Name Date Period

Earth Systems-Seismology and Earthquake Hazards

Seismometers and Seismograms

Most of the vibrations caused by seismic waves

cannot be felt at great distances from an earthquake’s epicenter.

However, they can be detected by sensitive instruments

called, which measure

horizontal or vertical motion during an earthquake.

The record produced by a seismometer that can

provide individual tracking of each type of

seismic wave is a .

Travel-time curves provide the average time it

takes for to reach seismic stations.

The Richter Scale

A numerical rating system that measures of an earthquake.

 is the measure of the released during an earthquake.

The numbers in the Richter scale are determined by the height, called the , of the largest seismic wave.

Moment Magnitude Scale

The moment magnitude scale is a rating scale of the energy released by an earthquake, taking into account the , the amount of , and the rocks’ .

Depth of Focus

Earthquakes are classified as , , or , depending on the location of the focus.

Shallow-focus earthquakes are the .

Locating an Earthquake

The epicenter’s location, as well as the time of occurrence, can be determined using and .

Distance to an Earthquake

Seismologists determine the distance to an earthquake’s

epicenter by measuring the on any seismogram

and identifying that same time

on the travel-time graph.

To locate the epicenter of an earthquake, scientists identify

the on a map, and draw a

circle with the to the epicenter

from each station. The point where all the circles intersect

is the .

Seismic Belts

The majority of the world’s earthquakes occur along narrow that separate large regions with little or no seismic activity. The locations of most earthquakes correspond closely with .

Earthquake Hazards

Earthquake hazards are factors that determine the severity of damage produced by an earthquake.

Identifying earthquake hazards in an area can sometimes help to prevent some of the damage and loss of life.

Structural Failure

  • shaking causes a building’s supporting walls to collapse and the upper floors to fall one on top of the other like a stack of pancakes

Land and Soil Hazards

In sloping areas, earthquakes can trigger .

In areas with sand that is nearly saturated with water, seismic vibrations can cause the ground to behave like a in a phenomenon called .

Tsunami

A tsunami is a large ocean

generated by

of the seafloor during an earthquake.

Earthquake Forecasting

The probability of an earthquake’s occurrence is based on two factors:

Seismic Risk

  • The probability of earthquakes in is much greater than elsewhere on Earth.
  • The history of an area’s seismic activity can be used to generate .

Recurrence Rates

  • Earthquake-recurrence rates along a fault can indicate whether the fault ruptures at intervals to generate similar .

Seismic Gaps

  • Seismic gaps are sections located along faults that are known to be active, but which have not experienced for a long period of time.