In a depth of 1,800 miles, mysterious 'mountains' float along Earth´s core-mantle layer

In a depth of 1,800 miles, mysterious 'mountains' float along the D''-core-mantle boundary since the birth of Earth.

How seismic waves are reflected or scattered inside Earth has long shown that the planet's interior is not uniform, but can be subdivided into various layers. Earth's crust is composed of less dense crystalline rocks, like granite and gabbro. Earth's mantle is composed of magnesium, iron, and silicon dioxide and it's estimated to make up 38% of Earth's volume. The outer core is liquid, composed of very dense elements, like iron, nickel, with traces of sulfur and oxygen. The inner core is solid, almost a pure iron-nickel alloy, maybe even with a crystalline structure (making it possibly Earth's largest crystal). 

Seismic waves have also shown that along the boundary layer between mantle and core, strange blobs or plumes, rise up for many thousands of miles. One hypothesis explains the blobs as remains of partially molten tectonic plates, sinking from Earth's surface into the mantle. The melting plates can´t sink into the much more dense core. Melting completely along the boundary, the remains of the plates form blobs of material, slowly floating back to the surface and driving there the motion of Earth's tectonic plates. 

Another, more recent, hypothesis explains the blobs as remains of Earth's primordial crust. During Earth's formation a first, primitive crust developed on the cooling surface. Parts of this crust sunk into the mantle, too dense to rise, the material boils slowly there since Earth´s formation. Computer simulations presented during the European Geosciences Union conference in Vienna suggest that the plumes are composed of crystallized material, as the long permanence of the material under high pressure and temperature makes it possible to grow grains of minerals, some inch in diameter. As mineral grains form rocks, the plumes are composed of rocks, making them miles-high 'mountains' (sort of...), even if at a temperature of 5,000°C.

The now presented simulations show the distribution of temperature and grain size, with the hotter (yellow to white), coarse-grained (yellow-red), plumes floating along the core and rising into the mantle:

 

Love Can Move Mountains

January 11, 1996 a single seismograph of the Geological Survey of Canada buried in a quiet wooded area on central Vancouver Island started to record an unusual strong seismic signal – slowly, but perpetually increasing in amplitude over time it was recorded only at this station – nearby station (located within a radius of 20km) didn´t show any movements – this was no ordinary 6.8 magnitude earthquake as could occur along the Cascadia Subduction Zone.

Fig.1. Seismogram showing a segment of the unusual seismic signal, from CASSIDY & WHITFORD 1996.

After one-half hour there was a sudden increase in intensity of the signal. The geologists at the Pacific Geoscience Centre in Sidney, 125 km distant of the seismograph position and monitoring the unusual signal, decided to call the police and a nearby a public school to check the situation.

Meanwhile the signal amplitude continued to increase – and an ever increasing number of puzzled technicians and scientist gathered around the monitoring equipment at the Geoscience Centre. At 4:28 PM – 43 minutes after the unusual recording was first noted – the signal suddenly stopped.

Later it was confirmed that it was exactly at 4:28 PM that the police officers and the school staff arrived at the seismograph site, where they found a young couple, trembling in passion and the source of the recorded Love Waves and supposed man-made quake…

Bibliography:

CASSIDY, J.F. & WHITFORD, A. (1996): Unusual “Love Waves” Recorded Above the Cascadia Subduction Zone. Seismological Research Letters. Vol. 67(6): 49-51

From Nukes to Ship Disasters - how Forensic Seismology helps to understand Catastrophes

On July 25, 1946 the United States detonated the first underwater nuclear weapon in history – code name “Baker” – at the Bikini Atoll. The explosion generated a gas bubble that pushed against the water, generating a supersonic shock wave which crushed the hulls of nearby target ships as it spread out. Seismic waves of this test were observed at seismograph stations around the globe and it was realized that these waves could be used to detect and potentially characterize a nuclear explosion.

Fig.1. Photography of the underwater “Baker” nuclear explosion of July 25, 1946 showing the white sphere of water and vapour formed by the shock wave of the explosion (image in public domain).

The U.S. performed also the first fully underground explosion – code name “Ranier” – that was detected by about 50 seismic stations; however, it was confused in part with a “normal” earthquake.
 

With the ban of nuclear weapon (well, sort of…) testing in the year 1958 it became necessary to install an effective worldwide monitoring system. Three years later the set-up of the WorldWide Standardized Seismographic Network (WWSSN) began and in 1966 almost 112 stations were working in the monitoring project “Vela“. Vela provided a large quantity of supplementary seismic data used to answer three questions: Where is the seismic event located? What is the source type (artificial or natural) of the event? How large is the event?

“It appears increasingly doubtful that an atomic-weapons test of significant dimension can be concealed either underground or in outer space. A five-kiloton nuclear explosion in an underground salt cavern near Carlsbad, N.M., in December was clearly recorded by seismographs as far away as Tokyo, New York, Uppsala in Sweden and Sodankyla in Finland. The seismograph records included tracings of the ‘first motion,’ considered critical in distinguishing between earthquakes and underground explosions.” from “Scientific American“, February 1962

The signature of a natural earthquake shows a distinct pattern: a seismometer will first detect the Primary and Secondary Waves, followed by the more destructive Surface or Rayleigh Waves.
Seismic P Waves are compressional waves, similar to sound waves in the air. Secondary or Shear (S) Waves are transverse waves, like those that propagate along a rope. A sudden explosion generates a “sphere” of compressional waves travelling in all directions. In contrast an earthquake is caused by the sliding of rocks along a fracture and it will generate shear waves concentrated in a certain direction. Therefore an explosion will show a strong and sudden signal of P-waves, with a similar signal recorded by all the seismometers collocated around the explosion. An earthquake will show a more complex pattern, depending of the position of the seismometer, characterized by strong S-Waves and R-Waves.
Also an underground explosion does not generate very strong surface waves as a natural earthquake does.

