Transcript - Toolbox Pro

Earthquakes and
Plate Tectonics
Our Violent Earth
The Earth’s Changing Crust
► Todays
evidence: EQ’s, volcanic eruptions,
mountain growth, moving landmasses.
► Past movements based on the concept of
ORIGINAL HORIZONTALITY: Assumes that
sed. Rocks and some extrusive igneous.
Rock form in horizontal layers parallel to the
earths surface.
Past evidence of crustal movement
► Deformed
rock layers such as folded rock,
faulted rock, tilted rock, uplifted rock (with
displaced fossils.)
See page 214 of book.
Crustal Change in depth
► Folds:
bends in crust caused by compressional
stresses
 Anticlines: up-turned folds: Hills
 Synclines: down-turned folds: valley
 Tilts are just eroded sections of the above.
► Faults:
Breaks in the crust where movement occurs
 Normal: hanging wall moves down
 Reverse: hanging wall moves upward
 Strike-slip: one block slides past the other laterally
► Mountains
elevation
(uplift): up-thrust crust material at high
Earthquakes
► The
natural, rapid shaking of the
lithosphere caused by release of energy
stored in rocks
► Most earthquakes are caused by:
FAULTING
 The grinding of pieces of crust past one
another
► Some
are causes by the movement of
magma within the lithosphere under
volcanoes
Earthquake Terminology
► Seismic
Waves:
 The shock waves of a quake
► P-Waves:
 Primary waves; fastest wave, first to be recorded;
particles vibrate in the direction of movement, like a
sound wave; travel through solids and liquids
► S-Waves:
 Secondary waves; second to be recorded; particles
vibrate at right angles to the direction of movement,
like a water wave; travel through solids only
► Focus:
 Point below earth’s surface where the energy is
released
► Epicenter:
 Point on earth’s surface above the focus; most
damage is done here
Why Study Earthquakes
► Develop
an “early warning” or “prediction
system”
► Seismic waves give scientists information on
the inner layers and composition of the
Earth
 Different materials allow seismic waves to act
differently
VELOCITY OF SEISMIC WAVES
► Velocity
depends on the material they are
passing through
a. Increase density and pressure – greater the
velocity
b. Waves are refracted or bent as waves pass
through material with different densities
EARTHQUAKE SHADOW ZONES
► At
an angle of 103° (distance 11,000 kms)
from the epicenter both P and S waves
disappear
►P
waves can again be detected at l42°
(16,000 kms.)
NO S WAVES EVER APPEAR AGAIN
► THIS
BAND OF 39° IN WHICH NO WAVE
ARE OBSERVED IS CALLED THE
EARTHQUAKE’S SHADOW ZONE
EARTHQUAKE
SHADOW
ZONES
P WAVES
DISAPPEAR
FROM
105º -140º
S WAVES
DISAPPEAR
FROM 105º
NEVER TO
APPEAR
AGAIN
ANALYSIS OF
SEISMIC WAVES
HAVE RESULTED
IN THE
INFERENCE
ABOUT EARTH’S
INTERIOR
S WAVES CANNOT
PASS THROUGH
THE LIQUID
OUTER CORE
Earthquake Magnitude
► The
strength of an earthquake
► Measured on an intensity scale
► Ex: Richter Scale
Seismograph needle and
readout; shows P and S
Waves being recorded
Earthquake Magnitude Scale
Japanese
Magnitude Scale
from 0 - 7
Seismograph
Traditional Mechanical
Seismograph
March 28, 2005, near Northern Sumatra,
Indonesia. This 8.7 magnitude
earthquake came only three months after
the devastating magnitude 9.0
earthquake of December 26, 2004, which
caused the Tsunami.
Locating the Epicenter of an
Earthquake (Steps)
1.
2.
3.
4.
5.
Acquire P and S wave data from at least 3
monitoring stations.
Calculate the difference in arrival times
between the P and S waves for each station.
Use your reference tables to determine the
distance that station is from the epicenter.
Strike a circle with the scaled diameter of the
distance you just calculated.
Do this 2 more times; where all 3 meet is the
location of the epicenter.
LOCATING EARTHQUAKE EPICENTER
MUST HAVE DISTANCE FROM
3 SEISMOGRAPH STATIONS TO
DETERMINE EPICENTER
Practice Using the P and S wave
Arrival Time Chart
1.
If the P wave arrived at 02:00:00 and the S
wave arrived at 02:04:00, find the distance the
station is from the epicenter.
2.
If the P wave arrived at 12:12:00 and the S
wave arrived at 12:24:30, find the distance the
station is from the epicenter.
3.
If the P wave arrived at 09:15:30 and the S
wave arrived at 09:18:50, find the distance to
the station.
Practice Using the P and S wave
Arrival Time Chart
4.
If a monitoring station were 8200 km from
the epicenter of an earthquake. If the Pwave arrived at 2:15 PM, find the time the
earthquake occurred.
5.
If a seismic station was 2600 km from the
epicenter of a quake and it recorded an Swave at 1:00 PM, find the time the quake
occurred.
Practice Using the P and S wave
Arrival Time Chart
6.
If an earthquake occurred at exactly 7hr:
45 min: 00 sec. and the p-wave arrived at
a station at 7 hr: 52 min: 00 sec, when did
the s-wave arrive?
7.
An earthquake exactly 8000 km away from
a station occurred at 3 hr: 03 min: 00 sec.
When did the P-waves arrive? When did
the S-waves arrive?
NORMAL FAULT
REVERSE FAULT
TRANSFORM FAULT
Plate Tectonics
► The
theory that suggests Earth’s lithosphere is
broken up into sections (lithospheric plates or
tectonic plates) and their movement and
interactions produce major changes in Earth’s
surface
► At the plate boundaries you’ll find: Earthquakes,
volcanoes, trenches, mountains and mid-ocean
ridges-Zones of frequent crustal activity!!! Ex:
Pacific Ring of Fire
Sea-Floor Spreading
► Brand
new ocean crust (basalt) is being
made and is spreading out from the ridge.
► Evidence:
► Alternating zones of reversed magnetic
polarity at equal distances from the ridge.
► The age of the basaltic rock gets older at
equal distances from the ridge.
Continental Drift
► The
movement of continents with respect to
one another.
► Evidence:
► “Jig Saw Puzzle Effect”
► Similarities of rocks, minerals, fossils and
age at continental margins.
► Some mountain chains line up when the
continents are put back together.
Driving Force Behind Plate Tectonics
► Convection
Currents in the mantle of Earth
► Convection currents work like tank tracks
and cause the plates to move by slowly
dragging them around Earth’s surface
Earth’s Surface over time
► Reference
tables: page 9; right column
► The Location of the North America has
changed throughout geologic history
► The continents have been connected 2
times throughout geologic time and have
subsequently broken up due to plate
movements
► If this process continues, we will be part of
a new super-continent in another 250
million years
Plate Boundaries
► Divergent
Plate Boundaries: Crustal
plates move apart (Ex. Mid-ocean Ridge)
Plate Boundaries
► Convergent
Boundaries: crustal plates
move toward each other; cause collisions
► Ex. Ocean Trench
Plate Boundaries
► Transform
Boundaries: one
plate slips past
another with no
vertical motion;
San Andreas
Fault, California
NORTH
SAN ANDREAS FAULT
PACIFIC PLATE
WEST SIDE
MOVES NORTH
EAST
WEST
NORTH
AMERICAN
PLATE
EAST SIDE
MOVES SOUTH
SOUTH
Test Review
►Test
is coming!!!
►Castle Learning Review
►Earthquakes and Plate
Tectonics Review
►Will help out with the
upcoming test