Earth’s Dynamic Crust

I. Evidence of Crustal Movement: A. Original Horizontality: assumes that sedimentary rock is deposited in flat layers.

B. Types of Crustal Activity: 1. Faulting: cracks within Earth’s crust. 2. Folding: bending of rock layers 3. Tilting: rock layers pushed on an angle.

Types of Folds Monocline Overturned Recumbent

II. Earthquake: the vibration or shaking of earth’s crust caused by seismic waves. A. Types of Seismic Waves: 1. Primary Waves: “P” waves are compressional waves that travel fast through both liquids and solid rock.

2. Secondary Waves: “S” waves are shear waves that travel slowly through solid rock only.

Surface Waves

III. Earthquake Location: A. Focus: the point below earth’s surface where the earthquake originates. B. Epicenter: the point on Earth’s surface straight above the focus. Earthquake Video – 2:55

Types of faults Normal fault Reverse fault Strike-slip fault

C. Calculating Epicenter Distance: requires the difference in arrival times of “P” and “S” waves to a seismic station. * The further the seismic station is from the epicenter the greater the difference in arrival time between the two waves.

Difference in arrival time between P and S waves = 3 minutes, 20 seconds

P and S wave arrival time difference of 3 min. 20 sec. Make marks on travel time axis. Drag that distance, keeping parallel to the time axis, to find the matching distance between the P line and S line. Follow line down to determine the distance from the epicenter.

Difference in arrival time between P and S waves = 3 minutes, 20 seconds 2000 Km from epicenter. Time traveled for P-wave was 4 minutes Time traveled for S-wave was 7 min., 30 sec. Time of origin for EQ = P-wave arrival time minus P-wave travel time. 8:08 a.m. – 0:04 = 8:04 a.m.

D. Epicenter Location: requires 3 seismic station readings D. Epicenter Location: requires 3 seismic station readings. Where all 3 intersect is the epicenter. Called triangulation.

E. Measuring Earthquake Strength: 1. Mercalli Scale: measures the earthquake’s intensity based on the description of the damaged caused. *larger number indicates greater damage.

2. Richter Scale: a magnitude scale used to describe the amount of energy released by an earthquake. Each step increase represents an increase of 10 times the next lower number. Ex. A magnitude 7 is 10 times greater than a 6, but 100 times greater than a mag. 5.

IV. Earth’s Layers: Earth is divided into four major zones: crust, mantle, outer core and inner core. A. Crust: “lithosphere” outer most layer and relatively thin (10-65 kilometers). 1. Continental Crust: *thicker *mostly granite *low density 2.7 g/cm3 2. Oceanic Crust: *thin *mostly basalt *more dense 3.0 g/cm3

B. Mantle: located below the crust B. Mantle: located below the crust. Separated from the crust by the Moho interface. 1. Asthenosphere: “upper mantle” flows like a thick plastic fluid – highly viscose 2. Stiffer Mantle: thicker and more solid.

C. Outer Core: made up of liquid iron. D. Inner Core: made up of solid iron and nickel. 1. Meteorites: are composed of similar material (Fe and Ni) as Earth’s inner core.

2. Shadow Zone: a dynamic band around Earth that receives no “P” or “S” from an earthquake epicenter. a. “S” waves are absorbed by the liquid outer core. b. “P” waves are refracted (bent) due to the different densities of Earth’s layers.

1. Continental coastlines fit like a jigsaw puzzle. V. Continental Drift: theory proposed by Alfred Wegener stating that Earth’s crust is shifting. A. Wegener’s Evidence: 1. Continental coastlines fit like a jigsaw puzzle. 2. Similar rocks, minerals and fossils found on separate continents. 3. Tropical plant fossils found in Antarctica. Video – 2:23

Arrows indicate direction of movement. VI. Plate Tectonics Theory: states that Earth’s crust is divided into large plates riding on the asthenosphere. *plates can consist of continental crust, oceanic crust or both. Ref. Table pg. 5 Arrows indicate direction of movement. Video – 4:15 Mt. formation from plate collision Video – 5:45 Shifting plates

A. Mantle Convection Currents: are believed to be the driving force behind plate movement. Hot, less dense magma rises at mid ocean ridges and pushes plates apart. Video – Inner structure 5:43

B. Evidence of Plate Tectonics: 1. Seafloor Spreading: new ocean crust is formed by rising magma at mid-ocean ridges. *the further from the ridge the older the rock! Video – What causes tectonic activity – 6:04 Video - Ocean Floor clues to continental drift – 5:43

2. Magnetic Reversals: Earth’s magnetic poles reverse over time creating a pattern in newly formed ocean crust. *magnetic minerals in the new rock align themselves with Earth’s magnetic field. *identical magnetic patterns are found on both sides of the ocean ridge.

1. Convergent Boundary: two plates collide with each other. C. Plate Boundaries: the interface between plates where earthquakes and volcanoes occur. 1. Convergent Boundary: two plates collide with each other. *subduction: occurs if dense ocean crust collides with continental crust, creating deep ocean trenches. http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_subduction.html

2. Divergent Boundary: where two plates are moving apart 2. Divergent Boundary: where two plates are moving apart. Occurs at mid-ocean ridges.

3. Transform Boundary: two plates slide past each other. Ex 3. Transform Boundary: two plates slide past each other. Ex. San Andreas fault Video – Plate boundaries - 6:08 Video – San Andreas - 6:40

Volcano An opening in Earth’s crust (vent) through which magma erupts and the mountain built by the erupted material

Ring of Fire, Mediterranean Belt & Mid Atlantic Ridge Video – volcanoes – 4:12

4. Hot Spots: plumes of hot magma from the mantle producing volcanoes. *as a plate moves over the hot spot, chains of volcanic mountains form. Ex. The Hawaiian islands. http://www.wwnorton.com/college/geo/egeo2/content/animations/2_6.htm

VII. Tsunamis: large ocean waves generated by seismic activity on the ocean floor. Animation by Japan's National Institute of Advanced Industrial Science and Technology. Each frame is a ten-minute interval; the whole thing covers the first 180 minutes of the tsunami.

Helpful Links http://geology.com/plate-tectonics.shtml http://earthquake.usgs.gov/earthquakes/recenteqsanim/ http://www.learner.org/interactives/dynamicearth/structure.html