Fig.2. Schematic seismogram with Primary (P; compressional waves), Secondary (S; shear waves), and Rayleigh (R; surface waves) phases for an artificial blast and a natural earthquake.

As every atomic explosion will generate a unique pattern, distinct from natural earthquakes, seismology is a reliable tool to control the ban of nuclear test and to supervise countries that still test atomic weapons.

The information recovered from seismograms of nuclear blasts can be applied in forensic seismology also to study detonations of common explosives. Most spectacular cases in the last years comprise the reconstruction of the Oklahoma City bombing in 1995 (see this abstract by HOLZER at the AGU meeting in 2002) and the investigation in the explosion on the Russian submarine “Kursk” in 2000 (see KOPER et al. 2001; the blog “About.com Geology” hosts many other examples).

Seismic waves can be generated not only by shear movements along faults or by the expansion of plasma (nuclear device) or gas (conventional device) during an explosion, but also by the impact of objects with the ground.
Seismic signals were already used to identify the location of rock-falls and recent research suggests that the signals can help to characterize the dynamics and volume of a landslide, Dave Petley discusses the significance and use of seismograms in various posts published on his “Landslide blog“.

The analysis of seismic waves provided also insights on what happened September 11, 2001 in New York. Seismograph stations around the city recorded the signals generated by the aircraft impacts and the subsequent collapse of the two towers of the World Trade Center (the Lamont-Doherty Cooperative Seismographic Network provides a rich collection of datasets of the seismic activity around N.Y.). The collapse of the south tower generated a signal with a magnitude of 2.1 and the collapse of the north tower, whit a signal of magnitude 2.3, was recorded by 13 stations ranging in distance from 34 to 428 km.
Also these seismograms show a distinct pattern if compared to the pattern caused by a natural earthquake. There are no P or S Waves, but the impacts of the buildings on the ground generated a sudden peak of short-period Rayleigh Waves.

Fig.3. Seismic recordings at the seismograph station Palisades (N.Y.) for events at World Trade Center on September 11, distance of station from Ground Zero ~ 34 km. Note that impact 1 and collapse 2 relate to the north tower, and impact 2 and collapse 1 apply to the south tower. Expanded views of the first impact and first collapse shown in red. Figure from KIM et al. 2001, published here according to the Usage Permissions granted by AGU & authors.

The seismograms show also that the impact and explosion of the two airplanes generated a relative small amount of seismic energy. This confirms the observation that the collapses of the two towers were not a direct result of the impacts, but caused by the weakening of the supporting structures of the buildings due the subsequent fires.

Most energy of the collapses was dispersed into the deformation of the buildings and the formation of rubble and dust, only a small portion of potential energy was converted into seismic waves. The generated 2.1 and 2.3 M earthquakes were too weak to destabilize nearby buildings, most damage was done by the kinetic energy of the debris and the displaced air.

Also the collision of the cruise ship “Costa Concordia” on January 13, 2012 was recorded by the seismograph station “Monte Argentario“, situated on the Italian mainland. From the eyewitness testimony and the Automatic System of the ship the time of collision with a submerged rock was estimated at 20:45 (UTC). This time is confirmed by a sudden peak in the seismogram at 20:45:10 (the seismograph station is distant 18 km from the site of the collision, the seismic waves needed almost 3-4 seconds to travel this distance). The seismogram shows also after the impact the “noise” generated by the hull of the ship grinding along the rocky substrate.

Fig.4. Seismogram recorded at the station “Monte Argentario” (Italy) showing the seismic waves generated by the impact of the “Costa Concordia” on January 13, 2012 20:45 (UTC). An accurate analysis of “The seismic wake of “Costa Concordia” (23.01.2012) can even specify the speed of the ship at the moment of the collision. Figure used with permission and taken from the post “The earthquake of the Costa Concordia” by Italian seismologist Marco Mucciarelli, published January 21, 2012 on his blog “terremoti, sismologia ed altre sciocchezze“.

Bibliography:

ANDERSON, D.N.; RANDALL, G.E.; WHITAKER, R.W.; ARROWSMITH, S.J.; ARROWSMITH, M.D.; FAGAN, D.K.; TAYLOR, S.R.; SELBY, N.D.; SCHULT, F.R.; KRAFT, G.D. & WALTER, W.R. (2010): Seismic event identification. WIREs Computational Statistics Vol.2, July/August: 414-432
KIM, W.-Y.; SYKES, L.R.; ARMITAGE, J.H.; XIE, J.K.; JACOB, K.H.; RICHARDS, P.G.; WEST, M.; WALDHAUSER, F.; ARMBRUSTER, J.; SEEBER, L.; DU, W.X. & LERNER-LAM, A. (2001): Seismic Waves Generated by Aircraft Impacts and Building Collapses at World Trade Center, New York City. EOS Vol.82 (47)

KOPER, K.D.; WALLACE, T.C.; TAYOLR, S.R. & HARTSE, H.E. (2001): Forensic seismology and the sinking of the Kursk. EOS, Vol.82 (4): 37

Paleoseismology of the Anatolian and Caucasus Region

"The people of Behura fled from my weapons into the mountains of Uschkiani and Banni. I surrounded part of them and killed all. The others that could flee were burned by the earth god Teischeba."
Description of the military campaign of king Argischti I in 780-756 B.C.

Turkey is characterized by two main strike-slip fault systems - the North Anatolian Fault (NAF) and the East Anatolian Fault - that in the Caucasus region merge together in a complex tectonic system dominated by compressional thrust faulting. 

