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Seismic Reports
and Discussions

Earthquakes in Alabama? - Northern and North-Central Alabama Seismicity

"Though the Earth Be Moved" - The 1964 Great Alaska Earthquake

Anatomy of a Mega-Quake - The Great Tohoku Earthquake of 2011

World Trade Center Disaster Seismic Signatures

Earthquake Weather - Fact or Fiction?

The World's Largest Recorded Earthquake

The Seismic Signature of Tornadoes

World Trade Center Disaster Seismic Signatures

September 11, 2001, New York City, USA

The terrorist attacks against the United States and the World Trade Center (WTC) in New York City on the morning 
of September 11, 2001 not only created shock waves in the political and social fabric of the United States, but also formed a 
tragic backdrop to a most interesting seismic study of artificially-generated seismic signals and how these compare to the
seismic signatures from earthquakes.  Ground vibrations associated with the collapse of the World Trade Center buildings were
recorded across five states, and as far away as 428 km (265 miles) from New York City.  The terrorist attacks produced a complex
array of signals generated both from the initial impact of the airplanes, to the collapse of the WTC Towers and subsequent
collapses of neighboring buildings.  As will be shown, the North Tower collapse produced a 
seismic signature equivalent to a magnitude 2.3 earthquake. 

WTC Bombing

Actually, several seismic stations in the greater New York City area recorded signatures of ground vibrations from the terrorist attacks
that morning in lower Manhattan (see Figure 1).  The closest was the Lamont-Doherty Cooperative Seismic Network (LCSN)
station PAL located at Palisades, NY.   Lamont-Doherty operates 34 seismograph stations in seven Mid-Atlantic and New England 
states. The network has been in operation since the early 1970s.

NYC Seismic Stations

Figure 1
Seismic Stations Near Greater New York City
(from: http://911research.wtc7.net/mirrors/guardian2/wtc/seismic/WTC_LDEO_KIM.htm)

Numerous seismic signals were recorded at station PAL, first a smaller signature when the airplanes impacted the WTC towers,
and then much larger indications as the towers collapsed.  The timeline for the two building impacts and subsequent three collapses
of the North and South Towers and the smaller WTC Building 7 begins at approximately 12:46:26 UTC (8:46:26 EDT) and shows
Richter Scale Magnitudes from  0.9 to 2.3 (see Figure 2).

WTC Bombing Times

Figure 2
WTC Impacts and Collapse Times and Richter Scale Magnitudes
(from: http://www.ldeo.columbia.edu/LCSN/Eq/20010911_wtc.html

The seismogram from station PAL shows that the WTC North Tower collapse was the largest seismic source and had a local
magnitude ML 2.3 (see Figure 3).  The seismogram begins at 12:40 UTC and each trace in the seismogram is 30 minutes long.
The North Tower was subject to the first impact (8:46 EDT) and the second collapse (10:28 EDT, magnitude 2.3), while the
South Tower saw the second impact at 9:02 EDT and collapsed first at 9:59 EDT (magnitude 2.1).

WTC Bombing Seismograms

Figure 3
PAL Seismogram from WTC Impacts and Collapses, 11 Sept 2013
(from: http://911research.wtc7.net/mirrors/guardian2/wtc/seismic/WTC_LDEO_KIM.htm

Overall, six stations within the greater Metropolitan New York region (Fig. 4) recorded the two tower collapses. Unfortunately, no
seismic recordings of ground motion are currently known to exist at or very close to the WTC complex.  Figure 3 shows the North
Tower collapse signature at stations PAL, BRNJ, TBR, MANY, and ARNY, indicating the different times (in seconds) after 
the collapse at which the seismic signals were detected at the several stations.

WTC Bombing Various Seismograms

Figure 4
World Trade Center North Tower Collapse Seismograms at Five Local Stations
(from: http://911research.wtc7.net/mirrors/guardian2/wtc/seismic/WTC_LDEO_KIM.htm

The signals at PAL from the North Tower collapse and a small felt earthquake that had occurred beneath the east side of Manhattan
on January 17, 2001 were of comparable magnitude (see Figure 5).  However, the character of the two seismograms is quite
different.  Note that distinct P and S body wave responses are seen only for the earthquake; this is usually the case in comparing
the seismic signatures of man-made ground disturbances and those recorded in earthquake events.

Compare WTC Bombing and Small Quake

Figure 5
Magnitude Comparison of WTC North Tower Collapse and Small Earthquake
(from: http://911research.wtc7.net/mirrors/guardian2/wtc/seismic/WTC_LDEO_KIM.htm)

Earthquakes of magnitude 2.3 are not known to cause any structural damage in buildings.  In the eastern U.S. that threshold is 
believed to be close to or above ML 4 to 4.5.  It has been estimated that the total gravitational potential energy associated with the
collapse of each of the WTC towers was at least 10xE11 Joules. The energy propagated as seismic waves for a magnitude 2.3
earthquake is about 1.8xE8 Joules (see
http://alabamaquake.com/energy.html), or less than about five thousandths of the total 
potential energy release involved in the collapse. 

So, only a very small portion of the total gravitational potential energy in the building collapse was converted into seismic waves. 
Instead, most of the energy went into the deformation of building structures as they fell, and the formation of rubble and dust.
Accordingly, local observations of the WTC tower collapses did not indicated that ground shaking was a major contributor to the
collapse or damage to surrounding buildings.  

The seismic energy of a ML 0.7 to 0.9 energy release computed for the building impacts is but a tiny fraction of the total kinetic
energy (about 2 x 10xE9 Joules) of each aircraft. Additionally, the energy associated with the combustion of the fuel in each fully-loaded
aircraft was estimated to be roughly 10xE12 Joules; most of this energy was expended in the large fireballs (visible in TV images) 
and in the subsequent burning that ignited material in each tower prior to and during their collapses.  It follows that less than a millionth 
of the total fuel energy in the attacking airplanes was converted to the radiating seismic waves. 

