2 An Earthquake is…the shaking and trembling that results from the movement of rock beneath Earth's surfaceThe movement of Earth's plates produce strong forces that squeeze or pull the rock in the crustThis is an example of stress, a force that acts on rock to change its volume or shape
3 StressThere are three different types of stress that occur on the crust, shearing, tension, and compressionThese forces cause some rocks to become fragile and they snapSome other rocks tend to bend slowly like road tar softened by the suns heat
4 - Forces in Earth’s Crust Types of StressStress that pushes a mass of rock in two opposite directions is called shearing.
5 - Forces in Earth’s Crust Types of StressThe stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.
6 - Forces in Earth’s Crust Types of StressThe stress force called compression squeezes rock until it folds or breaks.
7 FaultsA fault is a break in the crust where slabs of crust slip past each other. The rocks on both sides of a fault can move up or down or sidewaysWhen enough stress builds on a rock, the rock shatters, creating faultsFaults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust too much so the crust smashes
8 Kinds of Faults- Forces in Earth’s CrustTension in Earth’s crust pulls rock apart, causing normal faults.
9 Kinds of Faults- Forces in Earth’s CrustA reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.
10 Kinds of Faults- Forces in Earth’s CrustIn a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up and down motion.
11 Strike-Slip Faults Shearing creates this fault In this fault, rocks on both sides of the fault slide past each other with a little up and down motionWhen a strike-slip fault forms the boundary between two plates, it becomes a transform boundary
12 Mountains Formed by Folding Folds are bends in rock that form when compression shortens and thickens part of Earth's crustMOUNTAINS FORMThe crashing of two plates can cause folding and compression of crustThese plate collisions can produce earthquakes because rock folding can fracture and lead to faults
13 Anticlines and Synclines Geologists use the terms syncline and anticline to describe downward and upward folds in rockAn anticline is a fold in a rock that arcs upwardA syncline is a fold in a rock that arcs downwardThese folds in rocks are found on many parts of the earths surface where compression forces have folded the crust
14 How Earthquakes FormEarthquakes will always begin in a rock beneath the surfaceA lot of earthquakes begin in the lithosphere within 100 km of Earth's surfaceThe focus triggers an earthquakeFocus: the point beneath Earth's surface where rock that is under stress breaks
15 Seismic WavesSeismic Waves: vibrations that travel through Earth carrying the energy released during an earthquakean earthquake produces vibrations called waves that carry energy while they travel out through solid materialDuring an earthquake, seismic waves go out in all directions to the focusThey ripple like when you through a stone into a lake or pond
16 Seismic Waves There are three different types of seismic waves: P waves,Secondary or S waves, and surface wavesAn earthquake sends out two of those waves, P and S wavesWhen they reach the top of the epicenter, surface waves form
17 Primary Waves Also known as P Waves The first waves to come are these wavesP waves are earthquake waves that compress and expand the ground like an accordionP waves cause buildings to expand and contractTravel through BOTH liquids and solids
18 Secondary Waves Also known as S Waves After P waves, come S waves S waves are earthquake waves that vibrate from one side to the other as well as down and upThey shake the ground back and forthWhen S waves reach the surface, they shake buildings violentlyUnlike P waves, which travel through both liquids and solids, S waves cannot move through any liquids
19 Surface WavesWhen S waves and P waves reach the top, some of them are turned into surface wavesSurface waves move slower than P waves and S waves, but they can produce violent ground movementsSome of them make the ground roll like ocean wavesOther surface waves move buildings from side to side
20 Detecting Seismic Waves Geologists use instruments called seismographs to measure the vibrations of seismic wavesSeismographs records the ground movements caused by seismic waves as they move through the Earth
21 Mechanical Seismographs Until just recently, scientists have used a mechanical seismographa mechanical seismograph consists of a heavy weight connected to a frame by a wire or springWhen the drum is not moving, the pen draws a straight line on paper wrapped around the drumSeismic waves cause the drum to vibrate during an earthquakethe pen stays in place and records the drum's vibrationsThe higher the jagged lines, the more severe earthquake
22 Instruments used to detect movement In trying to predict earthquakes, geologists have developed instruments to measure changes in elevation, tilting of the land surface, and ground movements along faults.
23 Measuring Earthquakes There are at least 20 different types of measuresMain 3: the Mercalli scale,Richter scale,and the Moment Magnitude scaleMagnitude is a measurement of earthquake strength based on seismic waves and movement along faultsMercalli – INTENSITY, based on effects
24 The Richter ScaleThe Richter scale is a rating of the size of seismic waves as measured by a particular type of mechanical seismographDeveloped in the 1930’sAll over the world, geologists used this for about 50 yearsElectric seismographs eventually replaced the mechanical ones used in this scaleProvides accurate measurements for small, nearby earthquakesDoes not work for big, far ones
25 The Moment Magnitude Scale Geologists use this scale todayIt’s a rating system that estimates the total energy released by an earthquakeCan be used for any kind of earthquakes, near or farSome news reports may mention the Richter scale, but the magnitude number they quote is almost always the moment magnitude for that earthquake
26 Locating the Epicenter Since the P waves travel faster than the S waves, scientists can use the difference in arrival times to see how far away the earthquake occurred.It does not tell the direction however.
27 Determining Direction One station can only learn how far away the quake occurred.They would draw a circle at that radius.If three stations combine their data, the quake occurred where the three circles overlap.
28 Locating the Epicenter - Earthquakes and Seismic WavesTRIANGULATION is used to detect the location of the epicenter
29 How Earthquakes Cause Damage The severe shaking provided by seismic waves can damage or destroy buildings and bridges, topple utility poles, and damage gas and water mains.With their side to side, up and down movement, S waves can damage or destroy buildings, bridges, and fracture gas mains.
30 Earthquake Risk- Earthquake SafetyGeologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred.
31 How Earthquakes Cause Damage - Earthquake SafetyHow Earthquakes Cause DamageIn addition to the DANGERS of ground shaking, earthquakes can cause tsunamisA tsunami spreads out from an earthquake's epicenter and speeds across the ocean.
32 Designing Safer Buildings - Earthquake SafetyTo reduce earthquake damage, new buildings must be made stronger and more flexible.