Devastating earthquakes of the last decades occurred mainly along the dextral North Anatolian Fault that forms the plate boundary between the Anatolian and Eurasian plates. This is also a densely populated region with the city of Istanbul as one of the most important harbours of the Mediterranean Sea. 

May 10, 1566 the cities of Rossana and Constantinople (modern Istanbul) were hit by an earthquake that caused the collapse of buildings. Some 50 years earlier (October 10, 1509) Constantinople had been affected by an even worse disaster, killing 13.000 people. 

During the 20th century seismic activity apparently moved along the NAF from the east to the west, in 1999 two strong earthquakes hit the city of Izmit, killing 17.000 people.

In Armenia the strongest earthquake since centuries occurred December 7, 1988, it destroyed the city of Spitak and killed 25.000 people.

Fig.1. Simplified tectonic map of the Caucasus region with the locations of important earthquakes - the recent earthquake at Van, the earthquake of Spitak and the historic earthquake of Behura. Various sections of the North Anatolian Fault show a progressive younger activity from the east to the west (colour coded). According to some models this could suggest that stress is released following the fault system and that Istanbul could be hit again by a stronger earthquake in the future.

The region around Lake Van was repeatedly hit in the present and the past by strong earthquakes. Cronicles report of havoc and destruction in the 4th century and again in the 10th century, in 1976 an earthquake in the Van Province caused 4.000 victims.
One of the oldest earthquakes in the Caucasus region was inferred from historic descriptions and confirmed by geologic evidence -it dates back to more than 2.700 years. 

A French-Armenian team of paleoseismologists searching for suitable sites for their research discovered on aerial photographies the ruins of the ancient city of Behura.
Paleoseismology tries to collect evidence for earthquakes based on both archaeological as geologic proxies to improve the knowledge of the seismic history of a region. Knowing this history of a region can help to estimate the time-intervals occurring between earthquakes of a certain magnitude.
Ancient documents refer to a city located in the area around the Lake Sevan that was conquered in 780 to 756 B.C. by the great king Argischti I, the description of the siege is curious, mentioning fire, ash and clouds (send supposedly by the earth god Teischeba) helping destroying the city. Maybe this is the description of a volcanic eruption accompanied by earthquakes. Nearby the site relatively unweathered and therefore probably young lava flows coming from the volcano Porak were discovered,
In Behura the excavation of a trench revealed a complex stratigraphy of soils, a displaced wall, scree deposits and younger soils, suggesting that the city was in fact destroyed by an earthquake.

Bibliography:

HERVÈ, P. & KARAKHANIAN, A. (2001): Der Untergand von Behura. Spektrum der Wissenschaft -Dossier 2 "Die Unruhige Erde": 31-35
JACOB, K. (2006): Istanbul - Warten auf den großen Schlag. Bild der Wissenschaft 2: 48-53

Earthquakes and the rapture

Peter Hadfield debunks again all the religious crap and quacks misusing geologic phenomena to promote their delusions:

Fig.1. Boxplot-diagram showing earthquake magnitude after Richter in the years 1900-2002 - the mean value of every year shows no significant trend 1900-1960, since 1960 the monitoring system incorporates more and weaker earthquakes, therefore the step - but again the mean value of all events per year show no trend, also stronger earthquakes do not surpass the years of the first half of the 20th century…all the self-proclaimed prophets obviously didn´t even bother to control the information aviable on the site of the U.S.G.S.

And now more prophets....

The Geisha and the Tsunami

More than a month has passed since the earthquake and the Tsunami that devastated the coast of north-eastern Honshu.
After the first shock people begin to ask if the extent of destruction and number of victims (more than 14.000 confirmed dead and 12.000 people missing) could be predicted. There are various hinds that can help to produce a risk map - there is geological evidence like fossil Tsunami deposits, there are in prehistoric time maybe myths and legends surviving in oral traditions, there are in historic time written stories in chronicles, scientific observations and measurements in charts, there are monuments, but there are also the eyewitnesses' reports of survivors.

In various newspapers and online media the accounts of many survivors of the last Tohoku tsunami were reported, the story of the geisha Tsuyako Ito is remarkable because it provides us with a scale how often Japan was hit by such disasters - even in the span of a single human life.
With her 84 years she experienced three tsunamis who hit the city of Kamaishi and as a girl she had listened to her grandmother's tales of the great 1896 tsunami.

"My grandmother said that a tsunami is like a wide-open mouth that swallows everything in its path, so that victory comes to those who run away as fast as possible."

The German newspaper "stern" published this old photography of a performance by Tsuyako Ito, she lost everything in the devastating Tsunami except her memories - and she promised not to surrender.

Her mother carried her on her back to safety at the time of Ito's first tsunami in 1933. This time, her fourth and "most frightening" tsunami, she was saved by an admirer who carried Ito on his back to higher ground.

The warnings of such experiences unfortunately last only a short time, according to the Japanese Yotaru Hatamura who studied ancient traditions about Tsunamis in Japan:

"It takes about three generations for people to forget. Those that experience the disaster themselves pass it to their children and their grandchildren, but then the memory fades," he said.

After the earthquake that devastated Tokyo in 1923 and San Francisco in 1906 the opportunity to rebuild the cities following antiseismic principles was abandoned to provide a fast reconstruction.

We shouldn´t ignore or forget...

