Earthquakes

Causes for Crustal movement:

A. Strain – The deformation of

materials in response to stress.

B. Stress – The total force acting on crustal rocks per unit of area.

B. Elastic (temporary breaking or bending)

C. Plastic (permanently breaking or bending of the surface)

• Tensional Stress- pulls outward (extensional stress)

• Compressional Stress- pushes inward

• Shearing- pulls in two opposite directions

Syncline “sinks”

Anticline folds up like a capital “A”

Folds–(elastic) There are 2 types of bends that can occurs in Earth’s crust.

Faults (plastic deformation) – breaks in the Earth’s crust along which Earth’s crust moves.

Hanging wall – The side of the fault which is thicker at the top (you can “hang” from it)

Foot wall – The side of the fault which is thicker at the bottom (you can “walk” up it)

Faults produce 2 sides (walls):

Normal FaultNormal Fault – Tension pulls rock apart, forcing the footwall up and the hanging wall down.

Normal Fault Animation

Normal Fault

Stress = Tension

Left: Fault scarp near Hebgen Lake, Montana, after the magnitude 7.1 earthquake of August 18, 1959, shows a displacement of 5.5 to 6.0 m.

Right: This section of the normal fault scarp was produced by the earthquake

of October 28, 1983, at Borah Peak, Idaho.

Left: Dixie Valley-Fairview Peaks, Nevada earthquakeDecember 16, 1954

Normal Fault Examples

Reverse Fault

Reverse Fault – Compression causes the hanging wall to move up and the footwall to move down.

Reverse Fault Animation

Reverse Fault

Stress = Compression

Reverse Fault Example – Collision ZonesBam, Iran 2003

Earthquakes in Iran and neighboring regions (e.g., Turkey and Afghanistan) are closely connected to their position within the active Alpine-Himalayan belt near the convergence of the Arabian and Eurasian plate.

Map showing the Alpine-Himalayan Belt.

Below: Before and after pictures of the 2,000 yr. old citadel in the city of Bam, the largest mud-

brick structure in the world.

The Mw 6.5 Bam Earthquake destroyed nearly 80% of the adobe buildings killing more than 26,000 people.

Thrust Faults - Reverse Faults

• Reverse faults result from compressional stresses along convergent boundaries.

• The hanging wall block has moved up relative to the footwall block.

• A Thrust Fault is a special case of a reverse fault where the dip of the fault is less than 15o

• It is a reverse fault at a very low angle.

• There are two types of converging plate boundaries.1.Subduction boundaries 2.Collision boundaries

Strike-slip FaultStrike-Slip Fault – Shearing forces two parts of Earth’s crust past each other with NO vertical movement.

Strike-Slip Animation

Strike-Slip Fault

Stress = Shearing

Strike-Slip Faults - Transform Faults• Strike-slip faults result from shear stresses acting on the

lithosphere along transform boundaries.

• Horizontal motion can be right lateral or left lateral.

• Earthquakes along these boundaries tend to be shallow focus with depths usually less than about 100 km. Richter magnitudes can be large.

Earthquakes DefinedEarthquakes are vibrations of the earth caused by the rupture and sudden movement of rocks that have been strained (deformed) beyond their elastic limit. The forces that cause deformation and the build-up of strain energy in the rock are referred to as stresses.

Earthquakes occur along faults.

• Faults are fractures in the lithosphere where regions of rock move past each other (displaced).

• The focus is the point on the fault where rupture occurs and the location from which seismic waves are released.

• The epicenter is the point on the earth’s surface directly above the focus.

• When the fault ruptures, waves of energy called seismic waves spread out in all directions.

Inside Earthquakes Video

Footage for California Earthquake in 1989

Part of Documentary showing footage from 2011 Earthquake in Japan

Earthquake Seismic Waves

Body waves travel through the interior (body) of the earth as they leave the focus. They include P-waves and S-waves.

• Primary (P) -Travel twice as fast as S-Waves, are compressional Movement: rocks are squeezed and pushed in the same direction as the wave moves.

-Move similar to a slinky that is stretched and then released.

• Secondary (S)-Travel half as fast as P-Waves, rolling Movement: rocks shifted up and down perpendicular to the direction of the wave.

-Move similar to a rope that is being shaken up and down.