Twelve years ago, the World Trade Center in New York City was brought down in a senseless act of terrorism.  But now,
a new WTC is rising to once again be a part of the New York skyline.  A look back at those awful events of 11 September 2001 paints
an intriguing view of geology and seismology as we learn more about the earth and its structure.






Earthquake Weather
Fact or Fiction?

“A heat wave in San Francisco is rare, but when one occurs, it usually lasts three days… Tuesday, April 17, 1906,
was the first of three such days, and by evening it was still breathlessly hot… I heard tales that horses in their stalls
were restless much of that night.  This, linked with the unseasonable weather - "earthquake weather" - some were to
call it, would be remembered by the superstitious as portents of impending disaster… (on Wednesday morning,
April 18th) I was awakened by a violent shaking of the house accompanied by a roar and the sound of cracking wood…
I could hear the crash of falling bricks outside..."


San Francisco 1906 Quake

Folklore applies the term "earthquake weather" to a sultry, ominously uneasy period said to precede large earthquakes. Scientists
have generally dismissed suggestions that weather could have anything to do with the tremendous underground forces associated
with an earthquake, as tectonic plates are shifting and rubbing against one another.  Yet, many people who have ample experience
with seismic events insist that quakes and weather are somehow connected.

“Earthquake weather” is said to be signaled by close, oppressive conditions: hot and humid weather, with thin, wispy clouds
appearing overhead and no predicted rain.   Stories of “earthquake clouds” describe long, straight cloud forms that appear for days
over a fault before it finally shakes.  One theory is that a squeezing motion of the earth prior to a quake generates electric currents
that decompose trapped ground water and release hydrogen and oxygen ions into the air, with these ions then producing the clouds
and the unusual calm characteristic of “earthquake weather.”

Earthquake Weather Clouds

In the 4th century B.C., the philosopher Aristotle proposed that earthquakes were caused by winds trapped in caves.  Small quakes
were thought to have been caused by air pushing on the cavern roofs, and large ones by the air breaking through the earth’s surface. 
This idea said that because a large amount of air had been trapped for some time underground, the “earthquake weather”
would be hot and calm before a quake.  And ever since, many people have pointed to various signs
of the weather as being linked to earthquakes.

Studies have surmised that long periods of calm, quiet weather, with very high atmospheric pressure, could result in destabilization
of the ground, triggering landslides and quakes.  Some have drawn conclusions that more quakes tend to occur in the winter than
the summer, usually when there is a surge of unusually warm weather.  Malcolm Johnston, a research geologist at the USGS Menlo
Park California Science Center, said many earthquakes occur at depths of six miles or greater - far removed
from the surface
weather conditions.  "People have argued that you're heating the earth...but we're talking no more than a couple of meters into
 the crust," Johnston said. "Further down than that, you wouldn't even know it's a hot day outside."

Another theory says that it's not the temperature changes causing earthquakes, it's that the high-pressure weather system creating
the sultry, oppressive heat is pushing on the ground, disturbing the underlying faults.  Johnston said that's unlikely.  Such a pressure
change underground, he said, would be miniscule: only on the order of one part in 100 million.  And he said that the increased
pressure on faults would actually make it harder for an earthquake to occur, not easier.

Low Pressure Weather

Alternatively, some recent investigations have suggested an association of large, fast-moving low-pressure (stormy) weather
systems with initiation of ground events, theorizing that "...when there is less force exerted upon the ground, the upward movement
of air and water molecules in the soil would serve to reduce the friction that usually holds the soil or rocks in place, and could trigger
certain types of slides and quakes..."(study lead William Shultz, USGS, Denver, Colorado). 

Still, it is generally accepted in the scientific community that there is no such thing as "earthquake weather."  Statistically, there is an
approximately equal distribution of earthquakes in hot weather, cold weather, rainy conditions, etc.  While large, dynamic surface
weather conditions might correlate to the occurrence of some very shallow geological events, tectonic plate shifting has been
occurring rather consistently deep in the earth for millions of years, irrespective of those weather conditions. 

Some observers may yet hold to the common misconception (dating back to the ancient Greeks) that earthquakes are more likely
to occur during hot and dry weather; but the large majority of quakes originate many miles underground, and so are not likely to
 be influenced by surface weather conditions.

The World’s Largest Recorded Earthquake

It is referred to as the "Great Chilean Earthquake" and the "1960 Valdivia Earthquake.” 
With an assigned magnitude of 9.5, it is the largest earthquake ever recorded by modern instrumentation.

At 3:11 pm (19:11 UTC) on the afternoon of Saturday, 22 May 1960, the devastating magnitude 9.5 (Mw) event struck
 in west-central Chile.  Severe damage from shaking occurred in the epicentral Valdivia-Puerto Montt area.  Although
there are many different casualty estimates for this earthquake ranging from a low of 490 to a high of "approximately 6000,"
most historical reports place this figure at 1655 deaths.  Much of the damage and many of the casualties were due to large
tsunamis which caused damage along the coast of Chile and in many areas across the Pacific Ocean, where fatalities
 from this quake were recorded as far away at the Philippines.

Chile M9.5 Earthquake Map
Magnitude 9.5 Earthquake Epicenter Location in West-Central Chile

The epicenter was near Lumaco, Chile, some 570 kilometers (km), or about 350 miles (mi) south of Santiago, with Temuco being
 the closest large city, while Valdivia, Chile was the most affected city.  An estimated 2,000,000 people were made homeless,
and $550 million in damage was totaled, in central-southern Chile.  The tremor caused local tsunamis that severely damaged Chilean
coastal areas with waves up to 25 meters (m), or about  82 feet (ft) in height.  The tsunami  moved rapidly across the Pacific Ocean,
causing additional damage all across this wide region.  Waves as high as 10.7 m (35 ft) were recorded some 10,000 km (6,200 mi)
from the epicenter.  Seismologists monitored world-wide micro-seismic vibrations that, “like the ringing of a bell,”
persisted in the earth for days after the quake had occurred.

