Lesson 14 Earthquakes Flashcards
This energy, which takes the form of waves, radiates in ____ directions from the earthquake’s source, called the focus.
all
why do rocks rupture creating volcanoes?
they have been subjected to stresses beyond their limit
What movements are earthquakes associated with?
movements along faults
Movements along faults are explained by __________
the plate tectonics theory
Mechanism for earthquakes was first explained by ____
H. Reid
Rocks “spring back” is a phenomena called _____
elastic rebound
What is the theory that the Earth’s outer shell is divided into several plates that glide over the mantle?
plate tectonics theory
Vibrations (earthquakes) occur as_______ returns to its original shape?
rock elastically
The movements that produce most earthquakes occur along large fractures, called ______?
faults
What is the earthquake’s source called?
focus
Aseismic fault slip that occurs in the uppermost part of the earth’s crust during the time between large stress-releasing earthquakes or as “afterslip” in the days to years following an earthquake.
Fault creep
What often follows earthquakes?
aftershocks
What often precedes earthquakes?
foreshocks
What is the study of earthquake waves?
seismology
What is a earthquake recording instrument ?
seismograph
What does a seismograph record?
movements of earth
What is the record recorded by the seismograph called?
seismogram
What are the two main groups of seismic waves generated during an earthquake?
surface waves
body waves
What does P waves stand for?
primary waves
What does S waves stand for?
secondary waves
Which wave has the slowest velocity?
Surface waves
Which wave has a complex motion?
Surface waves
Which wave “shakes” the particles in rock at right angles to their direction of travel?
S waves
Which wave push (compress) and pull (dilate) rocks in the direction the wave is traveling?
P waves
What can S waves travel through?
Solids
What can P waves travel through?
Solids
Liquids
Gases
Which wave travels along the outer layer of Earth?
Surface waves
Which wave travels through Earth’s interior?
Body waves
In solid material, how much faster does the one body wave travel than the other?
P waves travel 1.7 times faster than S waves
Name the waves from slowest to fastest velocity?
Surface waves
S waves
P waves
What is the order that the waves occur?
P waves
S waves
Surface waves
What wave is the most destructive?
Surface Waves
The place within Earth where earthquake waves originate?
focus
Point on the surface, directly above the focus?
Epicenter
How is the epicenter located?
determined using the difference in velocities of P and S waves
List three examples of Earthquake zones being closely correlated to plate boundaries?
Circum-Pacific belt (ring of fire)
Oceanic ridge system (splits Atlantic in half)
Mediterranean-Asiatic belt
How many station recordings are needed to locate an epicenter?
three
To find an epicenter, a _____ is drawn around each of the 3 stations equal to the ______distance.
The point where they _____is the epicenter.
circle
epicenter
intersect
The principal earthquake epicenter zones through the world’s oceans?
Oceanic ridge system (splits Atlantic in half)
The principal earthquake epicenter zones along the outer margin of the pacific ocean ?
Circum-Pacific belt (ring of fire)
A measure of the degree of ground shaking at a given locale based on the amount of damage?
Intensity
What is most often used to measure intensity of an earthquake?
Modified Mercalli Intensity Scale
What are the two fundamentally different measures that seismologists use to describe the size of an earthquake?
intensity and magnitude
The Modified Mercalli Intensity Scale uses damage to _______ to estimate the intensity of ground shaking for a local earthquake.
for example: in ______
buildings
california
Magnitude is calculated from seismic records and estimates the amount of energy _______ of an earthquake.
released at the source
Who introduced the concept of magnitude?
Charles Richter
What is used to express magnitude?
A tenfold increase in ground shaking corresponds to an increase of ___on the magnitude scale.
logarithmic scale
one
How is magnitude often measured?
using the Richter scale
What is the Richter scale based on?
amplitude (maximum displacement) of the largest seismic wave
Each unit of Richter magnitude equates to roughly a ____-fold energy increase?
32
Does the Richter scale estimate adequately for very large earthquakes as well?
no
What is currently used to estimate the size of moderate and large earthquakes?
Moment magnitude
What 3 things are used to calculate the moment magnitude scale ?
Average displacement of the fault
Area of the fault surface
Strength of the faulted rock
The 2 most obvious factors that determine the amount of destruction accompanying an earthquake ?
magnitude
proximity to a populated area
Name 5 secondary effects of earthquakes ?
Tsunamis Seismic sea waves Landslides Ground subsidence Fire
What are the factors that determine structural damage?
Intensity
Duration of vibrations
Nature of the material upon which the structure rests
The design of the structure
What can happen from the ground because of the quake?
