Earth Science Chapter 12(Earthquakes) Section 2(Studying Earthquakes) – Flashcards
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What is the study of earthquakes and seismic waves called?
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seismology
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seismograph
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an instrument that records vibrations in the ground
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Name the types of motion that a modern three-component seismograph records
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One device records the vertical motion of the ground. The other two devices record horizontal motion, one for east-west and the other for north-south motion.
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How do seismographs record motion?
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by tracing wave shaped lines on paper or by translating the motion into electronic signals
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Seismogram
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A tracing of earthquake motion that is recorded by a seismograph
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Why are P waves the first waves to be recorded by a seismograph?
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Because they are the fastest-moving seismic waves
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What is the second type of wave to be recorded by a seismograph?
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S waves
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What type of wave is the lowest, and therefore the last to be recorded by a seismograph?
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Surface waves
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Scientists determine the distance to an epicenter by analyzing
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the arrival times of the P waves and S waves
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The longer the lag time between the arrival of the P waves and the S waves
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the farther away the earthquakes occured
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Before computers were widely available, scientists consulted a lag-time graph to determine how far an earthquake occured from
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the earthquake's epicenter
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A lag-time graph translates the difference in an arrival times of the P waves and S waves into distance from the epicenter to
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each station
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What can a lag-time graph determine about an earthquake?
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its start time
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Before computers were widely available, what either, less precise technique did scientists use to locate the epicenter of an earthquake?
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maps
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On the maps, what did the radius of each circle represent?
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the distance from that station to the earthquake's epicenter
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Where would the epicenter of the earthquake be found on the map?
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the point at which all the circles interested
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Scientists who study earthquakes are interested in the amount of
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energy released by an earthquake
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Magnitude
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the measure of the strength of an earthquake
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Richter scale
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a measurement system that bases earthquake strength on ground motion
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Moment magnitude
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the measure of earthquake strength based on the size of the area of the fault that moves, the average distance that the fault block moves, and the rigidity of the rocks in the fault zone
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intensity
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the amount of damage caused by an earthquake
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modified Mercalli scale
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a measurement system that expresses earthquake intensity in Roman numerals and describes the effects of each intensity
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Which magnitude scale was widely used for most of the 20th century?
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the Richter scale
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Which magnitude scale do scientists generally prefer now?
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the moment magnitude scale
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For what do the Richter scale and the moment magnitude scale provide similar values?
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for small earthquakes
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What is the moment magnitude scale more accurate for measuring?
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large earthquakes
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What is the highest moment magnitude recorded for an earthquake so far?
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a moment magnitude of 9.5 in Chile
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What was the moment magnitude of the earthquake in China in 2008 that devastated the country just before it hosted the Olympic Games?
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7.9
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What is the moment magnitude of the earthquakes that are generally not felt by people?
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less than 2.5
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How is Intensity I described on the modified Mercalli intensity scale?
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Intensity I is not felt except by very under specially favorable conditions
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How is Intensity XII described on the modified Mercalli intensity scale?
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Causes total destruction, distorts lines of sight, objects are thrown into the air
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Upon what does the intensity of an earthquake depend?
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on the earthquake's magnitude, the distance between the epicenter and affected area, the local geology the earthquake's duration, and human infrastructure
