Earthquakes

A shaking of the Earth’s crust caused by a release of energy and results from the movement of the lithospheric plates

Most destructive of the natural disasters, affects largest area

Causes of Earthquakes Eruption of volcanoes underground caverns collapsing meteorites Stress builds between lithospheric

plates-stress > friction forces, plates move- Earthquake- plates return to same shape, but different locations Elastic-rebound theory

Depth of Earthquakes

Depends on the type of boundary

Spreading centers, sliding boundary shallow quakes (30 km deep)

Subduction, deep quakes (700 km)

Focus - point on fault plane where first movement occurs

Epicenter - point on surface directly above focus

Earthquake WavesThree kinds of wave motion

1. Compressional-back and forth wave motion causes rock material to be squeezed and stretched

P-wave)Primary waves 1st to arrive at seismograph station can travel through any material

2)Shear waves causes rock material to move side to side or right angles to direction the wave is traveling

S waves or secondary waves can not travel through liquids or gases

P and S waves are body waves, they travel thru body of Earth

L waves = P & S waves combine at surface called surface waves

Speed of Waves

Depends on type and nature of rock

Velocity of waves is greatest when rock is rigid and dense

P waves travel twice as fast as S waves in any material

L waves travel slower than both P and S waves

Seismographs The instrument that detects and

records earthquake waves Several types record different

motions Drum moves, not pen (Inertia) First recorded wave is P wave Larger the deflection, larger quake

•Record sheet is called seismogram

Finding Distance and Location

P wave arrives first, then S wave

Greater the difference in arrival time the further away the earthquake

Use time-travel graph to find distance from epicenter~ 1 station

Need 3 stations to determine location of epicenter~~ triangulation

Richter Scale of Magnitude

Each magnitude number represents an earthquake with 32 times more energy released

Difference of two,

1000 X stronger

Amplitude of earthquake wave is 10 X greater per magnitude

Magnitude (Richter Scale) What are the Magnitude classes?

Great = M > 8Major = 7 < M < 7.9Strong = 6 < M < 6.9Moderate = 5 < M < 5.9Light = 4 < M < 4.9Minor = 3 < M < 3.9

Seismic Moment tells total energy 1}Takes into account amount of

movement along fault plane

2} size of fault plane

1906 San Francisco and 1964 Alaskan Earthquakes both had magnitudes of 8.3 on Richter

SF=7.9 and AK=9.2 seismic moment

12 levels of Modified Mercalli Intensity.

I. Not felt except by a very few under especially favorable conditions.

II. Felt only by a few persons at rest, especially on upper floors of buildings.

III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.

IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.

X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.

XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.

XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.

Earthquake DamageGround shaking ~ causes Earth to vibrate and buildings to shake up and down and sideways.

Foundation failure ~ results from ground shake: causes soil to settle and liquefy

Earthquake Risk & PredictionForecasts:

1) When, 2) Where, 3) Magnitude

Seismic Gap Method

Fore shocks, elevation increase, tilting, decrease in electrical resistance, radon in wells increase, P waves slow, porosity less, premonition of animals

Earth’s Interior and WavesInformation about Earth’s interior

has come from seismic waves

Change in velocity at 2900 km depth shows where the mantle meets core

Outer core liquid, S wave velocity 0

Boundary of crust/mantle named (Moho) Mohorovicic Discontinuity

32 km below continents, 8 km /ocean

Shadow Zone Waves sent in all directions from

focus of earthquake, but not all seismograph stations receive info

Broad belt on opposite side of Earth from quake do not receive P or S waves because of the outer core being liquid

Area called shadow zone

Examples of Earthquakes

Alaska 1964-

caused by subduction

California,

continuous sliding boundary ( San Andreas Fault)

Missouri-

zones of weakness in craton a midplate earthquake

Loma Prieta DATE: Oct. 17, 1989 TIME: 5:04 PM MAGNITUDE: 7.1DURATION: 15 secondsDEATHS: 62INJURIES: 3,757PROPERTY DAMAGE: >$6 BillionCOMMENTS: rupture of 40 km fault stretch (25 mi. [40 km] segment of San Andreas fault SW of San Jose slipped ~ 7 ft]; SF Bay Bridge unusable for 1 month; 18,306 homes damaged; 2,575 business damaged; 12,053 people displaced

San Francisco 1906 DATE: April 18, 1906TIME: 5:12 amMAGNITUDE: 8.25DURATION: 40 secondsDEATHS: 700-2,500 people (debated)COMMENTS: 400 km fault segment released; San Andreas fault slipped as much as 15 ft along 270 mi. (434 km) segment from south of San Jose to northwestward to Cape Mendocino

Largest Earthquake in North Carolina

Near Waynesville, North Carolina 1916 02 21 23:39 UTC, 5.20Mfa, MM VII

Tops of chimneys were thrown to the ground; windowpanes were broken in many houses; and people rushed into the streets at Waynesville. At Sevierville, Tennessee about 70 kilometers northwest of Waynesville, bricks were shaken from chimneys. In Wear's Cove, about 16 kilometers southwest of Sevierville, the flow of water in springs increased and in places water became muddy. Minor damage was reported in western Tennessee at Athens, Knoxville, Maryville, Morristown, and Newport, Tennessee; at Tryon, North Carolina; and at Bristol, Virginia. Also reported felt in Alabama, Georgia, Kentucky, South Carolina, and West Virginia.