Online Resources:

ONISHI, N. (08.04.2011): Geisha survives with help from an admirer - Guardian of a local culture has lived through four tsunamis. (Accessed on 25.04.2011)

April 18, 1906: The Great San Francisco Earthquake

"San Andreas Fault
Moved its fingers
Through the ground
Terra cotta shattered
And the walls came
Tumbling down

O, promised land
O, wicked ground
Build a dream
Tear it down

O, promised land
What a wicked ground
Build a dream
Watch it all fall down"
"San Andreas Fault" sung by Natalie Merchant

 

One of the firsts to note something unusual where the sailors of the transport ship "Wellington" entering the bay in early morning of April 18. 1906, the captain reports that the ship "shivered and shook like a springless wagon on a corduroy road" even if the sea was as "smooth as glass".
At the shores of Ocean Beach the worker Clarence Judson was taking a swim in the sea when he was grabbed by a strong current and sucked into the deep - only with great effort he reached the coast:

"I tried to run to where my shoes, hat and bathrobe lay, but I guess I must have described all kinds of figures in the sand. I thought I was paralyzed. Then I thought of lightning, as the beach was full of phosphorescence. Every step I took left a brilliant iridescent streak. I jumped on my bathrobe to save me."

In Washington Street the police sergeant Jesse Cook observed a terrifying spectacle:

"The whole street was undulating. It was as if the waves of the ocean were coming toward me, billowing as they came..[]"
"Davis Street split right open in front of me, … A gaping trench. . . about six feet deep and half full of water suddenly yawned and sprang up on the sidewalk at the southeast corner while the walls of the building I had marked for my asylum began tottering. Before I could get into the shelter of the doorway those walls had actually fallen inward. But the stacked-up cases of produce that filled the place prevented them from wholly collapsing."

The Geography professor George Davidson awoke from the tumult coming from the street, he grabbed his wristwatch on the desk and noted the length of a first quake - 60 seconds- and the second - again 20 to 40 seconds - and the time that later will be the official date of the great earthquake of San Francisco: 5:12.

Many people were still asleep and killed in their beds, those who escaped gathered in the streets - despite the earthquake most of the city seemed still intact and surprisingly quiet.

In 1906 San Francisco was a great and ambitious, but also corrupt and infamous city with more than 400.000 inhabitants; it had experienced an incredible growth since 1848 thanks to the discovery of gold in the rivers of California. Now it was an important harbour to the Pacific Ocean and modern trade place, many shops sold the newest technologies in cameras and film equipment. The earthquake of San Francisco will become the first natural disaster of its magnitude to be so well documented by photography and motion picture footage (even in colour).
This growth and achievements were however possible only by cheap and fast construction methods and so most buildings in San Francisco were not exceptionally stable and made of wood.
San Francisco had burned to the ground six times in the past century and experienced stronger earthquakes in 1865 and 1868 when 30 people died. However the modern automatized fire department and equipment - horse driven and steam powered water pumps - was believed to be capable to fight every fire.Fig.1. "Earthquakey Times", a caricature by Ed Jump of the October 8. 1865 earthquake in San Francisco. While he was working as a newspaper reporter in San Francisco, Mark Twain experienced the earthquake which he describes in his 1872 book "Roughing It."
"It was just after noon, on a bright October day. I was coming down Third Street. The only objects in motion anywhere . . . were a man in a buggy behind me, and a [horse-drawn] streetcar wending slowly up the cross street. . . . As I turned the corner, around a frame house, there was a great rattle and jar. . . . Before I could turn and seek the door, there came a terrific shock; the ground seemed to roll under me in waves, interrupted by a violent joggling up and down, and there was a heavy grinding noise as of brick houses rubbing together. I fell up against the frame house and hurt my elbow. . . A third and still severer shock came, and as I reeled about on the pavement trying to keep my footing, I saw a sight! The entire front of a tall fourstory brick building on Third Street sprung outward like a door and fell sprawling across the street, raising a great dust-like volume of smoke! And here came the buggy-overboard went the man, and in less time than I can tell it the vehicle was distributed in small fragments along three hundred yards of street. . . . The streetcar had stopped, the horses were rearing and plunging, the passengers were pouring out at both ends. . . . Every door, of every house, as far as the eye could reach, was vomiting a stream of human beings; and almost before one could execute a wink and begin another, there was a massed multitude of people stretching in endless procession down every street my position commanded. . . . For some days afterward, groups of eyeing and pointing men stood about many a building, looking at long zig-zag cracks that extended from the eaves to the ground..."

Police sergeant Jesse Cook was the first to report a fire at April 18. in a grocery in Clay Street, some hours later there where already fifty in the entire city. The fire fighters realized horrified that the water pipers in the underground were broken and the hydrants in the city useless. The firestorm rages in the city for three days and will be responsible of 90 percent of the 28.000 destroyed buildings.

The journalist Arnold Genthe is thrilled by the scenery and the devastation caused by the approaching fire, unfortunately he discovers that his camera was damaged during the quake.

"I found that my hand cameras had been so damaged by the falling plaster as to be rendered useless. I went to Montgomery Street to the shop of George Kahn, my dealer, and asked him to lend me a camera. "Take anything you want. This place is going to burn up anyway." I selected the best small camera, a 3A Kodak Special. I stuffed my pockets with films and started out...."
He will take some of the most famous photos in history.

Fig.2. "Looking Down Sacramento Street, San Francisco, April 18. 1906."

The owner of "Hotaling´s Whiskey" in Jackson Streets decides to remain and fight the flames - he pays 80 men to sprinkle 5.000 barrels of whisky with water pumped out from the sewer system. Later he will mock all those who claim that the earthquake was send by god by coining a new advertising slogan:

"If, as some say, God spanked the town, for being over frisky - why did He burn the churches down an save Hotaling´s Whiskey?"

