The Earth's Interior Flashcards
What is the Richter Scale?
Developed to quantify and compare earthquake magnitudes. Logarithmic
What is the P-S time interval, and what can it be used for?
The difference in arrival time between P and S waves. Used to ascertain distance between seismometer and epicenter
How much faster are P-waves to S-waves?
About twice as fast
What two things on the printout of a seismometer are used to determine the magnitude of the earthquake?
- the maximum amplitude
2. The P-S interval (used to determine distance from epicenter).
What is needed to determine the geographical location of the epicenter?
Multiple seismometer stations to triangulate.
Why do seismic waves increase in velocity as they travel through the earth?
Velocity of seismic waves increases with the rigidity of a solid, and the middle of the earth is more dense.
What is rigidity
A measure of how difficult a solid is to shear
How can S-waves travel faster through solids?
The solids must have higher shear moduli
What kind of solids can S-waves move through faster?
Solids with higher bulk moduli and shear moduli
What is the line of travel of an earthquake wave called?
ray path
What causes curved ray paths?
Refraction
What is refraction?
The tendency for seismic waves to bend as they change in velocity and/or encounter varying densities of matter
Where are the S-wave shadow zones?
The opposite 3/8 of the earths surface?
Where are the R-wave shadow zones, if the earthquake is at 12 o’clock?
8 and 4
How can we know that the outer core is liquid?
P-waves traveling through the slower liquid core are refracted inwards, causing two shadow zones.
How can we know that the inner core is solid?
weak, late P-waves were detected in the shadow zones, meaning they were refracted off something solid
What is the Gutenberg discontinuity?
significant change in seismic waves at the core-mantle boundary
What is the Lehman discontinuity?
significant velocity increase at the inner core boundary
Define the moho discontinuity?
The boundary between the crust and the mantle
How was the Moho discovered?
Two different versions of the same seismic wave would arrive at different times. This is caused by some waves moving faster through the mantle than waves movign through the less-dense crust
What generates Earths magnetic field?
movement of the rotating, convecting, electrically conducting outer core
Explain how a seismometer works
A heavy weight is hung from a support, and the weight bears a pen that writes on paper. As seismic waves move past the mechanism, the earth moves, while the ball and pen stay put, creating lines indicative of the different waves.
What information from a seismogram printout does one need to calculate the
distance from that seismogram to an earthquake epicentre?
The P-S interval.
Can the location of an earthquake be determined from a single seismogram
printout?
only if two or more seismogram printouts are available from other locations.
What does one require from a seismogram printout to plot the magnitude of an
earthquake on the Richter scale?
The maximum amplitude of the seismic waves and the P-S interval
What evidence exists for the Gutenberg Discontinuity?
The S-wave shadow zone.
What evidence exists for the Lehmann Discontinuity
Weak, indirect P-waves are observed in the P-wave shadow zone
What evidence exists for the Moho Discontinuity?
P- and S-waves speed up at depths where the mantle reaches the crust.
How deep is the earths crust on average?
15-20km on continental, 5-7 on oceanic
