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Mr. Litaker

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Charles Richter, inventor of the Richter Scale. (Image courtesy of

Caltech)

Seismology

Seismology is the study of earthquakes and the structure of the earth, by both naturally and artificially generated means.Developed in 1935 by Charles Richter in collaboration with Beno Gutenberg.

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Ring of FireThe "Ring of Fire", also called the Circum-Pacific belt, is the zone of earthquakes surrounding the Pacific Ocean--about 90% of the world's earthquakes occur there. The next most seismic region (5-6% of earthquakes) is the Alpide belt (extends from Mediterranean region, eastward through Turkey, Iran, and northern India.

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http://neic.usgs.gov/neis/eqlists/10maps_world.html

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An Earthquake is caused by sudden release of elastic energy stored in rocks.

Elastic deformation: Any changeof shape or size that disappearswhen the deforming forces areremoved.

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The Earth's surface is broken. Cracks in the Earth's crust known as faults can run for hundreds of kilometers. These faults are frequently the sites of major earthquakes as the tectonic plates that cover the surface of the Earth shift. Pictured above is San Andreas Fault in California, one of the longest and most active faults

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Parkfield

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http://earthquake.usgs.gov/eqinthenews/2004/nc51147892/

The Parkfield experiment

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Shaded relief map of central California showing the situation of the Carrizo Plain in the Coast Ranges. The orange line shows the surface trace of the SAF, and is thicker along the portion that is inferred to have ruptured in the 1857 earthquake [Sieh, 1978]. The blue line is adjacent to the Parkfield Segment (PS) of the SAF, while the red line is adjacent to the Cholame Segment (CS

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The Dragon's Back Pressure RidgeThis large, elongate ridge (3 km along the SAF and a maximum of 500 m wide perpendicular to the SAF) is bounded on the far side by the San Andreas fault. View direction is east-southeast. The pressure ridge is part of a complex of similar kilometer-scale ridges elongate parallel to the SAF in the southern Carrizo Plain.

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Earthquakes Earthquakes occur as sections of

the Earth’s crust slip past one another. Friction is a force that prevents these plates from sliding smoothly.

Friction – is the force that opposes motion between two surfaces that are touching.

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Origination of an Earthquake

Focus – Source of the Earthquake that originates in the interior of the Earth. Site of 1st Movement !

Epicenter – The point directly above the focus where the energy hits the surface.

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HypocenterThe hypocenter is the point within the earth where an earthquake rupture starts. The epicenter is the point directly above it at the surface of the Earth. Also commonly termed the focus.

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When an earthquakeoccurs, the elasticallystored energy iscarried outward fromthe focus to otherparts of the Earth byvibrations. Thesevibrations are calledseismic waves andspread outspherically in alldirections, just assound waves do.

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Fault

A fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture.Strike-slip

Strike-slip faults are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right lateral; if the block moves to the left, the motion is termed left lateral.Dip-slip

Dip-slip faults are inclined fractures where the blocks have mostly shifted vertically. If the rock mass above an inclined fault moves down, the fault is termed normal, whereas if the rock above the fault moves up, the fault is termed reverse. A thrust fault is a reverse fault with a dip of 45° or less. Oblique-slip faults have significant components of different slip styles.

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Fault plane The fault plane is the planar (flat) surface along which there is slip during an earthquake

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ForeshocksForeshocks are relatively smaller earthquakes that precede the largest earthquake in a series, which is termed the mainshock. Not all mainshocks have foreshocks.

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http://quake.wr.usgs.gov/recenteqs/latest.htm

Real Time Earthquakes

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Seismic WavesBody Waves: Travel outward in all directions from the focus and have the capacity to travel through the Earth's interior.

P (primary) waves – Longitudinal waves move by compression/expansion

S (secondary) waves - shearSurface Waves: Travel around but not through the Earth; they are guided by the Earth's surface.

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Body Waves

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Body Wave P Waves in Motion

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Body WaveS wave in motion

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Surface WaveL wave in motion

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TRAVELTIMEOF SEISMIC WAVES

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REFRACTIONANDREFLECTIONOF BODY WAVES

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P waves are the fastest waveS waves are slightly slowerL waves are the slowest of the

three waves

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A highly simplified simulated recording of earthquake waves (a seismogram). This seismogram is a simulation. The actual records of earthquake waves are far more complicated than what is presented here

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The magnitude is a number that characterizes the relative size of an earthquake. Magnitude is based on measurement of the maximum motion recorded by a seismograph. Several scales have been defined, but the most commonly used are (1) local magnitude (ML), commonly referred to as "Richter magnitude," (2) surface-wave magnitude (Ms), (3) body-wave magnitude (Mb), and (4) moment magnitude (Mw). Scales 1-3 have limited range and applicability and do not satisfactorily measure the size of the largest earthquakes.

Magnitude

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Richter scale

The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs.

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Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

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IntensityThe intensity is a number (written as a Roman numeral) describing the severity of an earthquake in terms of its effects on the earth's surface and on humans and their structures. Several scales exist, but the ones most commonly used in the United States are the Modified Mercalli scale and the Rossi-Forel scale. There are many intensities for an earthquake, depending on where you are, unlike the magnitude, which is one number for each earthquake.

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MohoThe Moho is the boundary between the crust and the mantle in the earth. This is a depth where seismic waves change velocity and there is also a change in chemical composition. Also termed the Mohorovicic' discontinuity after the Croatian seismologist Andrija Mohorovicic' (1857-1936) who discovered it. The boundary is between 25 and 60 km deep beneath the continents and between 5 and 8 km deep beneath the ocean floor.

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http://pasadena.wr.usgs.gov/shake/