2. Long period instruments: T 20 seconds (surface waves).
3. Broadband instruments: Both long and short period (T).
B. Seismogram Compoments.
1. Vertical (Up and Down motion).
2. Horizontal (1 for East and West motion) (1 for North and South motion).
C. Local Seismograms.
1. All three components do not have time to seperatre.
D. Teleseismic Seismograms.
1. Greater than 100 km away.
2. Up, east, and north are easily defined.
E. Teleseism.
1. S waves have the largest amplitude.
2. Body waves spread and travel as a sphere.
3. Surface waves spread and travel as a cylinder.
4. Body waves lose energy faster because they have shorter periods than surfaces waves and earth attenuates high frequency (short period) waves faster.
F. Seismic Phases.
1. P, S, PP, SP, PcP, PKP, PKKP, PKIKP, PKJKP, etc.
2. c = Reflection off of core mantle boundary.
3. k = P wave through outer core.
4. I = P wave through inner core.
5. J = S wave through inner core.
6. i = Reflection off of the outer core/inner core boundary.
7. pP = P wave directed up to the surface and reflected back down as a P wave.
8. PKJKP = S wave through inner core.
9. PKIKP = P wave through inner core.
G. Shadow Zones.
1. The spreading of waves caused by the outer core bends wave paths creating a "shadow" where no waves are recorded.
2. Outer core is liquid because S waves created a shadow zone.
3. PKJKP proves inner core is solid.
H. Travel Time Plots.
1. Waves converge with distance from the earthquake.
III. Seismic Instrumentation.
A. Seismograph Components.
1. Clock: Needs accurate clock to tell when seismic waves arrive.
a. Uses radio broadcasts or GPS signals.
2. Amplifier.
a. We can adjust this to maximize signal to form two frequency bands.
b. High Frequency: Short period, T = 1 sec = Body waves.
c. Low Frequency: Long period, T = 20 sec = Surface waves.
3. Recorder/Telemetry.
4. Seismometer.
B. Seismometer.
1. Inertial Mass: Relative motion of magnet in coil produces an electric signal. .
2. Resonant Frequency: Only records waves of a certain frequency.
