GS 106 - Introduction to Physical Geology

16-1 through 20-1

16) Name and describe the 3 types faults. Tell me which type defines a subduction zone.

Answer: The first fault is a normal fault, which is caused by tension and the hanging wall moves down relative to the footwall. The second type of fault is a reverse fault, which are created by tension and the hanging wall moves up relative to the footwall. The last type of fault is a transform fault, where the fault blocks move horizontally side by side. A subduction zone would be considered a thrust fault, which is a low angle reverse fault.

17) What is the definition of plate tectonics and what are 3 different lines of evidence used to prove the theory?

Answer: The theory of plate tectonics says that the lithosphere (crust) is broken up into plates that move relative to each other due to heat flow in the athenosphere (mantle). Three lines of evidence for plate tectonics would be volcanoes (volcanic arcs), mountain chains, and most earthquakes (also shapes of the continents that fit together like a puzzle, similar fossils on different continents, trenches, mid-ocean ridges, paleocliamte indicators, the age of the ocean floor, and similar rocks on different continents).

18) Name and describe the two scales used to measure earthquake magnitude?

Answer: The two scales are the Richter scale and the Mercalli Intensity scale. The Richter scale is a logarithmic scale used to express the total amount of energy released by an earthquake. The Mercalli Intensity scale measures the effects of an earthquake after the earthquake has occurred and measures things like mortality, damage, and things of that nature.

19) Name and describe the 4 general layers of the Earth including their composition, relative temperature, and phase.

Answer: The outer most layer is the crust, which is solid and brittle and broken into plates. The crust is quart-rich and is the coolest layer. The mantle is warmer than the crust, is composed of iron and magnesium (ferromagnesian rocks) and is solid. The Outer core is liquid, is composed of iron and nickel, and is hotter than the mantle. Lastly, the inner core is solid, also composed of iron and nickel, and is the hottest layer of all.

20) Name and describe the 3 types of convergent plate boundaries and how the plates react when they converge. What type of convergent plate boundary can be found on Oregon’s coast?

Answer: The first type of convergent plate boundary is an oceanic-oceanic plate boundary, and as they collide the older, denser plate is subducted. The second type of convergent plate boundary is a continental-oceanic plate boundary where the denser oceanic plate is subducted underneath the continental plate. The last type of convergent boundary is a continental-continental boundary where there is no subduction because the plates are the same density. Instead large mountain change form as the plates collide and the crust buckles and thickens. On our coast we have a continental-oceanic plate boundary.

16-2 through 20-2

16) Name and describe the 3 types of plate boundaries. Tell me which type can be found off the coast of Oregon State?

Answer: The first type of plate boundary is a divergent boundary where the plates pull apart from each other. The second type of plate boundary is a convergent boundary where the plates push together. The last type of plate boundary is a transform boundary where the plates move horizontally side by side. The type of plate boundary found off the Oregon coast is a convergent plate boundary.

17) Describe the 3 ways magma is created and tell me which is the cause for the formation of the Cascade Volcanic Arc.

Answer: Magma is formed through the addition of heat at hotspots. Magma can also be formed by the release of pressure at a divergent plate boundary, and lastly magma can form through the addition of water, which lowers the melting point of minerals and occurs in subduction zones. The Cascades are formed by addition of water to the mantle by the subduction of the Juan de Fuca plate under the North American plate.

18) Name and describe the 2 types of crust including their specific density and thickness as well as their composition.

Answer: Continental crust is between 35-40 km thick, has a density of 2.7 g/cm3, and is composed of granite. Oceanic crust is 7-10 km thick, has a density of 3.0 g/cm3, and is composed of basalt.

19) Name and describe the four types of seismic waves.

Answer: The first type of seismic wave is a P-wave (primary wave). It is the first wave to show up on a seismometer during an earthquake and is a compressional wave. The second type of wave is the s-wave (secondary wave) and is the second to show up on a seismometer. It is perpendicular to the p-wave and creates the shaking. The third wave is a Rayleigh wave, which is associated with ground roll. The fourth wave is a Love wave, which is associated with horizontal shifting of Earth’s surface.

20) Describe the formation of a tsunami, how fast they wave can move in the open ocean, and how is reacts as it approaches land. Which coast of the United States is most vulnerable to the possibility of tsunamis?

Answer: A tsunami forms due to the down drop or upthurst of the Earth’s crust that is a result of an earthquake and that movement displaces water above the plate movement. Tsunamis can move up to 500 miles per hour in the open ocean. As the wave approaches land it slows down and increases in height. The Pacific coast or the west coast of the United States is the most likely to be hit by a tsunami.