Before you jump into this slide show,
you should view the Presentation on
Plate Tectonics and Earthquakes
See notes for link.
Part 2: Earthquake Seismology
This PowerPoint presentation provides an Introduction to
Earthquake Seismology. Teachers are encouraged to use this
presentation for their own learning and/or adapt the
presentation for classroom use. This PowerPoint presentation can
be used in conjunction with the PlateTectonics&EQsGuide, a PDF
that provides a logical outline of this PowerPoint and its
companion Plate Tectonics PowerPoint.
• Underlined orange text indicates a link to a teaching resource
on the TOTLE web site. When you view the PowerPoint
presentation in “Slide Show” view, you can click on the underlined
orange text to send your web browser to the linked web page.
• “Normal” view in PowerPoint includes a notes panel below each
slide. Background information, links to computer animations, video
lectures, lesson plans, classroom activities, and lots of teaching
tips are contained in the notes.
• We recommend that you first view this presentation in Slide
Show view then return to slide #1 and step through the
presentation in Normal view to examine the notes.
Epicenter & Focus of Earthquakes
Epicenter:
Location on Earth’s surface directly above the earthquake.
Focus (or hypocenter):
Location within the Earth where the earthquake occurred.
Watch video lecture “Earthquake focus (hypocenter) and epicenter”
Why are there earthquakes?
Brittle vs. ductile
Example:
Subduction-zone
earthquakes
occur in discrete
areas within and
between plates.
Why?
Watch video lectures
“Lithospheric plates”
“Brittle fracture”
& “Brittle and ductile deformation”
Why are there earthquakes?
Brittle vs. ductile
Body Waves and Surface Waves
Surface waves
travel along
Earth’s surface.
Body waves
(P and S) travel
inside Earth.
Activity:
“SeismicWaves Program”
see notes.
While P- and S- waves radiate outward in all directions, surface waves travel
along the surface of the Earth and decrease in amplitude with depth.
Watch video lecture
“Kinds of seismic waves”
Types of seismic waves
P wave
S wave
Surface
waves
Fast
Intermediate
Slow
Watch video lecture
“P, S and surface waves”
Body waves
P waves are compressional
Link to animation in Notes panel.
Activity: “Seismic Waves and the
Slinky”; see notes.
Body waves
S waves are shear waves
Link to animation in Notes panel.
How can lines of students model P-wave
and S-wave propagation in the classroom?
See Activity on John Lahr’s web site.
Link provided in Notes panel.
Surface waves
Rayleigh & Love Waves
Link to Rayleigh-wave motion animation provided in Notes panel.
Link to Love-wave motion animation provided in Notes panel.
How do scientists detect earthquakes?
When an earthquake occurs the seismic waves travel through the Earth to the
seismic station where the information is transmitted to distant computers.
A seismograph detects
and records EQs.
A seismogram is the
EQ record.
Seismometers
Watch a computer animation of a
vertical seismometer recording
arrivals of the P and S waves.
Link to Vertical Seismometer animation in Notes.
Watch an actual seismogram being
recorded during an earthquake.
Link to Real Seismogram video in Notes.
Ray Paths and Travel Times
Link to “Ray Paths & Travel Times” animation in Notes.
Seismic waves traveling from a distant earthquake to a
seismic station. P & S waves travel through Earth’s
interior while surface waves travel through the
lithosphere near the surface.
Ray Paths and Travel Times
Link to “Seismic Waves to Four Stations” animation in Notes.
Watch seismic waves traveling from a distant earthquake
to four seismic stations (and the seismic cow).
Seismic Wave Travel Time Curves
Link to “Travel-Time Curves” animation in Notes.
By analyzing earthquake waves from thousands
of earthquakes, seismologists have determined
the travel times for seismic waves.
How far away was the earthquake?
Use S-arrival time minus P-arrival time to determine
distance from the travel-time curves.
Watch video lecture
“Determine the Distance”
ACTIVITY:
Locating an Earthquake
1
1)
Determine distance of EQ
from three seismic stations
by calculating the S minus P
arrival times.
2) Plot them on the traveltime graph.
3) Intersection of the circles
gives the location.
3
2
World Seismicity & Plate Tectonics
Modified from USGS Graphics
ACTIVITY: See Notes for a link to a classroom
activity on world seismicity, volcanoes, and plates.
INTERNET ACTIVITY: Look at current earthquakes
For an up-to-the-minute world
map of earthquakes, check out
the Seismic Monitor on the
IRIS web site.
See notes for link.
To see seismic data from
stations near you, go to the
USArray Station Monitor
and enter your zip code.
See notes for link.
How big was it? The Richter Scale
What is the Richter
magnitude of this EQ?
S — P = 26 sec
Amplitude
= 23mm
Magnitude = 5
Magnitudes and Energy of Earthquakes
Annual Numbers of EQs
What’s the message?
MOST of the energy is released by around 20
magnitude 7 and larger earthquakes every year.
The Earthquake Machine
Think forces, faults, and friction!
Stick-slip motions on faults
produce earthquakes.
Activity:
“Earthquake Machine” see notes.
Link to EQ Machine animation in Notes.
Wood blocks, sandpaper, and
rubber bands, can model the
slow storage and rapid
release of elastic energy.
Can We Predict Earthquakes?
Earthquake prediction eludes us. The Earthquake Machine experiment shows
that the interplay of forces, faults, and friction is complex and “unpredictable”.
However, if rocks on opposite sides of a fault are moving, elastic energy is being
stored and will eventually be released in an earthquake. If we determine the
past history of earthquakes on a particular fault, we can forecast the
probabilities of earthquakes occurring on segments of that fault. Earthquake
forecasting is valuable because this tells us where we must construct
earthquake-resistant buildings, highways, and bridges.
To learn about earthquake
hazards, damage, and mitigation,
view the PowerPoint slide show
on Earthquake Hazards.
See notes for link.