Video: February 2010 Report by CBS News on Chilean M9.5 Earthquake
Video: February 2010 Report by CBS News on Chilean M9.5 Earthquake

Just off the Pacific coast of Chile and the rest of South America, the Nazca tectonic plate is
subducting beneath the edge of the South America plate. The convergence associated with this
subduction process is responsible for the uplift of the Andes Mountains, and for the active volcanic chain
present along much of this area.  Relative to the South American plate, the Nazca plate is moving
north-northeastwards at a rate that varies from about 80 millimeters per year in the south to
approximately 65 millimeters per year in the north, giving rise to volcanic activity, crustal deformation,
and earthquakes all along the western coastline of South America.

Numerous large earthquakes have occurred in the western Chilean coast region before and after the historic quake on May 22nd. 
The M9.5 event was a megathrust earthquake that had a focal depth of 33 km (20.5 mi).  It was estimated to have produced a
rupture zone some 1000 km (612 mi) in length, extending from Lebu, to Puerto Aisen, one of the longest tectonic ruptures ever reported.

Chilean 1960 Earthquake Damage
Damage in Chile near M9.5 Earthquake Epicenter

Land subsidence caused by the earthquake produced local flooding and permanently altered the shorelines of much of the
epicentral area in Chile.  Many landslides occurred Chilean hillsides.  A 1-1.5 m (3-5 ft) of ground subsidence occurred
along the Chilean coast from the south end of the Arauco Peninsula to Quellon on Chiloe Island.   As much of 3 m (10 ft) of
ground uplift occurred on Isla Guafo.  Many landslides occurred in the Chilean Lake District from Lago Villarica to Lago Todos los Santos

Coastal Damage in Chile from M9.5 Earthquake
Costal Damages Caused by Tsunami following M9.5 Earthquake in Chile

In the epicentral area, the town of Puerto Saavedra was completely destroyed by tsunami waves which reached heights
of 11.5 m (38 ft) and carried remains of houses inland as much as 3 km (2 mi). Wave heights of 8 m (26 ft) caused much damage
at the seaport town of Corral.

Chilean 1960 Earthquake Tsunami
Tsunami Movement Across the Pacific Ocean Following M9.5 Earthquake in Chile

Some 18 hours after the quake occurred, tsunamis caused 61 deaths and severe damage in Hawaii,
mostly at Hilo, where the wave runup height reached 10.6 m (35 ft).  The Hawaiian office of Civil Defense totalled
some $24 million in damages caused by the tsunami..

Chile M9.5 Earthquake Damage in Hawaii
Tsunami Damage in Hawaii from Chile 9.5 Earthquake

Waves as high as 5.5 m (18 ft) struck northern Honshu, Japan, about 22 hours after the quake had occurred.
 The tsunami destroyed more than 1600 homes in Japan, and left as many as 185 people dead or missing,
with an estimated $50 million in damage.

Another 32 people were dead or missing in the Philippines after the tsunami hit those islands.
Damage also occurred on Easter Island, and in the Samoa Islands.

Along the western coast of the United States, major damage was reported at Crescent City, and in the Los Angeles and
Long Beach harbor areas, where many small craft were set adrift and some were sunk in the incoming tsunami waves
which had a height reported to be 1.7 meters (5.6 feet).  Total damage was estimated at $500,000 to $1,000,000
on the west coast of the United States.

California Damage from Chile M9.5 Quake
Damaged Ship on California Coastline from Chile M9.5 Earthquake and Tsunami

On May 24th, two days after the earthquake had occurred, Volcan Puyehue erupted, sending ash and steam
 as high as 6,000 m (almost 20,000 ft)  The volcanic eruption continued for several weeks after the earthquake.

The M9.5 quake was preceded by four foreshocks larger than magnitude 7.0, including a magnitude 7.9 quake on May 21st
that had already caused severe damage in the Concepcion area.  Many aftershocks occurred following the May 22nd mainshock,
with five of these recorded at magnitude 7.0 or greater, through November 1, 1960.

The death toll from this huge earthquake was less than it might have been because it occurred in the middle of the afternoon
when much of the population was out of doors; because many of the local structures had been built to be earthquake-resistant;
and due to the several strong foreshocks in the area that had already made the population somewhat wary of additional quake activity.

Because the region is situated on a the long tectonic fault boundary between the Nazca and South American plates,
seismologists believe that it is only a matter of time until Chile once again suffers a "world-class" earthquake whose impact,
like the M9.5 event in 1960, will be felt around the world.

The Seismic Signature of Tornadoes

Scientists have long considered the possible connections between violent weather phenomena and low-frequency ground
vibrations detectable by seismographs.  In more recent years, several examples have been documented where the ground track
of a tornado near seismic stations has been correlated to unusual seismic activity recorded by the seismograph equipment.

A 1994 paper by researchers in Huntsville, Alabama and at the University of Alabama (“Tornado Detection Based on
Seismic Signal,” Tatom/Knupp/Vitton; 18 July 1994) discusses the mechanisms by which energy could be transferred to the
 ground by a tornado, resulting in patterns of local ground vibrations and low-frequency seismic surface waves which may be
detectable by seismographs in the area.  Though no specific examples of this energy transfer are described,
the paper nonetheless ponders the question of future research and development of suitable sensors.


