5-2 F
Objectives:
Compare and contrast primary, secondary and
surface waves.
Explain how an earthquake epicenter is located
using seismic wave information.
Describe how seismic wave studies indicate the
structure of Earth’s interior.
The energy that is produced by the rock breaking
creates waves of energy known as seismic
waves. They travel outward for the earthquake
focus.
An earthquake begins when rock that is under
pressure brakes. This point is know as the focus.
The spot on the
Earth’s surface
directly above the
focus is known as the
epicenter.
The fist of the seismic waves is known as primary
waves. These waves compress and expand like an
accordion. They can move through solids and
liquids.
After the primary waves come, secondary waves
develop. These waves vibrate side to sides and
up and down. They shake the ground back and
forth. Secondary waves can only move through
solids.
Energy that reaches the surface of Earth
generates waves that travel outward for the
epicenter. Surface waves move more slowly than
P-waves and S- waves, but they cause most of the
destruction during an earthquake.
A seismograph is an instrument used to record
small movements of the ground. In order to locate
an earthquakes epicenter, you need three
seismograph stations. Each location is circled and
the points at which the circles meet is the
epicenter.
Scientists have used seismic wave information to
map the Earth’s structure. Waves speed up or slow
down based on the density of the material that it
goes through.
This bending and stopping
of waves creates a shadow
zone where not seismic
waves are detected.
The inner core- iron, nickel (solid)
The outer core- iron, nickel (liquid)
Mantel- largest layer, silicon, oxygen, iron &
magnesium.
Crust- is made up of rock and soil. It is separated
from the mantel by the Moho discontinuity.
The seismic waves that are triggered by an
earthquake are measured by the Richter scale.
Less than 3.5 Generally not felt, but recorded.
3.5-5.4 Often felt, but rarely causes damage.
Under 6.0 At most slight damage to well-designed buildings. Can
cause major damage to poorly constructed buildings over small
regions.
6.1-6.9 Can be destructive in areas up to about 100 kilometers
across where people live.
7.0-7.9 Major earthquake. Can cause serious damage over larger
areas.
8 or greater -Great earthquake. Can cause serious damage in
areas several hundred kilometers across.