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
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
(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