Earthquakes Flashcards
What is a fault?
Rupture in Earth’s crust along which rocks on one side move past those on the other.
What are the three primary types of fault?
Strike slip: plates move up/down (horizontally) from one another (transform).
Normal: plates pull apart (divergent).
Reverse: hanging wall moves over footwall (convergent).
What are two, more minor types of faulting?
Thrust: lower angle reverse fault (<45 degrees).
Blind thrust: occurs underground, ductile rock layers fold, go largely unnoticed.
The horizontal line on the dipping surface is what?
Strike.
What is stress and strain, pertaining to rocks?
Stress: forces applied on rock.
Strain: change in shape of rock in response to stress.
Typical rocks deform _____.
Elastically.
Opposite sides of faults are typically deformed instead of moving. Movement occurs along the fault when rocks undergo what?
Brittle failure.
Rock mass fails suddenly by faulting when what force occurs?
Shear stress > shear strength.
What are three elements of earthquakes in divergent margins (normal faults)?
Common, low magnitude, shallow focus.
What is perhaps the most notable transform boundary?
San Andreas fault system.
Earthquakes in transform boundaries tend to be what two things?
High magnitude, shallow focus.
Convergent boundaries are caused by what kind of motion and consist of what type of faulting?
Horizontal motion.
Reverse faults.
Earthquakes in convergent boundaries tend to be what two things?
Shallow to deep focus, large magnitude.
What are seismic waves?
Energy released from the fault slip traveling outward.
Define the focus (hypocentre) and the epicentre.
Focus (hypocentre): location of movement along the fault.
Epicentre: point on the map directly above the focus.
Describe primary waves (P-waves) in terms of wave style, speed, and where they can travel.
Compressional (succession of elastic compressions/expansions).
Fastest (4-7 km/sec in bedrock).
Travel through all materials.
Describe secondary waves (S-waves) in terms of wave style, speed, and where they can travel.
Shear waves (succession of transverse vibration).
Arrive after P-waves (2-5 km/sec in bedrock).
Only travels through solids.
Rayleigh and Love waves are what? What are they triggered by, and what is their speed?
Series of violent vibrations on surface.
Triggered by P-waves reaching surface.
Velocity ~90% of S-waves.
Seismic waves _____ like light.
Refract.
Is the Richter Scale commonly used? How is it determined and how is each level stronger than the other?
Not commonly used except in local small earthquakes.
Determined from logarithm of the amplitude of waves recorded by seismograph.
Each level 10 times stronger than previous level.
The Moment Magnitude Scale estimates what? How is it calculated into a magnitude?
Estimates the total energy released by an earthquake.
Calculated from area of fault and distance the ground moved along fault, derived from analysis of all waveforms recorded from shaking. Seismic moment computed, converted to a magnitude.
The seismic moment is a measure of the size of an earthquake based on what three things?
Area of fault rupture.
Average amount of slip.
Force required to overcome the friction sticking the rocks together that were offset by faulting.
For dip slip faults, what will seismographs feel?
Depending on location from focus sphere, some will feel “push” from focus, others initial “pull” towards.
The Mercalli Intensity Scale is determined by damage done to structures. What is it dependent on, and what is the damage in question related to?
Depends on distance from fault rupture.
Related to crustal rocks.
