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lesson 4: earthquakes

Terms in this set (42)

Earthquake
a vibration of the earth produced by the rapid release of energy
Focus (hypocenter)
the source of an earthquake. energy radiates in all directions from the focus.
Epicenter
location of the focus projected on the earth's surface
Elastic Rebound Theory
rocks on both sides of an existing fault are deformed by tectonic forces. rocks bend and store elastic energy. frictional resistance holding rocks together is overcome.
Seismograph
instruments that record seismic waves. records the movement of earth relative to a stationary mass. shaking of earth produces waves on a rotating drum or magnetic tape.
Types of Seismic Waves
body Waves
surface Waves
Body Waves
waves that move through the interior of the earth.
primary (p-waves) - compressional
secondary (s-waves) - shear
Surface Waves
rayleigh waves - rolls across the ground like ocean waves, usually much larger than other waves. most shaking felt is from a rayleigh wave
love waves - fastest surface wave, moves the ground from side to side
Fault
a large fracture on which sliding occurs
mercalli intensity
A scale that measures the intensity of an earthquake. It quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures on a scale of I through XII, with I denoting not felt and XII total destruction. The values will differ based on the distance to the earthquake, with the highest intensities being around the epicentral area
richter magnitude
a logarithmic measure of how much the ground moved at the seismograph as seismic waves pass by
San Andreas Fault
large fault in California, prone to earth quakes
Short Range Predictions
goal is to provide a warning of the location and magnitude of a earth quake in a narrow time frame. research concentrated on monitoring possible precursors. measure uplift, subsidence and strain in the rock.
Long Range Forecasts
gives the probability of a certain earthquake magnitude occuring in 30-100 years, based on the premise that earthquakes are what repetitive or cyclical
Earthquake intensity
a measure of the degree or intensity of the earthquake shaking at a given location based on the amount of damage
Earthquake magnitude
estimates the amount of energy released at the source of the earthquake
Modified Mercalli Intensity Scale
was developed using california buildings as its standard. the drawback to this is that destruction may not be a true measurement of energy released
Richter Scale
based on amplitude of largest seismic wave recording, accounts for the decrease in wave amplitude with increased distance.
Structural Damage Attributable to:
- intensity and duration of vibrations
- nature of material on which a structure rests
- design of structure
Tsunami (Seismic Sea Waves)
large destructive waves resulting from vertical displacement along a fault located on the ocean floor, or a large undersea landslide triggered by an earthquake.
fault scarp
a small step on the ground surface where one side of a fault has moved vertically with respect to the other
Resonance
when material vibrate differently in response to seismic wave stimulation
Foreshock
early shaking before earthquake
aftershock
a small earthquake that follows the main earthquake
Benioff Zone
A zone of earthquake activity along the upper portion of a sinking plate, as it scrapes past the opposing plate, in a subduction zone.
calderas
a large volcanic crater, typically one formed by a major eruption leading to the collapse of the mouth of the volcano.
strata volcanoes
arge and cone shaped with a steeper slope towards the summit. consist of interleaved layers of lava, tephra, and volcanic plastic debris.
cinder cones
consist of cone shaped piles of basaltic lapilli and blocks from a single eruption
shield volcano
a broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava.
pyroclasts
Fragments of erupted rock
vesicles
small membrane sacs that specialize in moving products into, out of, and within a cell
pillow
sack shaped bodies characteristics of underwater eruption (skin freezes quickly then splits
Magnitude
Measure of the energy released during an earthquake
Intensity
how strong ground motion is at felt location
effusive eruption
An eruption that yields mostly lava, not ash; lava steadily flows out of a volcano onto the ground
explosive eruption
an eruption that is thick and sticky, has a high gas content, and is high in silica
Lapilli
pebble like bits of magma that cool in the air
-measuring an increased occurrence of gaseous emissions
-measuring an increased incidence of earthquakes
-observing changes in the shape of a volcano
-measuring an increase in heat flow
methods used by geologists to predict a volcanic eruption
extrusive igneous rock
rock that forms from the cooling and solidification of lava at Earth's surface
intrusive igneous rock
rock formed from the cooling and solidification of magma beneath Earth's surface
felsic lava
Silica-rich lava, more viscous (resists flowing), light-colored, more gases are trapped leading to more explosive eruptions.
mafic lava
high in magnesium and iron, less than 50% sillica thus less viscous which means it flows readily, and thus less gas is trapped within leading to a less explosive reaction
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