Locating EQs pp 217-221

1. What is a seismograph? How does it work?

2. What are seismic waves

3. How do you “read” a seismogram?What info. can it give you?

4. How many seismic stations’ data do you need to locate an earthquake?

Earthquake Seismic waves

2 Types;

Body waves

http://www.youtube.com/watch?v=yOGoKCK17a4

Surface waves

Velocity of P and S waves are different with depth and material

Asthenosphere

Mantle

Outer core

Inner core

http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page03.cfm

Body Waves (pg 215)travel __________________ the earth

Primary (P) waves Secondary (S) waves

Compression waves, push, pressure

Changes the density, volume of rock as it passes through.

Pass thru solid, (molten), liquids, gas

Arrives first, fastest ≈6 km/s

* (depends on the density of rock – faster in more dense material)

Transverse, “S” snake, side-to-side

Changes the shape of rock as it passes through.

Passes through Solids only

Arrives second, slower ≈3.5 km/s

* Is more destructive

P waves compress the rock’s volume as it travels

S waves change the shape of the rock up and down

Earthquake waves

2 Types;

Body waves

Surface waves

Surface Waves (page 216)

• Love Waves

• Rayleigh Waves

http://www.geo.mtu.edu/UPSeis/images/Love_animation.gif

http://www.geo.mtu.edu/UPSeis/images/Rayleigh_animation.gif

Surface waves travel along the surface, tossing structures up.

On a seismograph, what part is stationary?

What part moves?

(Body waves)

(1). On April 23, 2000, a magnitude 6.9 (Mw) earthquake occurred at 09:27:23.1 (UTC*) approximately 600 km below Santiago del Estero Province, Argentina (2). The fastest-traveling seismic waves (P-waves) traveled through the earth's mantle and arrived at a station near Parkfield, CA about 11 minutes later, at 09:38:55 (3). The slower-traveling S-waves also travelled through the mantle, and reached Parkfield 21 minutes after the earthquake occurred. (4). An aftershock wave that arrive approximately 19 min. later.

After shock

4

Compare how…

the arrival times of P waves and S waves at a seismic station

are like…

the time difference between a flash of lightning and hearing the thunder.

How FAR AWAY is the storm?

An Analogy

Station 1

Station 2

Which station was CLOSEST to the epicenter of the earthquake?

HOW FAR away was the earthquake?

3.5 minutes away!

Yes, but HOW FAR is that?

The time interval between the arrival of the P-wave and the S-wave is

3.5 min the distance to the earthquake epicenter is __________ miles

How far away is the EQ epicenter

if the P and S waves

were 5 minutes apart?

Data from one GPS satellites can locate you within a large area!

Data from two GPS satellites can narrow your location

Data from three GPS satellites can pinpoint location within a few feet!

Triangulation

Data from THREE stations is required to locate an earthquake

CA

B

Triangulation

USGS Earthquake activity last 7 days

New Madrid Fault zone

Illinois has many faults and

fractures, most in southern Illinois

New Madrid Fault Zone

Under the sedimentary rock strata lies a series of ancient faults that shift and settle causing earthquakes