chapter 3

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Austin Community College District *

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1309

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Geology

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Apr 3, 2024

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docx

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Chapter 3 review • Compare and contrast the different types of faulting Faults are fractures in the Earth's crust where movement has occurred. There are three main types: normal faults (caused by tensional forces, with the hanging wall moving downward relative to the footwall), reverse faults (caused by compressional forces, with the hanging wall moving upward relative to the footwall), and strike-slip faults (caused by horizontal shear forces, with lateral displacement along the fault). o How do we define an active fault versus an inactive fault? An active fault is one that has experienced movement in the recent geological past and is likely to move again in the future. Inactive faults, on the other hand, have not experienced movement for a significant period and are not expected to move in the near future. • Explain the formation of seismic waves o Know the different types of seismic waves generated during an earthquake (P, S, and surface) and how they move through the earth. Seismic waves are produced by the sudden release of energy during an earthquake. There are three main types of seismic waves: Primary (P) waves, Secondary (S) waves, and Surface waves. P waves are compressional waves that travel fastest and can move through solids, liquids, and gases. S waves are shear waves that follow P waves and can only move through solids. Surface waves are slower waves that travel along the Earth's surface and cause most of the damage during earthquakes. o Which seismic wave is most destructive, and why? Surface waves are the most destructive because they cause the most intense ground shaking and have the longest durations • Summarize the processes that lead to an earthquake and the release of seismic waves o Summarize the elastic rebound model Elastic Rebound Model: This model explains how stress builds up along a fault until it exceeds the strength of the rocks, causing them to rupture and release stored energy as an earthquake. o Know the typical relationship between depth of focus of an earthquake and the amount of damage it is likely to cause. Depth of Focus vs. Damage: Generally, deeper earthquakes cause less damage than shallow ones because the energy is dissipated over a larger area. o What is the relationship between focus and epicenter? The focus is the point within the Earth where an earthquake originates, while the epicenter is the point on the Earth's surface directly above the focus.
o How do lag times change as you move further from the epicenter of an earthquake? Lag times increase as distance from the epicenter increases because seismic waves travel at finite speeds. o How does ground shaking change depending on different kinds of earth materials? Ground Shaking: Ground shaking varies depending on the type of Earth materials present. Soft, loose materials tend to amplify ground shaking, while hard, dense materials dampen it. (Understand material amplification.) o What is unusual about the New Madrid, Missouri earthquakes? The New Madrid earthquakes were unusual because they occurred in the central United States, far from tectonic plate boundaries. o In what ways do we try to predict earthquakes? Scientists use various methods such as seismic monitoring, historical data analysis, and geodetic measurements to try to predict earthquakes. o How does the inverse magnitude/frequency relationship apply to earthquakes? This relationship states that small earthquakes occur much more frequently than large ones. • Differentiate between the magnitude scales used to measure earthquakes o Know how the Richter scale and the moment magnitude scale measure earthquake magnitude, and what the differences are between the two scales. Richter Scale vs. Moment Magnitude Scale: The Richter scale measures the amplitude of seismic waves, while the moment magnitude scale measures the total energy released by an earthquake, the amount of slip the rigidity of the rocks. It is much way better to estimate how much energy was released. From 5 to 6 magnitude EQ is 32 times than. o Why do scientists prefer the moment magnitude scale? Scientists prefer the moment magnitude scale because it provides a more accurate representation of an earthquake's size. o What is the difference between magnitude and intensity? Magnitude refers to the size of an earthquake, while intensity refers to the effects of an earthquake at a particular location. o Know how the Mercalli intensity scale is assigned to a location The Mercalli scale assigns intensity values based on observed effects at specific locations. This is subjective and descriptive but not reliable.
• Identify global regions at most risk for earthquakes, and describe the effects of earthquakes o Determine where most earthquakes occur, with respect to plate tectonics. Why do they occur there? Most earthquakes occur along plate boundaries, especially convergent boundaries where subduction zones are present. o List the factors that determine whether a building with withstand ground shaking Building design, construction materials, and local geology all influence whether a building will withstand ground shaking. • Describe how earthquakes are linked to other natural hazards o List the primary and secondary hazards Primary hazards of earthquakes include ground shaking, surface rupture, and tsunamis. Secondary hazards include landslides, liquefaction, and fires. o What is liquefaction? In what kind of earth material does it occur? Liquefaction occurs when saturated soil loses its strength and behaves like a liquid during shaking, often leading to ground failure and structural damage. It typically occurs in loose, sandy soils. Key terms: o strike-slip fault: Horizontal motion only-left lateral and right lateral o normal fault: normal tensión where blocks are falling apart o reverse fault: blocks are being shoved together o epicenter: is above where that focus occurred. o focus: point in the ground where the fault first ruptures during and earthquake o material amplification: Which of the following are ways for communities to deal with the earthquake hazard? retrofit old buildings enact building codes for new construction provide insurance for potential victims educate people on what to do during an earthquake All of the above are ways for communities to deal with the earthquake hazard
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