10 Largest Earthquakes in Contiguous US1.) New Madrid, Missouri 1812 02 07 7.9

2.) Fort Tejon, California 1857 01 09 7.9

3.) Owens Valley, California 1872 03 26 7.8

4.) Imperial Valley, California 1892 02 24 7.8

5.) New Madrid, Missouri 1811 12 16 7.7

6.) San Francisco, California 1906 04 18 7.7

7.) Pleasant Valley, Nevada 1915 10 03 7.7

8.) New Madrid, Missouri 1812 01 23 7.6

9.) Landers, California 1992 06 28 7.6 Ms

10.) Kern County, California 1952 07 21 7.5

On the basis of the large area of damage (600,000 square kilometers), the widespread area of perceptibility (5,000,000 square kilometers), and the complex physiographic changes that occurred, the Mississippi River valley earthquakes of 1811-1812 rank as some of the largest in the United States since its settlement by Europeans. The area of strong shaking associated with these shocks is two to three times larger than that of the 1964 Alaska earthquake and 10 times larger than that of the 1906 San Francisco earthquake.

The first and second earthquakes occurred in Arkansas (December 16, 1811 - two shocks - Mfa 7.2, MSn 8.5 and Mfa 7.0, MSn 8.0) and the third and fourth in Missouri (January 23, 1812, Mfa 7.1, MSn 8.4; and February 7, 1812, Mfa 7.4, MSn 8.8). Otto Nuttli, however, has postulated another strong earthquake in Arkansas on December 16 at 18:00 UTC (MSn 8.0). This would make a total of five earthquakes of magnitude MSn 8.0 or higher occurring in the period December 16, 1811 through February 7, 1812.

10 Largest Earthquakes in US1.) Prince William Sound, Alaska 1964 03 28 9.2

2.) Andreanof Islands, Alaska 1957 03 09 8.8

3.) Rat Islands, Alaska 1965 02 04 8.7

4.) East of Shumagin Islands, Alaska 1938 11 10 8.3

5.) Lituya Bay, Alaska 1958 07 10 8.3

6.) Yakutat Bay, Alaska 1899 09 10 8.2

7.) Near Cape Yakataga, Alaska 1899 09 04 8.2

8.) Andreanof Islands, Alaska 1986 05 07 8.0

9.) New Madrid, Missouri 1812 02 07 7.9

10.) Fort Tejon, California 1857 01 09 7.9

Trees up to 24 inches in diameter and between 88 and 101 feet above sea level were broken and splintered by the surge wave generated by an underwater landslide in Port Valdez, Prince William Sound.

10 Largest Earthquakes in the World Since 1900

1.) Chile 05/22/1960 9.5 Mw 38.2 S 72.6 W *8.3 Richter

2.) Alaska 03/28/1964 9.2 Mw 61.1 N 147.5 W *8.3 R

3.) Russia 11/04/1952 9.0 Mw 52.75 N 159.5 E

4.) Ecuador 01/31/1906 8.8 Mw 1.0 N 81.5 W

5.) Alaska 03/09/1957 8.8 Mw 51.3 N 175.8 W

6.) Kuril Islands 11/06/1958 8.7 Mw 44.4 N 148.6 E

7.) Alaska 02/04/1965 8.7 Mw 51.3 N 178.6 E

8.) India 08/15/1950 8.6 Mw 28.5 N 96.5 E

9.) Argentina 11/11/1922 8.5 Mw 28.5 S 70.0 W

10.) Indonesia 02/01/1938 8.5 Mw 5.25 S 130.5 E

Chile 1960 May 22 19:11:14 UTC, 9.5 Mw

More than 2,000 killed, 3,000 injured, 2,000,000 homeless, and $550 million damage in southern Chile; tsunami caused 61 deaths, $75 million damage in Hawaii; 138 deaths and $50 million damage in Japan; 32 dead and missing in the Philippines; and $500,000 damage to the west coast of the United States.

Tangshan, China-240,000 dead-2,000 in dormitory-7/27/76

Kobe