In a 1999 study, micro-seismic noise levels were recorded in Ohio for some 2 hours prior to, and 30 minutes following,
a powerful EF4 tornado that touched down in a Cincinnati suburb on April 9th.  Seismologists were able to correlate
distinctive changes in the amplitude and envelope of low-frequency and high-frequency noise content in the data produced
by several local seismographs as the tornado approached on the ground nearby, and then continued out of the area.

In a related investigation, a scientist at NOAA’s Environmental Technology Laboratory at Boulder, Colorado, was working
with an acoustic sensor designed to detect low-frequency sound waves produced by an avalanche, when he witnessed the
 instrument detecting signals from a tornado passing some 14 miles away in the area.  In further studies of pickup of the
1-5 Hz sounds that tornadoes may generate, the avalanche observing system detected 27 other tornadoes, some as far
as 100 miles away (see “Scanning the Skies: A History of Tornado Forecasting” by Marlene Bradford).

A strong tornado touched down in a path from Henderson County, Kentucky
to Warrick County, Indiana on November 6, 2005, killing 25 people and
injuring many more, and causing extensive damage to homes and businesses. 
Ground vibrations that correlated to the time of the tornado were observed
on home-built equipment constructed by an amateur seismologist
at his residence in Evansville, Indiana.

More recently, in conjunction with the National Science Foundation’s “EarthScope” program, scientists from Indiana University
Bloomington participated in the deployment of an array of over 100 seismographs in the area around Harrisburg, Illinois. 
EarthScope seeks to cover the entire U.S. with a grid of detection devices to better understand seismic activity and the
potential for earthquake predictions.  Researchers liken EarthScope to “an upside-down telescope” that allows them to look
 into the Earth and gain a better understanding of seismic forces.

EarthScope USA

EarthScope Planned Seismograph Array Deployment
(Graphic Credit: Earthscope)

On February 29, 2012, a pre-dawn EF4 tornado passed through the Harrisburg area with estimated wind speeds
around 180 miles per hour, killing six and injuring over 100 people.  In the deployed array of EarthScope seismographs,
 three stations in southern Illinois showed unusual seismic activity during the time period when the tornado was passing
through the area, even though there were no earthquakes occurring at that time.

Intrigued by their data, the Indiana University scientists conducted a post-storm investigation and said in announcing
the results of their study, “The seismograms show a strong, low-frequency pulse beginning [before the tornado’s touchdown]
around 4:45 a.m. on February 29.  Our preliminary interpretation, based on other seismic records of tornadoes, suggests
that we were recording not the tornado itself, but a large atmospheric pressure transient related to the
large thunderstorms that spawned the tornadoes.”

29Feb12 Tornado Track
Deployed Seismographs and Approximate Path of February 29, 2012 Tornado
(Graphic Credit: Indiana University Bloomington)

Further analysis of the micro-seismic activity noted in seismograms recorded during the February tornado related
a change in atmospheric pressure prior to the tornado forming and touching down to the ground, to a small,
slow tilting of the ground at
the seismic stations that lasted for several minutes.  This might be visualized by imagining the
end of a vacuum-cleaner hose held close to the surface of a bedsheet or other thin fabric cover, and moved slowly across
the fabric while the vacuum is operating.  Note how the low-pressure area at the end of the hose created by the vacuum's
suction will lift up a small, local section of the fabric as the hose is moved.  A similar action might be imparted to the earth's
surface as the low-pressure area associated with a tornado's formation moves through the area.   

The scientists say this pressure-related signal might help better our understanding of atmospheric activity that takes place as
tornadoes are being formed.  One seismologist has asserted that because seismic signals can travel faster as in-ground
vibrations than the actual storm (seismic waves in the ground travel many times faster than do sound waves in the air),
a seismograph buried underground might give advance notice of an abrupt change in the local atmospheric pressure many
miles away: "There is a huge pressure difference differential between the center of the storm and outside of the storm and that
[an increased and decreased] weight on the surface of the earth. So it's compressing the earth differently.”

While these past examples and observations do show a connection between tornadoes and micro-seismic activity,
much more research remains to be done in this interesting area of earth science.  One day it may be possible to construct
algorithms that, through seismic observations, could work with advanced radar capabilities in the prediction of tornado
formation and paths.  However, compared to the study of a broad-area weather event such as a hurricane, the strong
effects of a tornado are seen in a relatively small straight-line area, and so a challenge facing researchers in the study of tornadic
seismic signatures is a need for suitable detectors that are found to be located along or near the storm’s path.  Continued work
 with programs such as EarthScope, that deploy more ground-truth instruments, may aid in addressing this need.  

"Though the Earth be Moved"
The 1964 Great Alaska Earthquake

…therefore will we not fear, though the earth be moved,
and though the hills be carried into the midst of the sea…  Psalm 46:2 (MSTC)

Acknowledging the 50th anniversary of the 1964 Great Alaska Earthquake, the United States 
Geological Survey released in 2014 a documentary video about that event.
The video is located at
https://www.usgs.gov/media/videos/1964-quake-great-alaska-earthquake, and highlights the impacts and
effects of the quake which, at magnitude 9.2,
is the largest recorded earthquake ever to strike in the United States.

“… at 5:36, a dozen miles deep, under the mountains north of Prince Williams Sound, the earth shifts and begins
to move… suddenly, the whole harbor at Valdez begins to empty, and drains almost dry… out in the Gulf of Alaska,
the ocean bottom plunges, then heaves upward a full 50 feet, and a wave starts racing to shore… now the tremor builds
and rips like lightning around the 500 mile arc… at 5:44, the seismic wave hits Seward… it strikes Kodiak later, first a
high silent tide, then a 40-foot monster  thundering up the channel… all the clocks have stopped at 5:36,
and so has everything else…”
 ( from the 1965 documentary film “Though the Earth Be Moved”)
It has been called the Great Alaska Earthquake, the Good Friday Earthquake, and the Portage Earthquake. 
The massive tremblor struck at 5:36 pm Alaska Standard Time, on Friday, March 27, 1964, in the northern part
of the Prince William Sound about 75 miles east of Anchorage, Alaska.  With a moment magnitude of 9.2, it remains
the largest earthquake seen in North America and the second-largest quake ever recorded worldwide.
The earthquake shaking lasted almost 4 minutes, triggering many landslides and avalanches in the area. 