Army troops were soon ordered into the city to help in the fire fighting and prevent panic and looting. The lack of water forced to desperate measures - by blasting of entire quarters to create firebreaks it was hoped to stop the flames, however many explosions ignited even more fires. Despite martial law was never proclaimed, the major authorized policeman and soldiers to shoot looting persons - "Obey orders or get shot" was the grim warning on some improvised signboards.
Guion Dewey, a businessman from Virginia, wandering onto the streets of downtown San Francisco minutes after the quake experienced the best and worst of human behavior, as he later reported in a letter to his mother:

"I saw innocent men shot down by the irresponsible militia. I walked four miles to have my jaw set. A stranger tried to make me accept a $10 gold piece. I was threatened with death for trying to help a small girl drag a trunk from a burning house, where her father and mother had been killed. A strange man gave me raw eggs and milk . . . (the first food I had had for twenty-two hours). I saw a soldier shoot a horse because its driver allowed it to drink at a fire hose which had burst. I had a Catholic priest kneel by me in the park as I lay on a bed of alfalfa hay, covered with a piece of carpet, and pray to the Holy Father for relief for my pain. . . . I saw a poor woman, barefoot, told to "Go to Hell and be glad for it" for asking for a glass of milk at a dairyman's wagon; she had in her arms a baby with its legs broken. I gave her a dollar and walked with her to the hospital. . . .I was pressed into service by an officer, who made me help to strike tents in front of the St. Francis Hotel, when the order was issued to dynamite all buildings in the vicinity to save the hotel. I like him, and hope to meet him again. When he saw I was hurt, which I had not told him, not yet having been bandaged, he took me to his own tent and gave me water and brandy and a clean handkerchief."

The earthquake and the firestorms killed estimated 3.000 to 4.000 people, destroyed 28.000 buildings and the infrastructure of the entire city - but in a surprisingly rush people begun planning and reconstruction work on their homes and life, three year later most of San Francisco was rebuild.

Seismology was still a young scientific discipline at the time of the earthquake in San Francisco, in part as a result of the lack of appropriate equipment like sensible tools to measure the tremors of earth - worldwide there were only 96 seismographs operating, none of these in California. In the aftermath of the disaster, only three days later, the Governor of California announced the formation of the State Earthquake Investigation Commission led by geologist Andrew C. Lawson of the University of California.
The commission concentrated their work on the San Andreas Rift, a local straight valley until them considered of minor interest and mapped only in short sections. For two years Lawson and his team followed the rift along ponds and streams and up and down poison oak-covered hills on foot and horseback, they recognized that the rift followed almost the entire coastline of California for more than 1.000 kilometres. During the April 18. earthquake nearly 480 kilometres of the Earth's surface along the today notorious known San Andreas fault line had ruptured displacing the ground horizontally instead of vertically, as geologists had previously believed to be the source of earthquakes.
The commission will locate the epicentre of the earthquake at the place of the greatest observed displacing on land - however today the epicentre is believed to be situated below the Pacific Ocean, in accordance to the seismic waves coming from the sea as observed by the first eyewitnesses.
Nevertheless this finding led team member Henry Fielding Reid, a geology professor at Johns Hopkins University in Maryland, to propose a new theory regarding the origin of earthquakes. Later dubbed the "theory of elastic rebound" Reid's hypothesis was to have a revolutionary impact on the young field of seismology.

Bibliography:

MORRIS, C. (2006): The San Francisco Calamity by Earthquake and Fire. Librivox
SLAVICEK, L.C. (2008): The San Francisco Earthquake and Fire of 1906. Great Historic Disasters. Chelsea House Publishers: 128
STARR, J.D. (1907): The California Earthquake of 1906. A.M. Robertson, San Francisco

Online Resources:

USGS (2009): The Great 1906 San Francisco Earthquake. (Accessed on 17.04.2011)

Geological risks and human society

"Civilization exists by geological consent, subject to change without notice."
Will Durant (1885 - 1981) American writer, historian, and philosopher

Fig.1. Woodcut of the "terrible and great" water-flood in the year 1651 of the German river Rhine.

Earthquakes and volcanic eruptions are part of the activity of earth and not controllable or alarming as natural events; however as these events affect human infrastructure they became natural disasters.
Human population today tends to be concentrated in cities, in 1950 just 30% of the world's population lived in urban areas, today already it is 50% and until 2025 it will likely increase to 60%.

Unfortunately many urbanized areas are concentrated in regions with strong seismic or volcanic activity - cities and harbours developed along coasts where oceanic plates move under continental plates. Islands and regions with volcanic soils are very fertile and attract people. In contrast seismically stabile regions like Siberia or the interior of Australia are strongly weathered and the soils depleted of nutrients.
Considering the distribution of earthquakes and the density of population the most dangerous countries are located around the Pacific Ocean (the notorious ring of fire) like Indonesia, Japan, China, North to Central America and the Andes, also countries in the Near East and around the Mediterranean Sea are at risk.

Fig.2. Simplified map with earthquake events, volcanoes and larger cities, modified after U.S.G.S. 2005.

Fig.3. "...the resulting map gives each person living on earth the same amount of space while also preserving the geographical reference. This map allows to understand the earthquake intensity in relation to today’s population distribution, and thus gives an idea of where most people are of risk related to seismic activity.", Global Earthquake Intensity map after Benjamin Hennig 2011.

