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.

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 ANATOMYEarthquake: 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 WavesEarthquakes 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

0 1 2 3 4 5 6 7 8 9 10

32x

1024x

32,768x

1,048,576x33,554,432x

1,000,000,000x10,000,000,000x

1,000,000,000,000x

10,000,000,000,000x

1,000,000,000,000,000x

Richter (logarithmetic) Scale

Mag

nit

ud

e

relative strength

Richter ValueMildModerate

Severe

Catastrophic

LEGEND

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.