EARTHQUAKES Flashcards
what does Seismicity (earthquake activity) occur due to
= Motion along a newly formed crustal fracture (fault)
= Motion on an existing fault
whats the amount of movement along a fault called
displacement (i.e., offset or slip)
The spot within the Earth where earthquake waves originate
Hypocenter (focus)
* Epicenter = land surface above it
how are faults structured
Most faults slope (although some are vertical)
- Footwall = block below the fault
- Hanging wall = block above the fault
5 Fault Types and what its based on
based on relative block motion
- Normal fault = hanging wall goes down relative to footwall
- Reverse fault = hanging wall goes up relative to footwall - steep slope
- Thrust fault = Special kind of reverse fault - not steep slope
- Strike-slip fault - no vertical motion - one fault slides sideways past other
- Oblique-slip fault (most faults) - hanging wall slips diagonally
whats a Fault scarp
ground rupture
whats the Fault Initiation (Elastic rebound theory )
< Tectonic forces add stress to unbroken rocks.
< The rock deforms slightly (elastic strain).
< Continued stress will cause growth of cracks.
< Eventually, cracks grow to the point of failure.
< When the rock breaks, elastic strain transforms into
brittle deformation, releasing earthquake energy
how do faults move
in jumps -> stick-slip behavior
= Stick – Friction prevents motion
= Slip – Friction briefly overwhelmed by motion
How does faulting generate earthquakes
When rocks break, stored elastic strain is released
what may result due to faulting
uplift or subsidence.
= measureable using InSAR
2 types of seismic waves
- Body waves – Pass through Earth’s interior
- P waves = Compressional / Primary waves, Push-pull (compress and expand) motion, Travel through solids, liquids, and gases, Fastest
- S waves - Shear / Secondary waves, “Shaking” motion, cannot travel through liquids, Slower - Surface waves – Travel along Earth’s surface (slowest and most destructive)
- L-waves (Love waves) = Move back and forth like a writhing snake
- R-waves (Rayleigh waves) = Move like ripples on a pond
seismic wave speed through different substances
- Fastest through solid igneous rock
- slower through sedimentary rock
- slowest through a liquid
what 2 things do seismographs measure
= Wave arrival times
= Magnitude of ground motion
Two means of describing earthquake size
= Intensity - degree of shaking based on damage (Roman numerals assigned to different levels of damage)
= Magnitude - amount of energy released - max amplitude from seismograph (scales are logarithmic)
plate boundaries that emit Shallow and Intermediate / deep earthquakes
= Shallow – Divergent, transform, & convergent
boundaries
= Intermediate and deep – Convergent boundaries
Shallow earthquake characteristics
0-20 km
= Along the mid-ocean ridge
= Transform boundaries
= Shallow part of trenches
= Continental crust
Intermediate / deep earthquake characteristics
20-300 km / 300-670 km
- occur in the Wadati-Benioff zone
what are Continental Earthquakes
Earthquakes in continental crust
= Continental transform faults (San Andreas, Alpine).
= Continental rifts (Basin and Range, East African Rift).
= Collision zones (Himalayas, Alps).
= Intraplate settings (ancient crustal weaknesses)
whats the San Andreas Fault
The Pacific plate meets the North American plate
< A very active strike-slip fault
what are Intraplate Earthquakes
not near plate boundaries (<5%)
< Not well understood
what kind of motion do the different waves cause
- P-waves (1st to arrive) - rapid up-and-down motion
- S-waves (2nd to arrive) - stronger back-and-forth motion
- Surface waves (L waves) - Ground writhes like a snake
- Surface waves (R waves - last to arrive) - land surface moves like ripples in a pond + very big damage
how does The nature of the subsurface material effect the Severity of shaking and damage caused by earthquakes
- Bedrock transmits waves quickly = less damage
- Sediments bounce waves = amplified damage
what is Liquefaction effect from earthquakes
Water-saturated sediments turn into a mobile fluid (quicksand)
- Land will slump and flow.
- Buildings may founder and topple over
what are tsunamis
long-wavelength (low wave height) shock waves generated by sudden changes in sea floor level in coastal areas
- caused by earthquakes, ocean landslides, or volcanic eruptions