The increment and concentration of humans and infrastructure in narrow spaces increases the risk of and the impact from natural hazards like floods, earthquakes and volcanic eruptions, even small disasters can have great effects. Main problems are the to high grow rates, overcrowding population, no adequate infrastructures and development planes, limited space, mismanagement and corruption, all these factors increase the vulnerabilities of large cities and their inhabitants to local events.
Also modern technology and industry tends to be concentrate in single spots, however at the same time globalization tends to interconnect economies worldwide - a local catastrophe can so have worldwide economics percussions.
Living in highly technological cities also poses the danger that people loss contact and so awareness to natural hazards. In slightly modified or rural areas traces of past catastrophes can be observed, like landslide scars or deposits of rock fall or debris flows, in urbanized areas these traces tend to be smoothed or cancelled to build new infrastructures.
Defence or protection constructions tend also to smooth the temporal occurrence of natural hazards, most of these measures are build to prevent short term events of lower magnitude, producing the false impression that floods or mass wasting processes in general are extraordinary and rare events. People behind the protection wall tend to be less vigilant or reduce private mitigation measures. When then an event is large enough to overcome the protection barriers, the results tend to be even more disastrous.

Even if natural disasters are not controllable, what is manageable is the response of single individuals and society to such a catastrophe, interestingly this response is strongly influenced by the former experience of catastrophes and the form of government in the afflicted region.

- The Netherlands, with large areas located on sea level, had to deal in historic times with floods and storms coming from the North Sea. In the last centuries with an ambitious project and kilometres of dams' additional large land areas lying below sea level were gained from the sea. The struggle against natural disasters is fought with technology and considered a task for the entire society.

- In the U.S. the answers to the inundation caused by hurricane Katrina in New Orleans were mixed between government actions and individual interests. Authorities reacted unprepared in a first moment and help was organized late, however there were strong efforts by local groups or individuals. When the government intervened, many homeowners refused to abandon their properties and tried to deal with the catastrophe independent.

- In strongly organized and centralized governments, like Cuba or China, ordered evacuations are followed mostly without opposition.

The wealth of a society plays also an important role in the results of a catastrophe. In the Indian city of Delhi the poorest people are concentrated at the city limits or in the areas of less interest for city planners, areas however in danger to become inundated, as happened in summer 2010 when the river Yamuna flooded the slums.

After many catastrophes follows the "blame game". Humans tend to connect an effect to a cause, during medieval times it was god or the devil, today it is mostly the behaviour of politics, economics or society. Often in the apparent rational blame a certain supernatural believe still persists. Many natural disasters are comprehended as a sort of revenge by misbehaviour of western civilization against nature, like regulation of rivers or overexploitation of natural resources.

Bibliography:

CHESTER, D.K.; DEGG, M.; DUNCAN, A.M. & GUEST, J.E. (2001): The increasing exposure of cities to the effects of volcanic eruptions: a global survey. Environmental Hazards 2: 89-103

Online Resources:

SWAAF, K.F. de (20.03.2011): Von Ruhe bis Hysterie - So geht die Welt mit Katastrophen um. (Accessed 27.03.2011)

27 March, 1964: The Alaska Earthquake

“One day earthquake and thunder decided to explore the world, but doing so they reached only a desolate and dry plateau. Earthquake noted that the land was located much too high in the sky for humans “They will have no food, if there is no place for the creatures of the sea to live in!” Earthquake begun to shake, stronger and stronger, until the earth finally collapsed and the sea inundated the land. Earthquake was satisfied “From here, they will obtain what they need to live, where prairie has become water…. This is what brings to the people life.” Thunder acknowledged what earthquake had done “It is true. So they will survive!” and so they went further north and together they lowered the land and created the western coast.”
The creation of the world according to a legend of the Yurok people (Cascade Range)

In the late afternoon of March 27, 1964 Alaska was shaken for five minutes by one of the strongest earthquakes ever to be recorded in modern times, with a magnitude of 8.3 – 9.2 after Richter (the earthquake was so strong that no seismometer in the affected area recorded it correctly).
The earthquake displaced almost the entire southern coast of Alaska along the Prince William Sound, some areas were raised by 9 meters (30 feet) above the sea level, other dropped below sea level and became inundated later by the sea (maybe the Yurok myth is based on the observation of such a similar environmental change after an earthquake in prehistoric times along the western coast of the U.S.).

The earthquake caused heavy damage on 75% of buildings and infrastructure in the affected area, most in the city of Anchorage, 131 people were killed.
Large fissures opened in the ground when the groundwater liquefied the soil and more than 2.000 landslides and avalanches occurred across south-central Alaska. Buildings in Seattle (Washington) begun to swing by the approaching seismic wave and the ground was measurable deformed even in Florida.

Fig.1. Aerial photographs of destructive landslides and damage in Anchorage, Photo by A. Grantz / image in public domain from the U.S.G.S. Photographic Library.

In some lakes in Alaska the movement of the water catapulted chunks of ice onto the land, causing damage on the surrounding trees up to 9 meters (30 feet) above ground. Unusual water movements, attributed cautiously to the earthquake, were observed in South Dakota and apparently even in Puerto Rico and Australia.
Most remarkable was the generated tsunami, waves higher than usual were observed even along the Japanese coast. The seaport of Valdez was destroyed by a 30 meter high tsunami, 32 people died there. For hours after the earthquake the sea was tumultuous and in the evening with the high tide the reflected waves of the first tsunami inundated the surviving area of the city of Valdez.
Six hours after the earthquake the tsunami reached the coasts of Vancouver Island, one hour later the coast of Oregon and the wave caused damage even in Crescent City and Los Angeles (California). 

Many of these phenomena were studied for the very first time by scientists – only two hours after the earthquake the first geologists arrived to Anchorage.

Fig.2. Alaska Earthquake March 27, 1964. Rockslide avalanche on Sherman Glacier. The source was from the area marked by the fresh scar on Shattered Peak (top center image). The debris displays flowlines and terminal digitate lobes. No marginal dust layer is present. The steep margin, about 20 meters above the clear ice, is due to more rapid melting of the exposed glacier than the ice protected by the debris. Photo by A. Post, August 25, 1965 / Geological Survey.

