Measuring the Force of Earthquakes

seismology

scientific study of earthquakes

A seismograph records an earthquake, but scientists do not feel it. The earthquake has a magnitude _____.

<2.0

The farther apart the P and S waves are on a seismogram, the farther away is the epicenter of an earthquake. True or False?

The farther away the source or epicenter of the earthquake, the farther apart the P waves and the S waves will arrive.

The focus is the point underground where rock layers first move during an earthquake. True or False?

True, the epicenter is the point on the surface directly over the focus of the earthquake. The focus is the point underground where the rock layers first move, and from where seismic waves travel in all directions.

Select all of the answers that apply. Triangulation is a process to locate an earthquake. Which statements are true regarding this process?

You must know the difference in the times that S waves and P waves arrive at a seismograph station to determine the distance to the epicenter. You should draw a line from the center of the seismograph station to the epicenter to show its location. Three seismograph distances must be mapped with circles and the point where they intersect is the epicenter.

seismogram

a record of the time and intensity of the energy waves produced by an earthquake

seismic gaps

areas on active faults where a major earthquake hasn't occurred in a long time

Which of the following are signs that an earthquake may occur?

changes in air temperature changes in water levels in wells foreshocks aftershocks changes in the magnetic properties of rocks

The area where rock layers first move along a fault is the _____ of an earthquake.

epicenter

seismograph

instrument used to record and measure vibrations from earthquakes or earth tremors

magnitude

measure of the total amount of energy released during an earthquake

foreshocks

mini-quakes that usually occur before a major earthquake

moment magnitude scale

newer magnitude scale that measures the amount of moved (displaced) rock along a fault to determine the strength of an earthquake

triangulation

process used to locate the epicenter of an earthquake

Richter scale

scale of magnitude based on the size of seismic waves produced by an earthquake

Mercalli intensity scale

scale that measures the effects or severity of an earthquake

Match the earthquake measuring instrument with its correct description.

seismograph measures strength of an earthquake; measurement is based on the size of seismic waves 2 measures strength of larger earthquakes; measurement is based on multiple variables 3 measures effects of an earthquake; measurement can vary from place to place