Geology 101 Quiz 14 Flashcards
earthquakes occur when
stresses build up inside the earth to point where they exceed the strength of the surrounding rock, or exceed the force of friction holding two sides of a fault in place
red colored dots (the deepest earthquakes) on an earthquake map are associated with
subduction zones
red dots on the left side of a plate boundary mean which plate is being subducted?
the right side plate
the subducting plate will always be on the same side as
the trench
seismic waves
aka ground waves; generated when rock is flexed and snaps back into place after the rock breaks or slides along a fault
elastic rebound
flexed rock snaps back into place after a rupture
slip
the amount of displacement
P waves (primary waves)
compressional waves; do not form the traditional “S” shape of an ocean wave, but compress and expand rock as they travel - like a slinky
which type of seismic waves are the fastet?
P waves (primary waves)
P waves travel through the earth’s
liquid outer core
S waves (secondary waves)
have the characteristic “S” shape of an ocean wave
S waves are (slower/faster) than P waves
slower
S waves travel through
solids, but not liquids
P waves travel through
solids and liquids
surface waves
also have the characteristic “S” shape, but travel only along the surface
slowest waves that cause the most damage
surface waves
seismic waves are measured using a
seismometer/seismograph
P waves are (back and forth/up and down)
back and forth
S waves are (back and forth/up and down)
up and down
focus
location where the slip occurred beneath the surface
epicenter
point on the surface directly above the focus
which scale is preferred by many geophysicists?
Moment Magnitude Scale
the Richter Scale provides a measurement of the energy of an earthquake where?
at the epicenter
each number on the Richter Scale is ? times more powerful than the previous number
10 (logarithmic scale)
on the Richter Scale, we can feel an earthquake starting at about magnitude ? and earthquakes are destructive starting at about magnitude ?
3; 5
the Modified Mercali Scale is a measure of
the destructiveness of an earthquake where felt
the Richter scale has no theoretical limits and reported intensities can include decimal values, but the Mercali scale is divided into ? discrete categories
12
roman numerals up through twelve
one I two II three III four IV five V six VI seven VII eight VIII nine IX ten X elevel XI twelve XII
on the modified Mercalli scale, intensity level I description
not felt except by a very few under especially favorable conditions
modified Mercalli scale intensity level VI description
slight damage; felt by all
modified Mercalli scale intensity level XII description
damage total; lines of sight and level are distorted; objects thrown into the air
seismic waves attenuate (?) more as they travel through ? than through ?
grow weaker; rock than through unconsolidated sediments
do earthquakes kill people directly? if not, what does?
no; collapsing buildings, fire, landslides, tsunamis
are tallest buildings at greatest risk?
no
how can a fire start during an earthquake?
ruptured gas lines
what are the two ways earthquakes can generate tsunamis?
- If a submarine normal, reverse, or thrust fault slips, water will be displaced and generate a wave (the slippage causes the tsunami, not the seismic waves).
- An earthquake can shake loose sediment causing a submarine landslide. The ocean surface suddenly drops above the source of the slide, and is suddenly elevated above where the slide travels, both creating a large wave.
waves from a tsunami (weaken/strengthen) as they radiate
weaken
early warning tremors help predict earthquakes because
small earthquakes often precede big earthquakes
how does the seismic gap method help predict earthquakes?
big earthquakes sometimes occur at approximately regular intervals
how does monitoring movement and stress along faults help predict earthquakes?
when a segment of a fault slips, stress increases on adjacent locked segments; if segments slip in sequence, the next slip point may be predicted
one unique use of seismic waves is the detection of ?
underground nuclear weapons testing
nuclear blasts yield a high-energy initial ? that dies out rapidly, with very little ?
P-wave; S-waves
seismic waves help to monitor volcanoes: setting off blasts or striking the ground on one side of the volcano and then measuring the seismic waves on the other side helps because
P waves will pass through liquid magma and S waves will not; by analyzing the “shadow” created by missing S waves, the size of the magma chamber and any changes over time can be monitored
seismic waves help us to explore the earth’s
interior