Alaska Earthquake 1964 Anchorage 4th Street Collapse

Collapse of Fourth Avenue near C Street in Anchorage, Alaska

Good Friday Earthquake, March 27, 1964
(U.S. Army Photo)

Vertical ground displacement caused by the earthquake was seen over an area of about 200,000 square miles,
causing a maximum of about 38 feet of ground uplift to as much as 8 feet of subsidence, relative to sea level. 
On land, the shaking led to extensive property damage across a broad area of an estimated 100,000 square miles
of southern Alaska.  In the coastal waters, movement of the seafloor generated a major tsunami that had a major
impact on the southeast coast of Alaska, the Pacific Coast of British Columbia, and the west coast of the United States. 
The quake also caused at least five local landslide-generated tsunamis in the region within minutes after the
shaking began.  One eyewitness reported the water rising 15 feet in 5 seconds at Kodiak, Alaska. 

Total property damages due to the earthquake were estimated at some $350-500 million in 1964 dollars, a figure
equivalent to several billion dollars today.  Across south-central Alaska and surrounding areas, earthquake-generated
ground fissures, collapsing structures, and regional tsunamis led to a total of 131 deaths.  A very small number of fatalities
was attributed to the earthquake itself, with the large majority of deaths due to the ensuing tsunami.  Research conducted
after the earthquake indicated that the surface energy released by the shock was roughly equivalent to the detonation of
100 million tons of TNT, or the force of about 63,000 atomic bombs the size of the one
dropped on Hiroshima, Japan in 1945.

The city of Anchorage suffered the greatest damage to residences, commercial buildings, and infrastructure such as
paved streets and sidewalks, water and sewer mains, and electrical utility systems.  About 30 blocks of dwellings and
commercial buildings were damaged or destroyed in the downtown Anchorage area.  The schools in Anchorage were
almost completely destroyed.  Nine immediate deaths occurred in the local area: five in downtown Anchorage, three in
Turnagain Heights, and one at the International Airport.  The death toll in the region near the quake epicenter was unusually
small for an event of this severity, because of Alaska’s low population density (at the time), and because the quake
occurred on a holiday (Good Friday) when schools and businesses were closed, in the late afternoon when most people
were at home.  Also, the wood construction used for many area homes was more flexible than concrete, and could bend
more without collapsing.  Nonetheless, earthquake effects were substantial in many population centers, including
Anchorage, Chitina, Glennallen, Homer, Hope, Kasilof, Kenai, Kodiak, Moose Pass, Portage, Seldovia, Seward,
Sterling, Valdez, Wasilla, and Whittier.

Alaska Earthquake 1964 Airport Control Tower Collapse

Collapse of Anchorage International Airport Control Tower
Good Friday Earthquake, March 27, 1964 (FAA Photo)

The port of Valdez in Prince William Sound saw a massive underwater landslide that resulted in the deaths of 32 people
in the collapse of the Valdez city harbor and docks, and damages to the ship Chena that was docked there at the time. 
Southwest of Kodiak, some areas of land were permanently raised as much as 30 feet, while the ground level was
lowered significantly in some areas near the towns of Portage and Girdwood.  The area of subsidence covered some
110,000 square miles, including the north and west parts of Prince William Sound, the west part of the Chugach Mountains,
most of Kenai Peninsula, and almost all the Kodiak Island group.  With the subsidence and subsequent tidal inrush, people
living in the community of Girdwood and other areas relocated further inland, while the town of Portage was abandoned.

Alaska Earthquake 1964 Kodiak Tsunami Damage

Tsunami Damage at Kodiak, Alaska
Good Friday Earthquake, March 27, 1964 (USGS photo)

The quake-generated tsunami devastated many towns in coastal areas along the Gulf of Alaska, and left extensive
damage at Whittier, Seward, and Kodiak; at Alberni and Port Alberni, Canada; in British Columbia; and along the West
Coast of the United States.  The initial wave attained a speed of more than 400 miles per hour, and traveled a total of
some 8,400 miles.  A maximum wave height of 220 feet was seen at Valdez Inlet.  The village of Chenega was destroyed,
with 23 deaths recorded there, by the tsunami which measured 27 feet in height at that location.

Along the western coast the United States, the tsunami killed 12 people and caused an estimated 17 million dollars
in damage in California.  The wave flooded a large portion of Crescent City, killing 10 and causing approximately 15
million dollars in damage.  At San Francisco, the tsunami, though only about 3 feet high, caused an estimated 1 million
 dollars in damages in that area.  The State of Oregon saw four deaths and extensive damages to bridges, houses, cars,
 boats, and sea walls, due to the tsunami.  Across the wider northern Pacific region, tsunamis caused damage in Hawaii
and Japan, and there was further evidence reported from all over the earth of effects related to the quake. 

Seiche action (water sloshing in contained areas) caused minor damage in rivers, lakes, bayous, and protected harbors
and waterways along the Gulf Coast of Texas and Louisiana. The tsunami was recorded by tide gages throughout the
 Pacific, and sea level oscillations caused by the quake were recorded in Cuba and Puerto Rico.  Sloshing water was
observed in wells as far away as Africa.

