What Are Earthquakes Science Chapter 7 Section 1 Notes Science Chapter 7 Section 1 Notes

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  • What Are EarthquakesScience Chapter 7 Section 1 Notes

  • Section VocabularyEarthquake: a movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move.Elastic Rebound: the sudden return of elastically deformed rock to its undeformed shapeSeismic Wave: a wave of energy that travels through the Earth and away from an earthquake in all directions.

  • I. Where Earthquakes HappenMost are near the boundaries of tectonic plates. Large earthquakes have occurred in the middle of the North American plate.Tectonic plates move in different directions and speeds.Can push or pull away from one another.

  • I. Where Earthquakes HappenThey can skip slowly past one another horizontally.f. Movements break crust into a series of faults.g. A fault is a break in Earths crust along which blocks of rock slide relative to one another.

  • Map of Earthquakes

  • II. Faults at Tectonic PlatesEarthquakes at Divergent Boundariesa.Two tectonic plates pull away from one another.b. Plates cause lithosphere to break into blocks and blocks drop down relative to others.c. Example: Mid-Ocean Ridge. Lithosphere is thin and weak. Because lithosphere is thin, earthquakes along the faults are shallow.

  • II. Faults at Tectonic PlatesB. Earthquakes at Convergent BoundariesTwo tectonic plates collide with one another.2 Things may happen: i.Both plates may crumple up to form mountains.ii.One plate may move underneath and sink into the mantle. This is called subduction.c. During subduction or mountain building the rocks are compressed and this breaks them into fault blocks. These create reverse faults.

  • II. Faults at Tectonic PlatesC. Earthquakes at Transform Boundariesa.Two plates move past one another horizontally (or in opposite directions).b.Rocks on both sides are sheared (broken as they grind past).c.The blocks form a series of strike-slip faults as blocks move.d.Most exist between plates made of oceanic lithosphere

  • II. Faults at Tectonic PlatesD. Fault ZonesPlaces along plate boundaries where interconnected faults are located.Have different lengths.Occur at different depths.Cut through the lithosphere in different directions.Normal, Reverse, and Strike-Slip, faults can all occur in one single fault zone.The San Andreas fault zone in California is an example.

  • III. Why Earthquakes HappenAs plates move, stress near the edges increases and rock deforms.Rock deforms mainly 2 ways:Plastic Deformation- fold and deform like clay being molded. ii. Elastic Deformation-rocks are stretched like a rubber band. This is when energy is released (earthquake).

  • III. Why Earthquakes HappenA.Elastic Rebounda. The sudden return of deformed rock to original shape.b.Happens when stress on rock becomes so great the rock breaks or fails.c.During sudden motion, energy is released and travels through rock in form of seismic waves.

  • IV. Earthquake WavesP Wavesa. P waves are Pressure or Primary WavesThe fastest seismic waves.They are the first ones detected.Can travel through solids, liquids and gases.

  • IV. Earthquake WavesS Wavesa. S waves are shear waves.b. Second- fastest seismic waves.c. Shear rock side to side.Cannot travel through parts that are completely liquid.Another name is secondary waves.

  • IV. Earthquake WavesSurface Wavesa.Move only along Earths surface.b. Produce motion only near the top of the Earths crust.c. Tend to cause most damage.d. 2 types:i.a rolling up-and-down motion.ii.Back-and-forth motion.