1: Earthquakes Flashcards
Divergent Tectonic Settings
Tensile (pull-apart) stress produces normal faults.
Convergent Tectonic Settings
Compressional Stress produces reverse (thrust) faults.
Transform Tectonic Settings
Sheer stress produces strike-slip faults (sliding pass each other)
Surface rupture
Forms fault scarp - amount of slip on fault
Epicenter
Point on surface above focus
Focus
When rupture on fault plane started
Body Waves
Travel through the interior of the Earth in all directions from the focus. Includes P and S waves.
P-Waves
- Primary
- Fastest wave (4-6 km/sec in hard rock)
- Compressional
- How the waves are transmitted
- Push-Pull like a slinky
S-Waves
- Secondary
- 2/3 the velocity of P-waves
- Shear (S stands for)
- Not push-pull, more shear
- Cannot travel through the outer core.
Surface Waves
- Travel on the surface of the Earth outward from the epicenter
- Slower than body waves
- Traveling through harder/less dense things
- responsible for damage to structures
- Body waves don’t do a lot of damage.
Rayleigh (R) Waves
- Elliptical up and down motion (like water ripples)
Love Waves
Horizontal side to side motion (snake up your body)
Amplification of Surface Waves
Waves slow down from high density to low density material resulting in increased amplification.
Mercalli Intensity Scale
- measures intensity of ground shaking (I-XII)
- based on type of damage and accounts of observers
- Ex. Chicago feels it harder because it is on softer sedimentary rock, while W. Virginia is on hard rock and feels it less.
Richter magnitude
- Determined from seismograph measurements
- a better measure of the size of the earthquake at the focus (instead of somewhere further away) based on
- The largest body wave amplification (usually the S-wave) measured at the seismometer.
- Distance the seismometer is from the epicenter
Locating the epicenter of an earthquake
- The further you are from the epicenter the further the p-wave will be from the s-wave.
- They create a circle around the station based on the P/S-wave lag time. - Keep doing this at multiple stations until you get a sole intersection of your circles between them all.
Seismic hazards
- shaking and ground rupture
- liquefaction
- landslides
- fires
- disease
- tsunami
Earthquake prediction (short term)
- sometimes earthquakes are preceded by natural precursors such as foreshocks, low-frequency radio waves, weird animal behavior, etc
Earthquake prediction (long term)
- Involves the assessment of the probability of an earthquake of a certain magnitude occuring along a particular fault over a period of time.
Long Term: different segments of ___ may have different levels of _____ based on previous history of____
fault; hazard; movement
recent movement = lower hazard
% of being hit if living in cali?
62%