Alaska Earthquake 1964 Epicenter Map

Epicenter Location and Tectonic Fault Zone
Good Friday Earthquake, March 27, 1964
(Original base map by Mapquest)

The earthquake was caused by a rupture in the crustal fault between the Pacific Plate and North American Plate
 near College Fjord in Prince William Sound.  This part of the “Pacific Ring of Fire” is a tectonic subduction zone,
with the Pacific Plate moving beneath the edge of the North American Plate at a rate of some 50 to 70 millimeters
per year, causing the crust of southern Alaska to be compressed and twisted under the strain.  Over time, some coastal
areas were being slowly depressed while others were raised up as the tectonic pressures increased along the locked
plate boundary.  On March 27th, the boundary could no longer sustain the stress, and, after a period that may have lasted
for centuries, the built-up strain and compression was relieved by the sudden slippage and resultant southeastward
movement of portions of coastal Alaska, as the North American Plate moved back over the subducting Pacific plate. 

The fault rupture began at an estimated underground focal depth of approximately 15.5 miles, north of
Valdez and the upper Prince William Sound, with the major area of uplift trending northeast from southern Kodiak Island to
Prince William Sound and continuing to the east of the sound.  Investigations indicate that,
from the underground focus,
the fault rupture also proceeded westward along the tectonic plate boundary over a distance of some 500 miles to an area
southwest of the Trinity Islands in the Gulf of Alaska.  The net result of the fault rupture and plate boundary slippage,
 in relieving the pressure built up for centuries, was a further movement of the Pacific plate underneath
the North American plate by an average of some 30 feet.

“Magnitude measurements varied, depending on the scale used. The reported Richter magnitudes
ranged from 8.4 to 8.6. (Later, it was found that the Richter didn't measure accurately beyond 8.0.)
The surface-wave magnitude (Ms) was 8.6. The moment magnitude (Mw) was 9.2.  Most of that energy
was absorbed by the ocean and land, but much man-made construction couldn't withstand the remainder.”

(from “The Great Alaskan Quake of 1964” by U-S-History.com)

Thousands of aftershocks were recorded by seismologists in the months following the M9.2 earthquake’s main shock. 
During the next day, 11 aftershocks with magnitudes greater than 6.0 were registered.  In the next three weeks,
nine more aftershocks were observed, and smaller aftershocks continued to be detected in the region for more than a year.

Alaska Earthquake 1964 Portage Townsite Abandoned

Abandoned Portage, Alaska Townsite
Good Friday Earthquake, March 27, 1964 (National Geographic Photo)

Scars from the devastating earthquake can still easily be seen in the landscape of southern Alaska’s coastal areas. 
Virtually destroyed in the earthquake, the town of Portage was abandoned.  With damage being furthered by time and
the elements of Mother Nature, evidence of the few remaining buildings at the Portage townsite are slowly disappearing
among the new marshy growth of what was once dry ground.  Trees that once grew here are located by dead trunks,
having been killed by the salt-water marsh created when the land subsided and ocean waters flooded the area during the
earthquake.  Since that time, continuing tectonic processes are again building stresses in the crustal material underlying the
region, with a growing potential for another significant earthquake in this seismically active part of the world.



“Though the Earth Be Moved” Documentary Film (1965), United States Office of Civil Defense
United States Geological Survey (USGS)

Alaska Earthquake Information Center

University of Arizona Geosciences Program

University of Southern California Tsunami Research Group

The Great Alaskan Quake of 1964

Anatomy of a Mega-Quake

A brief look back at the Great Tohoku Earthquake, March 11, 2011

Update, 04 March 2014: "In a poll conducted by Kyodo News, more than fifty percent of the 42 mayors of towns,
villages and cities from the Tohoku region of northeastern part of Japan struck by the March 2011 earthquake and 
tsunami believe that recovery has slowed down or halted ... even if residents have evacuated to keep away from the
radiation leaking out of the nearby power plant, no [new] developments have been made ... while deaths from the 
March 2011
disasters reached 15,884 according to the National Police Agency, 2,636 people are still unaccounted
for by February 10,
just short of three years after they happened..."  - Japan Daily Press, March 03, 2014

The ground in the Tohoku region of the northern island of Honshu, Japan, began
rumbling on March 9, 2011, with a series of large earthquakes in the area measuring
over magnitude 6 and peaking at magnitude 7.2.  This was not considered highly
unusual in Japan, given the region’s familiarity with earthquakes. 
But two days later, everything would change.

At 2:46 pm (Japan local time) on the afternoon of March 11, 2011, a massive magnitude 9.0 earthquake, the world’s fifth
largest seen since 1900, struck off the northeastern coast of Honshu.  Strong ground shaking lasted three or more
minutes in some places.  The offshore earthquake generated a major tsunami wave that resulted in widespread
property damage and destruction in the nearby coastal areas of Honshu, and the deaths of many thousands
 living in the region.  The tsunami damaged the Fukushima Nuclear Power Plant, disabling the emergency
generators needed to cool the reactors and leading to nuclear meltdowns and extensive radiation leaks. 

Tohoku M9.0 2011 Destruction

A staggering scene of destruction was left behind when the earthquake shaking and tsunami subsided. 
At least 15,703 people had been killed, 4,647 were missing, 5,314 were injured, and over 130,000 were
 displaced, along the entire east coast of Honshu from Chiba to Aomori.  Property damages included at least
332,395 buildings, 2,126 roads, 56 bridges and 26 railways destroyed or damaged in these areas.  The total
economic loss in Japan was estimated at 309 billion US dollars.  Outside of Japan, one person was killed
and several houses were destroyed at Jayapura, Indonesia, by a tsunami with a wave height of 2 m.  In the United
States, one person was killed south of Crescent City, California, and several boats and docks were destroyed or
 damaged along the coast with estimated damages exceeding $50 million, by a tsunami with a
recorded wave height of 2.47 m.

