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