Geology Homework 1

When a fault is expressed at the surface, it is called a __________. - fault scarp The name of the site where slippage begins and earthquake waves radiate outward is called the __________. - hypocenter If the stress applied to the rock is greater than rock strength, what happens? - Blocks of rock will slide relative to one another along a fault, causing an earthquake. The hanging wall moves __________ relative to the footwall in a __________ fault. down; normal Which of the following might be seen where strike-slip movement has occurred? - offset fences Which of the following responses best describes the epicenter of an earthquake? - The point on Earth's surface directly above the focus of an earthquake. In calculating the location of the epicenter of an earthquake, which of the following factors is most useful? - the difference in arrival time of P and S waves In addition to a travel-time graph, at least how many seismograph stations are needed to determine the location of the epicenter of an earthquake? - three As the distance between the epicenter of an earthquake and a seismograph station increases, so does the difference in the arrival times of the P and S waves. What causes this? - P waves are faster than S waves. Which statement provides the best explanation of why most earthquakes occur at plate boundaries? - Plate boundaries are locations on Earth where portions of the lithosphere interact as they move past each other. What do we call seismic waves that are transmitted along the outside of Earth? surface waves Which of the following motions best describes the movement of S waves as they travel through rocks following the release of energy during an earthquake? - shaking particles at right angles to the direction of travel Which of the three types of seismic waves travels through rock with the greatest velocity? - P waves Which of the following types of seismic body waves travels only through solids? - S waves Early in the study of earthquakes, seismologists learned that P waves arrive at seismograph stations all over Earth, but a shadow zone exists for S waves. Which of the following responses best explains this phenomenon? - The outer core of Earth is liquid. Which type of seismic waves generally cause the most structural damage as they travel through Earth? - surface waves Define earthquake intensity. - A qualitative measure of the amount of ground shaking at a certain location. A smaller earthquake in Virginia was felt over a larger distance, as compared to a larger earthquake in California. What is a reason this occurred? - colder crust Richter magnitude (ML) is derived from measuring __________ and __________, and then plotting them on a Richter diagram. - S minus P wave time; maximum S wave height Why is moment magnitude (MW) preferred over Richter magnitude (ML)? - Moment magnitude measures the total energy released during an earthquake and can adequately measure the energy of large earthquakes. How are tsunamis generated? - Through displacement of the seafloor under water What is a tsunami? - a series of water waves that travel away from a fault in all directions at high speed Why do ships at sea tend not to notice tsunamis? - Tsunamis in deep water have small wave height and long wavelength. Why does the wave height of a tsunami increase as the tsunami enters shallow water? In shallow water, the energy of the tsunami must be contained within a smaller water column. What type of plate boundary are most tsunamis associated with? - convergent plate boundaries Which ocean is associated with most tsunamis? - Pacific Ocean Will Sumatra experience another tsunami like the destructive one of December 2004? This is likely, because Sumatra is near many ocean trenches. Which of the following best describes liquefaction? - the transformation of stable soil into loose, liquefied material that is able to rise toward Earth's surface Describe how sand volcanoes form - An earthquake causes loose, saturated sandy material to liquefy, shoot upward through fractures of a confining unit, and eventually erupt at the surface. __________ in the sandy layer causes the ground to subside after sand volcanoes form. - Tighter packing Structures built on __________ will become unstable during an earthquake. - loose, saturated sediments