Earthquakes!

The magnitude of an earthquake is a number that represents the

• arrival time of the first P-wave

• difference in arrival times between P- and S-waves

• distance to the epicenter

• energy released by an earthquake

A seismic station recorded the P-waves, but no S-waves, from an earthquake because S-waves were

• absorbed by Earth's outer core

• transmitted only through liquids

• weak and detected only at nearby locations

• not produced by this earthquake

Base your answer on the cross section of Earth and on your knowledge of Earth science. The cross section represents the pattern of seismic wave movement away from an earthquake. Point W represents a location at the boundary between two layers of Earth's interior. Points X, Y, and Z represent seismic stations on Earth's surface. Which statement best explains why no S-waves were received directly from this earthquake at some seismic stations?

• An interior Earth layer absorbs S-waves.

• Earth's mantle reflects S-waves.

• S-waves travel slower than P-waves

• S-waves travel only on Earth's surface.

Base your answer on the diagram, which shows models of two types of earthquake waves. Model A best represents the motion of earthquake waves called

• P-waves (compressional waves) that travel faster than S-waves (shear waves) shown in model B

• P-waves (compressional waves) that travel slower than S-waves (shear waves) shown in model B

• S-waves (shear waves) that travel faster than P-waves (compressional waves) shown in model B

• S-waves (shear waves) that travel slower than P-waves (compressional waves) shown in model B

The diagrams show demonstrations that represent the behavior of two seismic waves, A and B. Which statement concerning the demonstrated waves is correct?

• Wave A represents a compressional wave, and wave B represents a shear wave.

• Wave A represents a shear wave, and wave B represents a compressional wave.

• Wave A represents compressional waves in the crust, and wave B represents compressional waves in the mantle.

• Wave A represents shear waves in the crust, and wave B represents shear waves in the mantle.

A strong earthquake that occurs on the ocean floor could result in the formation of

• a tsunami

• a delta

• an El Niño event

• an ocean current

Base your answer on the map and the modified Mercalli scale shown. The map shows the intensities of the earthquake that occurred slightly southwest of New Madrid, Missouri, on December 16, 1811. The epicenter of this earthquake is represented by *. The Roman numerals on the map show zones of earthquake intensities determined by using the modified Mercalli scale. The intensity numbers shown on the map were determined by

• the arrival time of the first P-wave recorded at each city

• the recorded time difference in the arrival of the first P-wave and S-wave at each city

• observations made at different locations during and after the earthquake

• observations made only at the earthquake epicenter

The cross section of Earth shows a P-wave moving away from an earthquake epicenter to seismic station A. No S-waves arrive directly at seismic station A because

• some parts of the core are liquid

• S-waves travel too slowly

• the distance to seismic station A is too great

• seismic station A is located on glacial ice

What usually causes tsunamis?

• hurricanes

• high-pressure weather systems

• undersea earthquakes

• the collision of ocean currents

A seismic station received the P-waves generated by an earthquake but did not receive the S-waves. Which statement best explains the absence of the S-waves?

• The earthquake was too weak to produce S-waves.

• The earthquake's epicenter and focus were at the same location.

• The S-waves were absorbed by a fluid layer as they traveled toward the seismic station.

• The S-waves were reflected away from the seismic station when they reached the Moho interface.