Tohoku M9.0 2011 Tsunami

The Tohoku M9.0 earthquake resulted from thrust faulting on or near the tectonic plate subduction zone boundary
along the Japan Trench just off the eastern coastline of Honshu, where the Pacific Plate is slowly moving back
into the earth’s mantle beneath the edge of the North American Plate.  Strong earthquakes that result from the
subduction of tectonic plates usually occur on plate segments that rupture singly or in combination, and in the past,
 relatively small areas of plate segments in the Japan Trench have slipped sequentially, causing notably
damaging earthquakes.  However, during the March 11, 2011 Tohoku quake, several large-area
subducting plate segments Japan slipped simultaneously, something that may not have previously occurred in
that place for over a thousand years.

Tohoku M9.0 2011 Map

GPS units operating during the quake sampled ground movement in the epicentral area at 1 second increments
during the earthquake, showing that a 4 m eastward expansion, and a 1 m coastal subsidence, of the Honshu
 mainland occurred during the plate slippage sequence, and was accompanied by the radiation of 50-100 km
wavelength seismic surface waves.

Tohoku M9.0 2011 Japan Trench

The graphic above shows an East-West section through the Honshu coastline, with the Pacific Plate
subducting at some 90 millimeters/year (USGS reports place this movement at a rate of 83 mm/yr) beneath the
North American Plate, and the location of the main plate boundary rupture ending close to the shore at 30-40 km depth. 
The rupture is shown moving 20 m along the fault, while some further studies have modeled this at 30-40 m. 
The main fault rupture caused the coastal subsidence (lowering the pre-earthquake shoreline by up to 1 m) and the
 undersea uplift which created the subsequent devastating tsunami.  Some more extensive studies have suggested
that the plate movement was more dramatic than originally modeled, with a horizontal slip of around 50 m and
vertical movement of up to 10 m.

Tohoku M9.0 2011 Seafloor Crack

The quake opened up cracks as wide as 2 m (6.3 ft) in the seafloor, where clam beds once lay. 
A photograph of the seafloor (above) was made on August 10, 2011 off the coast of Japan after the earthquake,
showing a 20 cm ( 8-in) wide opening that stretches for tens of meters or more in a north-south direction at an
undersea depth of 3,218 m (10, 558 ft).  The depth of the crack itself could not be determined.

The seismic moment, a measure of the total amount of energy released by the quake,
was calculated to be
3.9E+22 Joules, equivalent to the detonation of some 617 Hiroshima-sized
atomic bombs.  Only about 0.005%
of this total energy, or some 1.9E+18 Joules, was calculated
to have been radiated as seismic waves.

The entire fault rupture process was estimated to have lasted about three minutes, with some 70% of the seismic
moment released during the first half of the rupture duration time, when the fault disturbance remained confined in a
100–150 km wide slab segment in the northern part of the fault.  The rupture process then spread in a southwest
 direction, eventually covering an area approximately 450 km long and 150 km wide.

The Great Tohoku Earthquake has been classed as “an infrequent catastrophe,” and has become one of the most
extensively-examined earthquakes in modern times.  Some studies have found that, based on seismic modeling
results and GPS data, the horizontal movement along the tectonic plate interface near the epicentral area represents
roughly 400 years of accumulated tectonic strain in the Japan Trench region.  The earthquake’s fault motion and
 intensity far surpassed that of other quakes of the 20th century in this area, none of which were as intense as
 magnitude 8.  A similar quake may have occurred on July 13, 869, when historical records show that the area
east of Sendai was apparently engulfed by a large tsunami.

Tohoku M9.0 2011 Aftershocks

In the weeks since the main shock, more than a thousand aftershocks were recorded in the area, about half of
which registered magnitude 5 or greater.  Aftershocks from the quake continued for many more months.  Impacts will
be felt for many years in the Tohoku region due to the damages caused by the earthquake shaking and tsunami. 
As the Pacific Plate  maintains its process of subduction back into the Earth’s mantle, repeated adjustments of stress
levels in the region will occur along the involved tectonic plate boundaries, and more earthquakes are to be expected
in this area.  As usual, the exact location and timing of future quakes cannot be specified, and large earthquakes
will continue to occur in this region, just as we have seen in past years.



Cooperative institute for Research in Environmental Sciences at the University of Colorado at Boulder

 United State Geological Survey (USGS)

 Incorporated Research Institutions for Seismology (IRIS)

Southern California Earthquake Center (SCEC)

Earthquakes in Alabama?
Northern and North-Central Alabama Seismicity

Earthquakes are actually fairly common in the eastern half of the United States,
with many of these seen in the New Madrid Seismic Zone (NMSZ) which is situated
along the Mississippi River, roughly centered at New Madrid, Missouri.

We might see light to moderate shaking in northern Alabama if a strong earthquake struck in the NMSZ.
The NMSZ is known for a series of three strong earthquakes (with estimated magnitude between 7 and 8) that struck in 1811-1812.
The Unites States Geological Survey (USGS) estimates the chance of having an earthquake in the NMSZ with a magnitude 6
or larger in the next 50 years is 25 to 40 percent, and the chance of seeing an event similar to one of the 1811–1812
sequence occurring in the next 50 years is about 7 to 10 percent.

In terms of tectonic plate interactions, the NMSZ is known as an intraplate zone, located far away from a tectonic plate boundary.
Earthquakes occur here in the large network of faults, buried beneath hundreds to thousands of feet of mud, sand, and rock,
which formed about 500 million years ago when the region was stretched in the northwest-southeast direction.
Additional faults have formed much more recently as crustal rifting/thinning, sediment loading, and downwarp processes
have continued in the NMSZ.  Now the region is slowly undergoing east- west shortening, and the reactivation of old,
subterranean faults within this rift system is thought to be responsible for the continuing seismicity of the zone,
with most earthquakes occurring at depths of 4-12 kilometers.

