Chapter 32

1. Chapter 32 The Architecture of the Earth Presented by April Senger

2. Primary Waves • P waves are primary waves; the longitudinal waves generated by an earthquake • All waves carry large amounts of energy • P-waves are the fastest & travel well through solids and liquids such as in our lithosphere • P-waves are the first to arrive at the shock-wave stations so we call them the primary waves • Also called body waves Presented by April Senger

3. Secondary Waves • The S waves are secondary waves; the transverse waves generated by an earthquake • The second waves to arrive are the transverse ones so they are called secondary waves • P and S waves can cause the surface to move back/forth or up/down resulting in little damage • Also called body waves Presented by April Senger

4. Surface Waves • Surface waves are a seismic wave that travels along the Earth’s surface • Surface waves are a combination or both up/down and back/forth like a bell that has been rung and do much damage to buildings etc • Rayleigh waves move up and down and Love waves are the ship-like side to side motion Presented by April Senger

5. Seismic Stations • At least three stations are required to make measurements on each earthquake and by using the speed each wave travels at, seismologists can locate the epicenter • P waves can travel through solid and liquid where S waves can only travel through solids. We can use this data to study the layers of the Earth • We measure earthquakes with the Richter Scale Presented by April Senger

6. Concept Check • What evidence supports the theory that the Earth’s inner core is solid and the outer core is liquid? • The differences between how the P and S waves move through the Earth’s interior • At 2900 km a wave shadow develops and only S-waves are reflected indicating a liquid outer core • The P-waves hit a sudden increase in speed which tells us the center is solid (primary travel faster in solids) Presented by April Senger

7. Three Layers of the Earth • The Earth appears solid from the surface but is composed of many layers that have properties of solids and liquids. • There are three layers called the crust, mantle and core. Presented by April Senger

8. Layer Facts • The crust is the outermost and thinnest layer of the Earth • The mantle is the layer of rock between the Earth’s crust and core • The core is the center of a planetary body such as the Earth • We live on the crust and is the coolest layer made of hard solid rock Presented by April Senger

9. More Facts • The oceanic crust is only 4-7 miles thick and the continental crust is 12-25 miles thick and is less dense then oceanic crust • The thickest part of our crust is 70 km thick • The mantle is more dense and is 1800 mi (2900 km) thick • The mantle is 80% of the Earth’s volume Presented by April Senger

10. Facts Again… • We use geologic events such as volcanoes etc to study the mantle since we have never been there • The upper part of the mantle is cooler and stiff as it approaches the crust • The lower part of the mantle is hot and plastic (like gum) • The core consists of an outer core that is liquid metal and an inner core that is solid. Both are thought to be mainly iron and nickel Presented by April Senger

11. Asthenosphere and Lithosphere • Lithosphere is the thin outer shell of the Earth, consisting of the crust and the rigid upper mantle • Asthenosphere is the zone of the mantle beneath the lithosphere that consists of slowly flowing solid rock Presented by April Senger

12. The lithosphere is 60 miles thick The lithosphere is made of 7 large pieces and several smaller ones called tectonic plates Plates can move away from each other, together, or even along each other Plates can move between 1 to 16 cm per year Convection currents or the flow of hot less dense material with dense cooler material is thought to be responsible for the plate movement More Astheno and Litho Info Presented by April Senger

13. Concept Check • If you wished to drill the shortest hole to the mantle, would you drill into western Colorado or in Florida? • You should drill in Florida because it is thinner crust • Project MoHole in the East Pacific Ocean is doing just this Presented by April Senger

14. Folds • If you have a rug on the floor and push it together you might notice folds • The Earth’s crust does the same thing under compressive stress • Syncline is when the fold is in the shape of a “U” • Anticlines are folds that are an upside down “U” Presented by April Senger

15. Fault • When compressional stress is stronger than rock, the rock fractures into two parts • Footwalls are where you can stand and Hanging Walls are where you could potentially hang a lantern as named by miners • Faults can slide up , down or horizonally Presented by April Senger

16. Reverse & Normal Faults • The Rocky Mountain, Canadian Rockies, and Appalachians are Reverse Faults where the Hanging Wall creates a ledge over the Footwall • Normal Faults are caused by compression and tension • Nevada, Eastern California, Southern Oregon, Southern Idaho and Western Utah have a fault where the fault plane slides down with no ledge Presented by April Senger

17. Strike Slip Faults • California’s San Andreas fault has mostly horizontal motion instead of vertical motion • The Great San Francisco Earthquake and Fire of 1906 registered a 8.3 on the Richter scale • It caused 700 deaths and extensive fire damage • Note the picture on page 579 of the moving orchard Presented by April Senger