago which triggered one of the most destructive tsunamis in history, and killed over fifteen thousand people. It is not a question of what happened in Japan will happen in North America, the question is when.

Anyone who wonders about earthquakes will most likely think of The San Andreas Fault that is approximately 810 miles and runs through California. The fault was identified by Andrew Lawson, a UC Berkeley geology professor in 1895. The San Andreas Fault is divided into three segments, The Southern, Central and Northern segments. The Southern segment of the fault is capable of causing an 8.1 magnitude earthquake which would kill thousands of people in Los Angeles, San Bernardino, Riverside, and other areas. The Central segment does not experience earthquakes as with the Southern segment, instead the central segment experiences aseismic creep which causes surface displacement along a fault, and does not cause an actual earthquake.

It is very frightening to me that earthquakes can cause so much destruction. They can cause power surges, phone wire line crashes, bridge collapses, roadway damage, and unfortunately death. Another thing that is frightening is that scientists are still trying to figure out how Japan, the world’s most earthquake-ready nation was taken so much by surprise when the Tohoku earthquake and tsunami struck. They were hit by an earthquake approximately twenty-five times more powerful than experts predicted in that part of the country. The fact is, if scientists had looked far enough back in geologic time, they would have learned that earthquakes and tsunamis as big as Tohoku have occurred in Japan before.

The Cascadia subduction zone is just as much of a threat to the west coast of North America. It was first thought, that the Cascadia fault was not capable of causing a massive earthquake. Scientists now know they are wrong. The Cascadia zone is a crack in the Earth’s crust, about sixty miles offshore that runs eight hundred miles from northern Vancouver Island to Northern California. This fault is also part of the well-known Pacific Ring of Fire. This is a zone that has several tectonic plates, and if they collide it will create enormous stress build up causing the rocks to fracture, and the fault to rip apart in a giant earthquake. Interestingly, the Cascadia is classified as the quietest subduction zone in the world because geologists cannot find any evidence of major earthquakes in all of recorded history.

There are several theories as to Cascadia’s silence. One of the possibilities is a very alarming one. It is possible the fault is merely an ominous pause. Meaning, these two slabs of the Earth’s crust have been jammed up against each other and locked together by their friction for many, many years. If this is true, tons of stress and strain has been building up that only a massive earthquake could relieve. It can cause the same kind of earthquake Japan saw in 2011, a magnitude 9 or higher. If an earthquake occurs, it can cause multiple and deadly tsunami waves across the Pacific and trigger destructive shock waves across a larger area of land than California has ever seen.

While there are geographical locations more prone to earthquakes than others in our nation, the truth is that earthquakes occur in many parts of the United States, more than people realize. Some believe a massive earthquake will strike our nation in the near future and it is said the effects would be apocalyptic for much of the northwestern United States. While we have sophisticated equipment that monitors and records earthquakes and helps experts narrow down locations that are more susceptible to earthquake occurrences; it is still very difficult for experts to precisely predict when an earthquake will strike a particular region. It is not a question of what happened in Japan will happen in North America, the question is when.

Works Cited

Jerry Thompson from the Extreme Earth special issue, Discover Magazine; published online March 13, 2012.

Andrew Cowper Lawson (July 25, 1861-June 16, 1952); Wikipedia June 28, 2012.

Earthquakes along the Cascadia and San Andreas Faults May Be Linked, Affecting Risk To San Francisco Bay Region, ScienceDaily (Apr. 3, 2008).

FEMA; http://www.ready.gov/earthquakes, July 23, 2012

U.S. Geological Survey; http://www.usgs.gov, July 26, 2012

Colorado Earthquakes; http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0005idz.php,August 23, 2011.

Definitions

Earthquake - A sudden slipping or movement of a portion of the earth’s crust, accompanied and followed by a series of vibrations.

Modified Mercalli Scale - Developed in 1931 by the American seismologists Harry Wood and Frank Neumann. This scale, composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals. It does not have a mathematical basis; instead it is an arbitrary ranking based on observed effects)

Lithosphere - On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.

Fault - The fracture across which displacement has occurred during an earthquake. The slippage may range from less than an inch to more than 10 yards in a severe earthquake.

Plate tectonics - is a scientific theory that describes the large-scale motions of Earth's lithosphere. The theory builds on the concepts of continental drift, developed during the first decades of the 20th century. It was accepted by the geoscientific community after the concepts of seafloor spreading were developed in the late 1950s and early 1960s.

Magnitude - The amount of energy released during an earthquake, which is computed from the amplitude of the seismic waves. A magnitude of 7.0 on the Richter scale indicates an extremely strong earthquake. Each whole number on the scale represents an increase of about 30 times more energy released than the previous whole number represents. Therefore, an earthquake measuring 6.0 is about 30 times more powerful than one measuring 5.0.

Seismic Waves - Vibrations that travel outward from the earthquake fault at speeds of several miles per second. Although fault slippage directly under a structure can cause considerable damage, the vibrations of seismic waves cause most of the destruction during earthquakes.


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