But closer to home, we in Alabama could also be affected by another seismically active area in our region,
the Southern Appalachian Seismic Zone (SASZ), which roughly follows the Appalachian Mountains
from southwestern Virginia into the northeastern corner and central part of Alabama (see Figure 1).  The USGS says that,
“the Southern Appalachian Seismic Zone is one of the most active earthquake zones in the eastern United States.”

SE_USA Seismic Zones
Figure 1
Seismic Zones of the Southeastern United States
Image courtesy of the Geological Survey of Alabama

 The SASZ is also an intraplate seismic zone similar to the NMSZ.  The SASZ has released moderate levels
of seismic energy for many hundreds of years.  The tectonic setting for SASZ is crustal uplift/compression,
as opposed to the rifting/downwarp processes seen in the NMSZ.  No active seismic faults are known
to reach the surface in the SASZ, although the area is laced with many ancient faults that developed
as the Appalachian Mountains formed several hundred million years ago.  While many surface and buried faults
have been located in the region, numerous unknown smaller and more deeply buried faults remain undetected,
and these all have an ongoing potential for randomly located small-to-moderate earthquakes.

 Some Alabama Earthquake History

As part of the SASZ, the geology of north and north-central Alabama includes numerous buried and surface faults,
and the state has seen many small earthquakes, and some 20 larger events, since shortly before the beginning
of the 20th century (see Figure 2). The recorded history shows that the earthquakes have been small-moderate,
never reaching above a magnitude of 5.1. This size of earthquake tends to cause local damage only near the quake epicenter,
with shaking felt in areas further away.  Major Alabama events include a quake seen in 1916 in the Birmingham area,
and one that occurred near Fort Payne in 2003.

North Alabama Faults 1886-2012
Figure 2
North and North/Central Alabama Seismic Faults and Earthquake Epicenters
Image courtesy of the Geological Survey of Alabama

Alabama’s Largest Earthquake
The largest earthquake in Alabama’s recorded seismic history struck on October 18, 1916,
on an unnamed fault located east of Birmingham.  The strongest effects were felt at Easonville, in the Irondale area.
Near the epicenter, chimneys were knocked down by the strong quake, windows were broken, and frame buildings
were "badly shaken."  Shaking by the earthquake was felt by residents in a seven-state area
covering some 100,000 square miles.

North Alabama Earthquakes
On April 29, 2003, an earthquake with magnitude of 4.9 (some reports say 4.6) struck in DeKalb County,
a few miles northeast of Fort Payne.  The focal depth of the quake was determined to be approximately 15 km (9.3 miles).
It caused some minor landslides in the area, and caused a shutdown of the underground water supply for the town
of Valley Head.  Shaking from the earthquake caused some minor building damage in Fort Payne, including broken windows,
minor cracks in masonry, and broken or collapsed chimneys.  The quake effects were felt across several southeastern states.

An earthquake with an estimated 3.8 - 4.0 magnitude occurred just north of Huntsville on August 12, 1959.
Felt over a small area of southern Tennessee and northern Alabama, it shook bricks from chimneys at Hazel Green,
and damaged another chimney and a newly constructed concrete block building at Meridianville.  Buildings were shaken
violently at New Sharon, with canned goods being knocked from shelves and frightened residents fleeing from their homes to
the outdoors.  The shaking cracked plaster walls and knocked grocery goods from store shelves in Huntsville.

In more recent years, the historical record shows that several small quakes have been seen in the Huntsville area.
These include a pair of events, measured at M2.2 and M2.5, in 2011; a magnitude 3.9 quake that occurred
a few miles east of Huntsville in 2001; and a M3.0 quake seen east of Huntsville in 1984.

 In April 1957, a small earthquake occurred east of Guntersville.  Though it was felt from northern Alabama to Georgia
and Tennessee, and resulted in some cracking of walls and movement of some small objects from shelves and tables,
it caused little substantial property damage.  According to local reports, there was “minor damage to several chimneys;
one report of cement steps cracked in two; and several small cracks in walls. Table-top items tumbled to the floor."

In early March 2013, two magnitude 2.7 earthquakes occurred in Walker County, Alabama, near the city of Jasper,
at similar focal depths in the range of 4-5 km (2-3 mi).  The seismogram of one of these quakes, the M2.7 event registered
on March 1st, is shown as recorded at the AlabamaQuake seismic station in Huntsville, Alabama,
at an epicentral distance of some 126 km (see Figure 3).

Walker County M2.7 01Mar13
Figure 3
AlabamaQuake Seismogram
M2.7 Earthquake, Walker County, Alabama, March 01, 2013

In Figure 4 below, the three most recent Walker County quake epicenters have been superimposed onto a
close-up portion of the larger North and North-Central Alabama Faults and Epicenters map seen above in
Figure 2.
It does not appear that any particular significance can be immediately attributed to the occurrence
of  these two events, even in such close location and time proximity, given the rich history of such small
quakes in this area.  Note the appearance of these three most recent quakes near identified buried faults
 traversing the area, and the proximity of these new quakes to numerous other events seen in the area.

Walker County Closeup - 3 Earthquakes
Figure 4
Location of Three Most Recent Walker County, Alabama Earthquakes
Base map image courtesy of the Geological Survey of Alabama


The northern and north-central Alabama region is not considered to be in a high-risk area for significant
damages caused by earthquakes.  However, our proximity to the New Madrid Seismic Zone calls for a need to
be aware of the potential for local impacts due to a strong earthquake occurring in that regionally-nearby area.
And the Southern Appalachian Seismic Zone which extends across much of our area is primarily responsible for
the low-level seismicity and periodic small earthquakes, with occasional minor damages, seen in this part of the state.

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