Liquefaction
During liquefaction, _______material turns fluid and
underground objects may _______?
saturated
float to surface
Long-range forecasts are based on the premise that earthquakes are ______.
repetitive or cyclical
Substantial research to predict earthquakes is underway in countries where earthquake risk is ____.
high
Seismologists study the _______ of earthquakes for patterns, so their occurrences might be predicted.
history
Can seismologists predict short range or long range earthquakes?
long range
What is given when seismologists predict a quake?
a probability
What are the four major zones of Earth’s interior?
crust
mantle
outer core
inner core
Where does most of our knowledge of Earth’s interior come from?
study of P and S waves
Earth interior can be examined from the ______of P and S waves through earth depending on properties of the ______
travel times
minerals
Earth interior can be examined from the fact that s waves only go through _____
solids
What are the layers confined by?
composition
What layer of earth is a thin, rocky outer layer?
crust
Does the crust vary in thickness?
yes
How thick is the crust in oceanic regions?
about 7 km (5 miles)
How thick can the crust exceed in some mountainous regions?
70 km (40 miles)
How thick is the continental crust?
averages 35-40 km (25 miles)
What are the two parts of the crust?
Continental crust
Oceanic crust
What is the average density of continental crust?
2.7 g/cm3
What is the upper continental crust composed of ?
granitic rocks
What is the lower continental crust composed of ?
akin to basalt
How old is the continental crust?
4 billion years
How old is the oceanic crust?
180 million years younger than the continental crust
What is the composition of oceanic crust?
basaltic composition
What is the density of oceanic crust?
3.0 g/cm3
Where is the mantle located?
below the crust
What is the thickness or depth of the the mantle?
2900 km
1800 miles
What is the composition of the uppermost mantle? igneous rock peridotite
igneous rock peridotite
Does the mantle composition change with more depth?
yes
What is the radius of the outer core?
3486 km (2161 miles)
What is the average density of the outer core?
11 g/cm3
What is the outer core composed of?
iron-nickel alloy
What is the location and shape of the outer core?
below mantle
sphere
What characteristic does the outer core exhibit?
characteristics of a mobile liquid
How thick is the outer core?
2270 km
What is the radius of the inner core?
about 1216 kilometers
What is the inner core?
a solid metallic sphere
What are the three layers defined by physical properties?
Lithosphere
Asthenosphere
Mesosphere (or lower mantle)
Describe the temp., texture, and state of the lithosphere?
Cool, rigid, solid
What is the lithosphere consist of?
Crust and uppermost mantle
How thick is the lithosphere?
100 km thick
What is the depth of the asthenosphere?
660 kilometers
Where is the asthenosphere located?
beneath the lithosphere
upper mantle
Describe the texture of the asthenosphere?
soft, weak layer
easily deformed
The crust and uppermost mantle form Earth’s cool rigid outer shell called ?
lithosphere
Beneath the lithosphere lies a soft, relatively weak layer of the mantle known as the ?
asthenosphere
________ rocks such as _______ are thought to make up the mantle.
ultramafic
peridotite
What two elements is the core mainly composed of?
iron and nickel
What is the temperature of rocks in the mesosphere?
very hot
Where is the mesosphere located?
lower mantle
How many kilometers deep can the mesosphere be?
660-2900 km
What is the texture of the mesosphere?
more rigid layer
What is the flow of the rocks in the mesosphere?
capable of gradual flow
What in the outer core is responsible for the earth magnetic field?
convective flow of metallic iron
What state is the outer core?
liquid layer
How thick is the outer core?
2270 km (1410 miles)
Which layer generates earths magnetic field?
outer core
What is the radius of the inner core?
1216 km (754 miles)
What state does the inner core behave like?
solid
What shape is the inner core?
sphere
Mohorovicic discontinuity shows that the velocity of seismic waves _______ abruptly below ___ km of depth
increases
50
What does Mohorovicic discontinuity separate?
crust from underlying mantle
What says the velocity of seismic waves increases abruptly below 50 km of depth?
Mohorovicic discontinuity
How was earths major layers discovered?
using changes in seismic wave velocity (Mohorovicic discontinuity)
Absence of P waves from about 105 degrees to 140 degrees around the globe from an earthquake?
shadow zone
What explained if Earth contained a core composed of materials unlike the overlying mantle?
shadow zone
A shadow zone is the absence of ______from about ____ degrees to _____degrees around the globe from an earthquake?
p waves
105
140
What did shadow zones explain?
if Earths core had materials unlike the mantle
The size of the inner core was calculated using _____from _______generated during _______ _____tests
echos
seismic waves
underground nuclear
The inner core was discovered by noting a ______ of _____ within the ____?
new region
seismic reflection
core
What was the only thing scientists had to determine the oceanic crust composition prior to the 1960s?
seismic evidence
What made the recovery of ocean floor samples possible?
deep-sea drilling technology
It was found that mantle composition is more ________
speculative
Mantle Lava from the asthenosphere has a composition similar to that which results from the partial melting of a rock called _____
peridotite
Where does evidence of a core come from?
meteorites
What explaines earths density best?
an iron core
What concept does earths magnetic field support?
molten outer core
The core got its composition because ___, and other dense metals _____ to earth interior during the planets early history.
iron
sank
What is the range of the meteorite compositions, proving a core?
from metallic to stony
What are metallic meteorites made of?
iron and nickel
What are stony meteorites composed of?
dense rock similar to peridotite
