2 Earthquakes General features Vibration of Earth produced by the rapid release of energy.Focus – the place within Earth where earthquake starts.Epicenter - Point on the surface, directly above the focusCaused by slippage along a break in the lithosphere, called a fault.Fault: Fracture in earth where movement has occurred.
4 Earthquakes Types of Faults (draw and label each fault type on right) Normal Fault: Fault in which the rock above the fault plane has moved down relative to the rock below.Reverse Fault: Fault in which the material above the fault plane moves up relative to the material below.
5 Earthquakes Types of Faults (draw faults on right) 3. Thrust Fault: Reverse fault with a dip less than 45 degrees.4. Strike-slip fault: A fault along which the movement is horizontal and parallel to the trend of the fault.
6 The Cause of Earthquakes Deformation of RocksForces within Earth slowly deform the rock that makes up Earth’s crust causing the rock to change shape, or bend on both sides of a fault.When the rocks bend they store energy, much like a rubber band when stretched.
7 The Cause of Earthquakes Elastic Rebound sequence of events…Stored energy builds as the rock is deformed.Suddenly the rocks slip, or break at their weakest point (the focus) and the stored energy is released all at once.The deformed rock ‘springs back’ to its original shape. This is called elastic rebound.
16 Earthquakes Earthquake waves Types of earthquake waves Surface waves (occurs when an S-wave reaches the surface)Travel slower than P-waves and S-wavesMove up and down as well as side to side (similar to an ocean wave)Most destructive seismic wave
18 Earthquakes Earthquake intensity and magnitude Intensity Magnitude A measure of the degree of earthquake shaking at a given locale based on the amount of damageMost often measured by the Modified Mercalli Intensity ScaleMagnitudeConcept introduced by Charles Richter in 1935
19 Earthquakes Earthquake intensity and magnitude Magnitude (M) Often measured using the Richter ScaleBased on the amplitude of the largest seismic waveA tenfold increase in wave height equals an increase of 1 on the Richter scale.Does not estimate adequately the size of very large earthquakes.Scientists no longer use it routinely.
20 Earthquakes Earthquake intensity and magnitude Magnitude Moment magnitude scaleMeasures very large earthquakesDerived from the amount of displacement that occurs along a fault zoneMore precise than the Richter Scale
21 Magnitude 5 or greater earthquakes over 10 years
22 Earthquakes Locating an earthquake Located using the difference in the arrival times between P and S wave recordings, which are related to distance (Travel-time graph)
23 Travel-time graphHow long does it take a P wave and and S wave to travel 1000 km?P-wave =S-wave =Which seismic wave is faster?
24 Earthquakes Locating an earthquake Epicenter At least three station recordings are needed to locate an epicenterCircle equal to the epicenter distance is drawn around each stationPoint where three circles intersect is the epicenter
25 The epicenter is located using three or more seismic stations
26 Earthquakes Causes of Earthquake Damage Earthquake-related hazards Seismic shakingLiquefactionLandslidesMudflowsTsunamis
27 Earthquakes Earthquake destruction Destruction results from … Seismic shaking (the ground vibrating)May jolt and twist structuresUnreinforced brick or concrete structures may collapseLiquefaction of the groundSaturated soil material turns fluidUnderground objects may float to surface
29 Damage from the 1964 Anchorage, Alaska, earthquake
30 Earthquakes Earthquake destruction Destruction resulting from… Landslides and MudflowsMovement of loose rock and soil down slopeIf the water content of the soil is high an earthquake can start a mudflow
33 Earthquakes Earthquake destruction Destruction resulting from… TsunamisOcean wave formed when the ocean floor suddenly shifts.Move fast (100+ km/hr) across the open oceanA Tsunami slows down and increases in size as it approaches shore