Surface waves travel parallel to the earth’s surface. They are the slowest and most damaging because they cause the most ground movement. They include Love and Rayleigh Waves.

• When combined, these waves move the ground up and down and side to side simultaneously.

• -They cause the most damage because the create the most ground movement and take the longest time to pass an area.

Love Waves - complex, horizontal motion

Rayleigh Waves - Rolling or elliptical motion.

Interior seismic waves – These waves travel through the inner layers of Earth.

Primary Waves

Secondary Waves

COMPARE P WAVES AND S WAVES

-Travel half as fast as P-Waves.

-Rolling Movement: rocks shifted up and down perpendicular to the direction of the wave.

-Move similar to a rope that is being shaken up and down.

How do we measure earthquakes?

Richter Scale Mercalli Scale

-Created by Charles Richter in 1934.-This scale measures earthquakes based on the largest seismic wave recorded during a quake.

-The scale is from 0-10. Every whole number up on the scale represents an increase in energy of ten times more.

-The original scale used to measure quakes. Created in 1902 by Giuseppe Mercalli.

-Considered less accurate, because it uses eyewitness observations of damage to estimate the intensity of the quake.

MERCALLI SCALE

**This is the most accurate scale used today**

Moment Magnitude Scale

-Introduced in 1979.

-Measures earthquake strength based on the amount of energy released by calculating size of the fault, amount of movement, and type of rock (stiffness).

-The moment magnitude scale is preferred over the Richter scale by seismologists because it is more accurate.

-When hearing about an earthquake on the news, this is typically the final, most accurate magnitude given.

Earthquake Richter Scale Moment Magnitude

New Madrid, MO, 1812 8.7 8.1

San Francisco, CA 1906 8.3 7.7

Prince William, AK 1964 8.4 9.2

Northridge, CA,1994 6.4 6.7

Earthquake Depth Shallow earthquakes

cause the most

damage.

Intermediate earthquakes

cause moderate damage

Deep earthquakes

cause the least

damage.

LiquefactionLiquefaction is a quicksand like condition that occurs in water-saturated soil and rock. The shaking of earthquake waves causes the soil or rock to turn into a weak, fluid-like mass. Structures built on areas that liquefy may fall over or sink.

Above: Buildings in Niigata, Japan, fell over when the sediments below them liquefied during the 1964 earthquake

The figure below shows how liquefaction can occur. Shaking of water-saturated soils causes the particles to settle, driving the water out from between the particles and forcing it upward, thus liquefying the areas above.

LandslidesVibration of water saturated sediment can force water into pore spaces between sediment grains reducing friction and permitting the mass to slide down slope.

Turnnagin Heights,Alaska,1964- This landslide occurred during the massive recording breaking earthquake

This massive landslide near Oso, Washington, in March, 2014, killed 43 people and was one of the most deadly in U.S. history. This occurred to heavy rains over saturated the soil the gravity pulled the mountain downward on top of this small town.

Largest Earthquake in US HistoryAlaska, 1964

Alaska - March 27, 1964

-This is the most powerful U.S. earthquake in recorded history.

-It registered as a 9.2 on the Richter scale.

-The rumbling lasted nearly 5 minutes.

-Ground fissures, collapsing buildings, and tsunami killed over 130 people

-The Pacific Ocean Tsunami Center was created shortly after this earthquake and has predicted several tsunamis, saving lives.

San Francisco, California – 1906

San Francisco, California – 1906 (7.7 on Richter)

-Significant earthquake in that it was one of the first instances where scientists were able to record information on seismic waves.

-Caused approximately $400,000,000 of damage (at the time)

-Several eye-witness accounts refer to the movement of the roads to be similar to the undulation of waves in the ocean.

-Fires raged on for days, and S.F. had to be rebuilt.

Full Documentary on Earthquakes

Indian Ocean – December 26, 2004

9.2/9.3 magnitude earthquake, making it one of the most powerful ever recorded on Earth.

-The infamous tsunami that ensued killed over 200,000 to 250 people in more than 11 countries, most bodies were never found..

-Released an amount of energy 1502 times more powerful than the Hiroshima atomic bomb.

