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Earthquake Slides

By Dr. S. A. Isiorho

Copyright © by Isiorho 2

EarthquakesDefinitions Earthquake- the vibration of the ground due to the sudden

release of energy accumulated in a deformed rock Focus (Hypocenter)- spot underground where the rock

begins to break- point at which slip initiates Epicenter- the point on the land surface directly above the

focus Aftershock- tremors that occur as rocks adjust to their new

position Seismology- the study of earthquake

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Seismic WavesEarthquake’s energy is transmitted through the earth as seismic waves Two types of seismic waves radiate from the focus Body waves- transmit energy through earth’s interior

Primary (P) wave- rocks vibrate parallel to direction of wave (v=4-7km/sec) Compression and expansion (slinky example)

Secondary (S) wave- rocks move perpendicular to wave direction (v=2-5 km/sec)

Rock shearing (rope-like or ‘wave’ in a stadium) S-wave cannot travel through liquid

Surface waves- transmit energy along earth’s surface Love (L) wave- Rock moves from side to side like snake Raleigh ® wave- Rolling pattern like ocean wave

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Locating & Measuring Earthquake Seismometer- instruments that detect seismic waves Seismograph- device that measures the magnitude of

earthquake seismogram is visual record of arrival time and magnitude of

shaking associated with seismic wave Mercalli Intensity scale

Measured by the amount of damage caused in human terms- I (low) to XII (high)

Richter Scale- (logarithmic scale) Magnitude- based on amplitude of the waves Earthquake total energy- uses moment magnitude scale

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Locating Epicenter & Focus Depth (EQ classification)

Use Arrival time at a recording station (time lag between P & S waves) to locate the epicenter of an earth quake Need three stations to determine the epicenter

Maximum Depth of Focus Shallow focus EQ < 70 km (45 mi) most earthquakes Intermediate focus EQ- 70-300 km (45- 180 mi) Deep focus EQ- > 300 km (> 180 mi)

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Richter Scale Richter scale is based on a log scale, meaning that each

subsequent number is ten times more in amplitude of vibration- this translates to about 30 times more energy than the previous number.

Example: an EQ of 5.0 is 10 times greater than an EQ of 4.0 on the Richter scale and is 30 times more in energy. An EQ of 5.0 is 100 times greater in amplitude than an EQ with 3.0 reading on the Richter scale

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Earthquake Locations

Most EQs occur in the circum pacific region80% of shallow focus EQ; 100% of deep focus EQ

Most EQs occur along plate boundariesOceanic trenches, Benioff zones, Mediterranean-

Himalayan Most EQs in US occur near the west coast

San-Andreas Fault

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Effects of Earthquakes Ground Displacement

Lateral and vertical

Landslides Liquefaction

Conversion of formally stable fine grain materials to a fluid mass

Seiches The back & forth movement of water in a semi-closed/closed body of water- could

cause flooding

Tsunamis- more from submarine landslide

Fire

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Coping with Earthquake

Earthquake zone Plate boundaries Assessing local seismic history and future risks Land use planning Quake reinforcement of building/structures Short term and Long term forecast Contingency plan