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EARTH SCIENCE LECTURE
CHAPTER 12
6.1 Earthquakes and Plate Tectonics
✧Vibrations of the earth's crust are called _________________________.
✧Earthquakes usually occur when rocks under stress suddenly shift along a
____________________.
✦________________ is a force that can change the size and shape of rocks.
✧The rocks along both sides of a fault are pressed together tightly.
✲For a time, ______________________________ prevents the rocks from moving past
each other.
✱
The fault is said to be "_______________________".
Parts of a fault remain locked until the stress becomes so great that the rocks
suddenly grind past each other.
Elastic Rebound Theory
✧Geologists explain many earthquakes by the ________________________________.
✦This theory states:
✧As they fracture and slip into new positions, rocks along a fault release energy in the
form of vibrations called ______________________________________.
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✦This release of energy often increases the stress in other rocks along the
fault, causing them to fracture and spring back.
✧Because
of this, major earthquakes are usually followed by a series of small tremors
called _______________________________.
✦The point on the earth's surface directly above the
____________________ is called the ____________________________.
✧When
an earthquake occurs, seismic waves radiate __________________ in all
directions from the focus.
✦About _______________ of continental earthquakes have a
____________________________.
1)
✦The earthquakes that usually cause
2)
3)
✦ They usually occur
✲By the time the vibrations from an intermediate-focus or deep focus
earthquake reach the surface, _____________________________.
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Major Earthquake Zones
✧
Most earthquakes occur
✧1)
✦The Pacific Ring of Fire includes the west coasts of North and South
America, the east coast of Asia, and the western Pacific islands of the
Philippines, Indonesia, New Guinea, and New Zealand.
✧
Along this ring, _______________________________________, while some plates
scrape past each other.
✦Eventually the rocks fracture and shift, and an earthquake occurs.
✧2)
✦
✧3)
✦
✦
✧At some plate boundaries there are groups of interconnected faults called
_____________________________.
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✦ Fault zones form at plate boundaries because of the intense stress that
results when the plates _______________________________________.
✧EXAMPLE:
✦ The
✲The San Andreas Fault zone has formed where the edge of the Pacific
plate slips northwest along the North American plate.
✧
Not all quakes result from movement along plate boundaries.
✧EXAMPLE:
✦
✲
✱This discovery occurred in the _________________________
6.2 Recording Earthquakes
✧Seismic waves can be detected and recorded by using an instrument called a
______________________________.
✧A seismograph consists of
_______________________________________:
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✦1)
✦2)
✧A seismograph records motion by tracing wave-shaped lines on paper or by
translating the motion into electronic signals.
✧The electronic signals can be recorded on magnetic tape or directly loaded into a
computer that analyzes the seismic waves.
✧Every earthquake produces three major types of seismic waves:
✦ 1)
✲P waves cause rock particles to move together and apart along the
direction of the waves.
✧2)
✦S waves cannot be detected on the opposite side of the earth from the
earthquake's epicenter.
✦S waves cause rock particles to move at right angles to the direction in
which the waves are traveling.
✧3)
✦
✦
✦
✦L waves, which cause the surface to rise and fall, are particularly destructive
when traveling through loose earth.
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✧____________________________ is used to express the magnitude of an earthquake.
✦Magnitude is a
✦Each increase of one whole number of magnitude represents the release of
_________________ more energy than that of an earthquake measuring one
whole number lower.
✧An earthquake with a magnitude of 8 releases 31.7 x 31.7 - or about 1,000 times -as
much energy as an earthquake with a magnitude of 6.
✦The largest earthquake so far recorded registered a magnitude of
_________.
✧A _______________________, one that causes widespread damage, has a
magnitude ___________________________.
✧A ______________________________ has a magnitude between ___________
✧A ___________________________, between _________________________.
✧
Earthquakes with magnitudes of _____________________ are called
________________________ and usually are not felt by people.
✧The ________________________ expresses the intensity of an earthquake, or the
amount of damage it causes, by Roman numerals from _______________and
______________________________.
✦A rating of II, which has a low intensity, as follows:
✲
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✧
A numeral X, is described as follows:
✦
✧
The highest intensity earthquake, Roman numeral XII and is described as:
✦
6.3 Earthquake Damage
EARTHQUAKE SAFETY RULES
✦1)
✦2)
✦3)
✧A major earthquake with an epicenter on the ocean floor sometimes causes a giant
ocean wave called a ___________________________.
✦This name comes from the Japanese word for "____________________".
✧Scientists think that most tsunamis are caused by two events related to undersea
earthquakes:
✦ 1)
✲
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✧2)
✦
✲Disastrous earthquakes and tsunamis have encouraged the expansion and
improvement of the _____________________________________
____________________________________________________.
✧This network of seismograph stations around and in the ____________________
alerts scientists to the location and magnitude of earthquakes.
✦If a tsunami seems possible, scientists estimate its arrival times at different
locations. They can then issue warnings immediately to these areas.
✦There will not be enough time to issue tsunami warnings to areas very near the
epicenter of the earthquake.
✧One of the earliest means of predicting earthquakes was
✲Some animals appeared nervous and restless, almost as if they could sense the coming
catastrophe.
✲___________________ research into strange animal behavior as an effective
earthquake warning continues.
✧Some areas experience major earthquakes ________________________________.
✦ To make more accurate predictions, scientists are trying to detect changes in the
earth's crust that can signal an approaching earthquake.
✲
✲
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✦Along some faults, scientists have identified zones of immobile rock called
___________________________________.
✲ A seismic gap is a
✲ The strain in the surrounding rock has increased, and no major earthquake has
occurred in this location for at ______________________________.
✧Scientists think seismic gaps are likely locations of _________________________.
✦Several gaps that exist along the ___________________________ will
probably be sites of major earthquakes in the future.
✧Sometimes scientists detect a _____________________________________shortly
before an earthquake.
✦ They are also able to detect the strain and cracks in rocks caused by the stress that
builds up just before an earthquake.
✲The magnetic and electrical properties of rock change when these cracks fill
with water. As a result, scientists might be able to detect small changes in
the earth's magnetic field and in the way electricity is conducted by rocks
prior to an earthquake.
✧Scientists can also
✧Some earthquakes are preceded by a
✦ The P waves being measured have traveled from distant earthquakes.
✲
✲
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✲
✧
Scientists would like to be able to control the force of earthquakes.
✦
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