Chapter 8: Earthquakes and Earth's Interior Flashcards
What is an Earthquake?
ground shaking caused by a rapid release of energy inside the Earth due to tectonic stresses that cause rocks to break suddenly along fault lines
When a fault slips, energy is released and travels outwards causing what?
A seismic wave
EX: waves created when a pebble is dropped into a pond
What is a a Focus of a seismic wave?
The point inside the Earth on fault where earthquakes are originated
What is a Epicenter of a seismic wave?
The point on the Earth’s surface that is directly above the Focus
Types of Earthquake faults
Normal fault (downward)
Reverse fault (upward)
Left-lateral fault
Right-lateral fault
Foot wall &
Hanging wall
Foot wall– the part of the fault you can climb up.
Hanging wall– the part of the fault that looks like it is “hooked” onto the foot wall.
Earthquake in Port-au-Prince, Haiti
a) Magnitude of 7.0
b) killing 24% of population
c) left-lateral strike-slip fault
d) 4:53 pm, Jan. 12, 2010
e) 52 aftershocks
Great San Francisco Earthquake
a) 7. 8 magnitude
b) April 18, 1906
c) problem– fires breaking out from candles/stoves knocking ove
What geology professor headed the commission at UC- Berkeley?
Andrew Lawson
Elastic Rebound Theory
bent rocks straightened with a sudden snap.
EX: rubber band or a a yard stick being bent or stretched.
(San Andreas Fault of 1906)
Causes of Earthquakes:
Stress
the force imposed on a rock
Causes of Earthquakes:
Strain
a change in the shape of a rock, in response to the stress it is undergoing.
Rocks under low stress cause what?
Deform elastically under low stress.
Revert to former shape when stress is removed
Rocks under high stress cause what?
Deform plastically under high stress.
Permanently change shape of flow
What is a fault?
fractures in the crust along which rocks on one side move past rocks on the either side; this movement can be either vertical or horizontal.
Faults are mostly located where?
along the plate boundaries.
Types of Earthquake waves
Body waves
p-wave s-wave
Surface waves
l-wave r-wave
What is a body wave and it’s secondary waves?
They travel through the body of the earth.
Primary wave- compressional motion (push-pull) feels like a sudden jolt. EX: slinky
Secondary wave- Shear motion (side to side). More destructive than P-waves.
What is a surface wave?
they only travel along the surface, NOT through the Earth
What waves are the slowest and most destructive?
Love waves (back and fourth) Rayleigh waves (ripples on a pond)
What is a Seismograph?
They record the ground shaking of the earthquake waves on a seismograph
How do we locate earthquakes?
- Use the time interval between p-wave and s-wave.
- Arrival time of p-waves and s-waves indicate distance, NOT direction of the Earthquake.
- Wave arrival time needed from at least 3 stations to pinpoint location of earthquake use for triangulation of epicenter.
Modified Mercalli Intensity Scale
Reflects the subjective observations of how strongly people feel shaking and the severity of damage.
- Strongest happening: near the epicenter OR where ground conditions favor strong ground shaking.
What earthquake was the first one to be seen on live television?
Loma Prieta Earthquake, 1989 (6.9) at the world series game
Richter Magnitude Scale was based on what?
the maximum amplitude of earthquake waves measured on a seismograph.
Intraplate Earthquakes are those that occur when?
Within the tectonic plates, not at the tectonic plate boundaries.
The Reelfoot Rift
was a failed rift zone that has since filled in with Mississippi River embayment sediments so faults along the New Madrid are deeply buried.
Secondary ground effects from earthquakes often trigger and cause what?
Landslides and Liquefaction
Secondary ground effects from Earthquakes: Tsunami
Japanese name for harbor wave; also called a ‘seismic sea wave’
(sometimes called tidal waves, not not related to tides)
How are Tsunami’s created?
By Earthquakes when a slab of the ocean floor is suddenly thrust upwards along the fault line.
(They can also be caused by large landslides)
A Thrust or Reverse fault causes the ocean floor to do what?
Causes the overlaying water to suddenly shift upwards and outwards.
Subduction Zones are what type of boundary?
They are the most dangerous and damaging.
Earthquakes and faults are associated with what?
Plate boundries
The Indian Ocean Tsunami
Swept Away tourists in Phuket, Thailand
Dec. 26, 2004.
Less than 2 hrs after EQ, a giant wave surged inland
Riprap
Works by absorbing and deflecting the energy of waves before they reach the defended structure.
Pacific Ocean Tsunami
March 11, 2011 (9.0)
Coast of Japan
10-meter high waves
Wave attack within 10 min of EQ
Types of damage earthquakes cause…
Structures breaking
Tsunamis
What is Seismic Retrofitting?
The X structure on building that allows the building to be more stable.
Trans-Alaskan oil Pipeline
prevent damage from and EQ’s shaking by putting the pipeline of rollers.
Built on Denali Transform Fault
Travel times of P-waves and S-waves vary through Earth depending on?
the properties of the materials though which the waves are traveling
S-waves travel only through solids because?
It is the primary indicator that the outer core is liquid since the S-waves will not travel through this layer
P-waves travel though both solid and liquid but?
they refract as they go though liquid
Shadow zones
Absence of p-waves from 105 degrees to 140 degrees around the globe after an EQ
Absence of S-waves from 105 degrees to 105 degrees around the globe.