The Los Angeles Times reported: “Miles beneath the waters of the Indian Ocean, a massive piece of the Earth’s crust had heaved, buckled and shifted. Along a fracture zone hundreds of miles long, it moved, releasing pent-up energy equivalent to the power of more than 1,000 atomic bombs. The waters above reared up and crashed down, creating a wave that was now racing across the ocean at 500 mph…The records of history and evidence encoded in coral reefs show that tsunamis have hit the Indian Ocean seldom but with great force.”

The Full PBS Documentary on the 2004 Tsunami

Chile – May 22, 1960

The most powerful earthquake ever officially recorded at a magnitude of 9.5.

-The damage is estimated to be at over 3 billion dollars, and nearly 6,000 killed.

-Once the red slab that is “stuck” finally gives way, this is when the earthquake occurs. The recoil of the plate causes the energy to be released.

Haiti-20107.0 on 1/12/10Over a quarter of a million people were killed in this very shallow but rather low magnitude earthquake. Many of these deaths occurred because; it occurred in the countries capital, most of the community was poor living in poorly built structures, it occurred in the middle of the night while most were sleeping in their homes and their government literally abandoned them leaving more to die from treatable diseases and starvation.

• 7.1 magnitude earthqauke

• 52 aftershocks

• over 250,000 dead

• 1,800,000 homeless.

• Quake was created by a blind thrust fault with a very shallow quake and poor constructed homes lead to high deaths.

Cause of the earthquake. Haiti lies right on the boundary of the Caribbean and North American plates. There was slippage along a conservative plate boundary that runs through Haiti. On 12 January 2010, a magnitude 7 earthquake hit Haiti at 16:53 local time.

CNN Report on Haitian Earthquake

Chile (2/27/10)8.8 (MM)

• shook central Chile creating a tsunami.

• Lasted 3 minutes and was ranked as 8th largest in the world

• killed 802 people

BBC Reports on Earthquake in Chile 2010

Japan- 3/11/11 8.9 shallow quake created a 23-30 foot tsunami which spread over 1500 miles, around 11,000 dead at this time but numbers will increase, nuclear crisis still impacts the soils and water/ocean of Japan.

Japan is located on the eastern edge of the Eurasian Plate. The Pacific Plate, which is an oceanic plate, subducts (sinks under) the Eurasian Plate, which is a continental plate, to the east of Japan.

The process of subduction is not smooth. Friction causes the Pacific Plate to stick. Pressure builds and is released as an earthquake. News Report and Footage

from the Japanese Tsunami of 2011

The Guardian Magazine- Japanese Tsunami

Largest Quakes in History1.May 22, 1960, Chile (9.5) The world's most powerful earthquake left 4,485

people dead and injured and 2 million homeless and killed a further 170 people as the tsunami hit the coasts of Japan and the Philippines.

2.March 27, 1964, a magnitude 9.2 hit Prince Island Sound, Alaska. The earthquake caused landslides in Anchorage and raised parts of outlying islands by as much as 11 meters. The 67meter high tsunami killed another 128 people.

3.December 26, 2004, a magnitude 9.1 hit Sumatra, Indonesia. (The Tsunami of the Impossible) The deadliest tsunami ever spread to 14 countries killing 230,000 thousand people.

4. November 4, 1952 a magnitude 9.0 hit Kamchatka, Russia, known as the USSR. A volcanic peninsula was the epicenter but the tsunami hit Hawaii. No deaths occurred but it was 3000 miles from the epicenter.

Images from top ten worst earthquakes in history

TsunamiTsunami-

A tsunami is a series of great sea waves caused by an underwater earthquake, landslide, or volcanic eruption. More rarely, a tsunami can be generated by a giant meteor impact with the ocean.

• The first wave in a tsunami is not necessarily the most destructive. Tsunamis are not tidal waves that curl but rather a WALL of water that rapidly floods inward towards the land with tremendous speed and height.

•  The powerful shock wave of energy travels rapidly through the ocean as fast as a commercial jet but goes UNFELT in the ocean by fisherman.

• Once a tsunami reaches shallow water near the coast first, the ocean water disappears along the beach and recedes outwards towards the deep ocean.

• Then, it is slowed down, the series of waves catch-up to each other and builds UPWARD.

• The top of the wave moves faster than the bottom, causing the sea to rise dramatically.

Tsunami Formation animation

Independently made series of live video from 2004 Tsunami

CNN Footage and story on the 2004 Tsunami