Transcript Earthquakes Seismic Waves Day 1

AIM: Describe the origin of an earthquake, types of seismic
waves and how earthquakes are measured and their
epicenter located?
OBJ: Given notes and activity sheet SWBAT describe the
origin of an earthquake, types of seismic waves and how
earthquakes are measured and their epicenter located with
70% accuracy.
DN: HW Check- Forces in Earth’s Crust Act. Sheet
ACT: Introduction to earthquake anatomy, types of seismic
waves, measuring and locating the epicenter of an
earthquake.
Watch Nova Video (14 min): https://www.youtube.com/watch?v=SPbLpE5tQ_A
HW: Work on Tectonics Activity Sheet; Tectonics Exam,
Friday, Feb. 13.
EARTHQUAKE ANATOMY
Earthquake: shaking of Earth’s surface due to
movement of rock along a fault. This movement
comes from the release of stress occurring
within rocks of the tectonic plates.
Focus: the location beneath Earth’s surface
(~ 100 km depth) where rock that is under stress
breaks; earthquake (P- & S-wave) origin.
Epicenter: location on the Earth’s surface
directly above the focus
Types of Seismic Waves
Earthquakes produce seismic (energy carrying) waves that race
outwards from the focus in all directions. These waves move
through the earth’s interior and across the surface.
Types of Seismic Waves:
P-waves: “Primary”, fastest, S,L; waves
compress and expand the ground like an
accordian/slinky.
S-waves: “Secondary”, slower, S; waves move
side to side and up and down shaking ground
back and forth; violent building/bridge damage;
Absent from Earth’s outer core.
Rayleigh Waves: when P- & S- waves reach
the surface, these surface (rolling) waves cause
severe damage
Measuring Earthquake Strength:
Seismograph: instrument used to measure and
record seismic wave magnitude.
Magnitude: amount of energy released.
Mercalli Scale: descriptive scale (containing 12
steps) to measure level of damage from an
earthquake.
Richter Scale: measures magnitude (strength)
of earthquake by the size of the seismic waves.
Each one-point increase equals 32 times more
energy released (logarithmic scale)
Seismograph
Richter (logarithmetic) Scale
relative strength
Magnitude
1,000,000,000,000,000x
10,000,000,000,000x
1,000,000,000,000x
10,000,000,000x
1,000,000,000x
33,554,432x
1,048,576x
LEGEND
Catastrophic
Severe
Moderate
Mild
0
1
2
3
4
5
6
7
8
9
10
32,768x
Richter Value
1024x
32x
Locating The Epicenter:
To determine the location of an epicenter,
scientists determine the difference between the
arrival times of the P-wave and S- wave.
The farther away an earthquake is, the greater
the time between the arrival of the P-wave and
the S-wave.
By drawing at least three circles using data from
different seismographic stations, the intersection
of the circles is the location of the epicenter.