Presentation on theme: "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?"— Presentation transcript:
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?
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) wavesSecondary (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
1. Earthquakes release ___________! 2. MOST EQ’s are caused by...... 3. A fault is… 4. ___________ prevents the plates from moving. 5. The elastic rebound theory states that plates… 6. Where is the focus of an earthquake? 7. Where is the epicenter of an earthquake? Bell work
(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. station 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?
What is time difference between the arrival time of the P wave and the arrival of the S wave? ______sec. 36
How far away is that???? Distance = time x speed ???? = 36 sec x 6 km/s Distance = But in what direction???? 216 km away
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