Earthquake Slides By Dr S A Isiorho Copyright
Earthquake Slides By Dr. S. A. Isiorho Copyright © by Isiorho 1
Earthquakes Definitions v Earthquake- the vibration of the ground due to the sudden release of energy accumulated in a deformed rock v Focus (Hypocenter)- spot underground where the rock begins to break- point at which slip initiates v Epicenter- the point on the land surface directly above the focus v Aftershock- tremors that occur as rocks adjust to their new position v Seismology- the study of earthquake Copyright © by Isiorho 2
Seismic Waves Earthquake’s energy is transmitted through the earth as seismic waves v v Two types of seismic waves radiate from the focus Body waves- transmit energy through earth’s interior v v v Primary (P) wave- rocks vibrate parallel to direction of wave (v=47 km/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 v v Love (L) wave- Rock moves from side to side like snake Raleigh ® wave- Rolling pattern like ocean wave Copyright © by Isiorho 3
Locating & Measuring Earthquake v v 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 v v Measured by the amount of damage caused in human terms- I (low) to XII (high) Richter Scale- (logarithmic scale) v v Magnitude- based on amplitude of the waves Earthquake total energy- uses moment magnitude scale Copyright © by Isiorho 4
Locating Epicenter & Focus Depth (EQ classification) v Use Arrival time at a recording station (time lag between P & S waves) to locate the epicenter of an earth quake v v Need three stations to determine the epicenter Maximum Depth of Focus Shallow focus EQ < 70 km (45 mi) most earthquakes v Intermediate focus EQ- 70 -300 km (45 - 180 mi) v Deep focus EQ- > 300 km (> 180 mi) v Copyright © by Isiorho 5
Richter Scale v 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. v 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 Copyright © by Isiorho 6
Earthquake Locations v Most EQs occur in the circum pacific region v 80% v Most of shallow focus EQ; 100% of deep focus EQ EQs occur along plate boundaries v Oceanic trenches, Benioff zones, Mediterranean. Himalayan v Most EQs in US occur near the west coast v San-Andreas Fault Copyright © by Isiorho 7
Effects of Earthquakes v Ground Displacement v Lateral and vertical Landslides v Liquefaction v v v Seiches v v Conversion of formally stable fine grain materials to a fluid mass The back & forth movement of water in a semi-closed/closed body of watercould cause flooding Tsunamisv more from submarine landslide v Fire Copyright © by Isiorho 8
Coping with Earthquake v Earthquake zone v Plate boundaries v Assessing local seismic history and future risks v Land use planning v Quake reinforcement of building/structures v Short term and Long term forecast v Contingency plan Copyright © by Isiorho 9
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