Bibliography:

Committee on the Alaska Earthquake of the Division of Earth Sciences National Research Council (1968): The Great Alaska Earthquake of 1964. National Academy of Sciences, Washington: 473
GATES, A.E. & RITCHIE, D. (2007): Encyclopedia of earthquakes and Volcanoes. Facts on file science library. 3th ed. New York: 346
WALKER, B. (1982): Earthquake. Planet Earth. Time Life Books: 154

Online Resources:

GATES (2007): U.S.G.S. (21.10.2009): Historic Earthquakes - Prince William Sound, Alaska 1964.

Tsunamis in the geological record

Tsunami deposits are well documented in the Holocene and the Pleistocene, in part by the good accessibility in outcrops to rocks of these epochs or when historic records help to identify areas subjected to tsunamis.

Modern databases list more than 2.000 tsunami events for the lat 4.000 years, most of them recorded in documents and chronologies and others inferred by their geological evidence.
It seems also possible that tsunamis in historic times (after 1700) have found place in myths and oral tradition of the local Indian tribes of the Cascade Range. Based on these stories geologists tried to establish a chronology of events, backed by geological evidence.

Fig.1. Temporal distribution of 2341 tsunami events listed in the database of the National Geophysical Data Center, USA. The database contains the events of the past 4000 years until 2001 AD, from SCHEFFERS & KELLETAT 2003.

However such a database has to be very incomplete, tsunami without greater damage or loss of life are likely to be underrepresented in historic documents, tsunamis with disastrous effects can in contrary became overemphasized and tsunamis occurring in uninhabited regions will not even be noted by humans. With the age of colonization and exploration the known and inhabited zones grow rapidly, and so also the record of large, destructive tsunamis apparently experienced a mayor increase.
However it can be assumed that the actual number, frequency and power of tsunami in such a compilation are still inaccurate and probably underestimated in the past and emphasized in the present the occurrence of strong tsunamis.
In the geologic record examples of ancient tsunamis are however quite rare. The coastal environment, like flood plains or the estuary of a river, are subject to continues reworking, erosion and deposition, a single event like a tsunami can got destroyed even before it's deposits or traces can became fossilized.
Also in such a complex environment single events tend to became homogenized and amalgamated with the "background" sedimentation, like deposits of the tides or storm events.

In theory a tsunami can produce various geologic evidences in four phases: it can both deposit sediments and erode them during generation, propagation, run up on land and backwash current. The sedimentologic record of the run up by a tsunami on land is well described by this post at "Trough The Sandglass", especially sand layers, and it´s environmental effects at "paleoseismicity" - however tsunamis can transport and deposits giant boulders (like reef debris thrown on land), these boulders are unlikely to be reworked by normal processes of a coastal environment and have a great potential to become fossilized.
Liquefaction phenomena like sand dikes and intrusion during the earthquake are preserved in the sediments underlying the soil and tsunami deposits.

Fig.2.Worldwide published distribution of coastal boulders thrown on land as evidence for tsunamis. Historical tsunami and storm wave boulders were defined here as those purporting to show clear depositional evidence based on historical descriptions, direct observations, and analyses of aerial photographs during the historical age (from GOTO et al.2010).

There is also indirect biological evidence to infer the occurrence of a tsunami.

A strong earthquake can cause a displacement of great parts of a coastal area and the land can become inundated by the sea. The salt water soon will kill trees and plants growing on this land. Because dead trees will survive for quite a while as "Ghost forests" the tree stumps can became buried in the sediments of the tidal flat. After the displacement the land can rise upward by the continuing tectonic movements and again became dry.
These changes can be observed in the stratigraphic succession: layers of peat or soil with tree stumps will change suddenly to sand and silt layers deposited by the tsunami and the tides. The plant remains can be dated by the radiocarbon method and are used to produce a chronology of the changes.

Fig.3. Summer in the ghost forest in Alaska and the remains of the town of Portage after the earthquake of 1964 and in the year 1998. In the background of the old photo spruce trees are dying and the high tide covers recently subsided land. In the modern photo still few trunks are standing and shrubs cover the land rebuilt by tidal silt (after BOLT 1995 and ATWATER et al. 2005).
The 1964 Alaska earthquake was a megathrust earthquake that began at 5:36 P.M. on Good Friday, March 27,.1964. Across south-central Alaska, ground fissures, collapsing buildings, and tsunamis resulting from the earthquake caused about 131 deaths.

The remains of the trees provide even a more accurate chronology: The sudden occurrence of the event is proved by the tree rings, a gradual subsidence of the land would produce a different pattern in the rings that the sudden interruption often observed in cedar trees along the North American coast.

Bibliography:

ATWATER, B.F.; SATOKO, M.-R.; KENJI, S.; YOSHINOBU, T.; KAZUE, U. YAMAGUCHI, D.K. (2005): The Orphan Tsunami of 1700 Japanese Clues to a Parent Earthquake in North America. U.S.G.S. - University of Washington Press: 144
BOLT, B.A. (1995): Erdbeben - Schlüssel zur Geodynamik. Spektrum Akademischer Verlag, Berlin: 219
DAWSON, A.G. & STEWART, I. (2007): Tsunami deposits in the geological record. Sedimentary Geology 200: 166-183
GOTO, K.; KAWANA, T. & INAMURA, F. (2010): Historical and geological evidence of boulders deposited by tsunamis, southern Ryukyu Islands, Japan. Earth-Science Reviews 102: 77-99
SCHEFFERS, A. & KELLETAT, D. (2003): Sedimentologic and geomorphologic tsunami imprints worldwide-a review. Earth-Science Reviews 63: 83-92

Earthquake - myths: North America

"It is not good that these stories are forgotten. Friends, you are telling them from mouth to ear, and when your old men die they will be forgotten. It is good that you should have a box in which your laws and your stories are kept. My friend, George Hunt, will show you a box in which some of your stories will be kept. It is a book that I have written on what I saw and heard when I was with you two years ago. It is a good book, for in it are your laws and your stories. Now they will not be forgotten."

