Module 5 Flashcards
Stereonet
great circle
point
Types of stress
Compression (reverse fault)
Shear (strike slip)
Tension (normal fault)
Borehole shows repeating stratigraphy
Could be a reverse fault (strat pushed up over itself)
Borehole shows some strata has mysteriously disappeared.
Normal fault
What are earthquakes and why are they useful
Earthquake- a train of elastic waves past a given location
Useful because the waves allow us to observe properties of the earth’s internal structure (IE density).
These waves are generated when elastic strain is released as a fault ruptures.
In the context of a wedge failure, describe how its analyzed and what a geologist is looking for.
Using a stereonet, slope is plotted, as well as the planes of the two cuts made by the workers. The intersection of the two cut planes determines the direction the wedge will go down the slope. A geologist makes sure the slope of the cuts is more gradual than the original slope. This is so that it doesnt immediately fall upon being cut. You can tell because the more gradual slope will be closer to the perimeter of the middle circle.
Earthquake terminology
Focus/Hypocenter: Exact point where elastic strain released
Epicenter: Point on Earth’s surface above Focus
Magnitude: Energy released by the elastic strain. Defined by Richter scale (IE 6.5 or 7) Going up by 1 indicates a 30 fold increase in energy.
Types of earthquakes by depth, What continent boundary
Deep is 700>x>300 km convergent/compressional
Intermediate is 300>x>70km convergent/compressional
Shallow is 70>x>0km convergent/divergent/transform
Types of seismic waves, list them, what distinguishes them
Body waves
P waves-Fast like a Porsche, these 1st to arrive waves Push and pull whatever it goes through like a slinky. hard to feel as a human. These speedy waves go through water! Think P=precipitation likey
S waves- Slow like Saturn, these waves arrive second and behave like a whip you crack. As the wave travels down the whip, the whip goes up and down, PERPENDICULAR to the vector or propogation. Water has no shear force, and thus these do not go through fluids. Think water says Stop to S waves
Surface waves
R or Rayleigh waves- rolling circular waves, make you dizzy. Racecar goes in circles? or R=Rolling circular waves
L or Love waves-Scary, building toppler waves. Shift ground left and right. Slow like a lumbering giant
How can you generally tell distance from location to epicenter
P is faster than S, bigger gap in time between waves means farther distance.
How many different location data we need to find epicenter? Focus?
3 for Epicenter, 4 for Focus. Draw circles where radius is distance from station determined by relative arrival time of P and S waves.
How to define Magnitude, Intensity of an earthquake
Magnitude: Energy released by the elastic strain. Defined by Richter or Moment Magnitude scale (IE 6.5 or 7) Going up by 1 indicates a 30 fold increase in energy.
Intensity: Using Mercalli scale, it defines relative damage done by the seismic waves for the purpose of delegation of relief efforts. Value goes up with destruction. Highest values are found near epicenter in ROMAN NUMERALS (IX near epicenter, II far away)
This value is determined by peak horizantal acceleration of a building, which is determined by sensors in the basement.
Attenuation and Amplification; Under what conditions are the seismic waves amplified as they travel
Attenuation of seismic waves is the tendency to go down in energy and amplitude as they travel.
Amplification of waves can occur if it encounters soft or unconsolidated material.
What did Inge Lehman discover and how.
Inge was recording seismic waves from earthquakes around the world and noticed she only recieved P waves from earthquakes on the other side of the planet. She postulated that the core must be liquid or the S waves would be able to go through.
Layers of Earth
Crust
Lithosphere-crust and upper mantle
Asthenosphere-partially melted, causes plates to move