American Anthropologists Franz Uri Boaz in a letter to the Kwakiutl Indians of British Columbia, April 1897

Oral tradition and legends all over the world maybe represent the first efforts to record and explain geological phenomena. In all cultures it was tried to explain why things happen as they happened, catastrophic events were no exception and during centuries a rich collection of stories were told and retold.
The Japanese Namazu-myth is one of the most popular and remembers the tragic connection between society and geology in the form of earthquakes, but many other myths on the various continents try to explain why earthquakes occur and kill people.
However myths address lesser the question how something happens (as for example modern science) than why it happens - humans tend to interpret phenomena in relation to a presumed end-cause, if for example a supernatural forces causes an earthquake it is often to establish the lost equilibrium of creation - it is not important how it is done, but the results in the supernatural world, even if some minor traces remain back in the "real world."
Also the apparent connection between ancient myths and modern concepts is often biased by interpretation, if a certain term is translated from an ancient language and modern terms used, like "earthquake", we can not be sure to exactly "catch" the quintessence or meaning intended by the original author - so the following selection of mythical stories and creatures is surely biased by my interpretation or "earth trembles" and other "earthquake effects".
Despite these considerations, myths can be wonderful stories worth to be at least remembered:

The Duwamish people, natives of the Cascade Range, tell of the terrible "A´yahos", spirits with the body of a serpent and the antlers and forelegs of a deer. Old folks warn to look directly to an A´yahos because it could shake the ground or turn people to stone. The Quileute people know a similar entity, the "T´abale", a vicious guardian spirit on the north-western Washington coast. The Indigenous group of the Kwakwaka'wakw tell stories about the two-headed "Sisutl".

The bay of Lituya is a remote place situated in Alaska. It is a narrow, only 2 kilometres broad, but 11 long bay open to the Pacific Ocean. The native Tlingit Indians tell that in a cavern, deep in the underground, lives a demon, similar in appearance to a great toad or frog. If someone dares to disturb the tranquillity of the bay the demon will rip apart the sea and shake the earth and catch the intruder and transmute him into a bear.

Many catastrophes however were not the acts of demons, but an essential part of creation - these events were necessary to form a world habitable by us humans.

The Yurok Indians, once native in the Cascade Range, tell about the creation of the world by "earthquake" and "thunder":

"One day earthquake and thunder decided to venture south, but doing so they reached only a desolate and thirsty plateau. Earthquake saw that the land was located much to high in the sky for humans "They will have no food, if there is no place for the creatures of the sea to live in!" Earthquake begun to shake, stronger and stronger, until the earth finally collapsed and the sea inundated the land. Earthquake was satisfied "From here, they will obtain what they need to live, where prairie has become water…. This is what brings people to live." Thunder acknowledged what earthquake had done "It is true. So they will survive!" and so they went further north and together they lowered the land and created the sea."

Unfortunately gods often were moody and their fights were carried out on or below the surface of the earth.
The Klamath people of Oregon tell of the time when the chief of Above World - called Skell- and the chief of Below World - called Llao- decided to settle the dispute which of them was stronger. For many days the fight raged over the land, the two adversaries' hurled rocks and flames at each other and soon darkness covered the land.
To better see his adversary Llao decided to climb on the highest mountain he could find - Mount Mazama - but as soon he reached the peak the mountain collapsed with terrible vibrations and thunders under him and hurled him back into his underworld domain. The large hole that was created then filled up and became known as Crater Lake.

Many tribes from Vancouver Island until northern Washington know of the fight of gods in the guise of animals. He is remembered under many names, the Lakota call him "Waki-ya", the "sacred winged being", the Nuu-chah-nulth called him "Kw-Uhnx-Wa" and today we call him the powerful "Thunderbird".
Thunderbird was easy to enrage and it was better to avoid him when he flew above the sky to cause the thunder of the storm, but deep inside he was a friendly and helpfully spirit.
One day a monstrous whale begun to kill all the animals in the sea depriving the Quileute tribe in Washington of meat and oil. Thunderbird saw from its home high in the mountains that the people were starving and decided to interfere. Thunderbird plunged into the ocean and a terrible battle arouse between him and Whale. The ocean receded and rose again, many canoes were flung by waves into trees and many people were killed. Thunderbird eventually succeeded in lifting Whale out of the ocean, carrying it high into the air and then dropping it onto the land.
The earth trembled under the ongoing battle, finally Thunderbird succeeded with the help of wolf and serpent to throw Whale back into the sea and dragging him to the bottom of the sea.
In other versions of the story it is thunderbird starting the fight by attacking whale, which supports the earth on his back, and droving his claws deep into his flesh. Whale in his struggle shakes the land until he finally drags thunderbird to the bottom of the sea.

References:

LUDWIN, R.S. & SMITS, G.J. (2007): Folklore and earthquakes: Native American oral traditions from Cascadia compared with written traditions from Japan. In Piccardi, L. & Masse, W.B: (eds): Myth and Geology. Geological Society, London, Special Publications, 273: 67-94
VITALIANO, D.B. (2007): Geomythology: geological origins of myths and legends. In Piccardi, L. & Masse, W.B: (eds): Myth and Geology. Geological Society, London, Special Publications, 273: 1-7