EARTHQUAKES

A. Definition- a sudden vibration or trembling in the Earth’s crust.

B. Causes 1. Earthquake motion is caused by the quick release of stored potential energy into the kinetic energy of motion. 2. Most earthquakes are produced along faults, tectonic plate boundary zones, or along the mid-oceanic ridges.

C. Features of an Earthquake 1. Focus - a point in the earth’s crust where the earthquake originates.

2. Epicenter -point on the earth’s surface directly above the focus.

D. Earthquake Waves Primary Waves or P-Waves (Compressional Waves) Travel through solids, liquids and gases. b. They cause rock particles to vibrate in the same direction as the wave is traveling. c. They are the fastest traveling EQ waves.

P-Waves

2. Secondary Waves or S-Waves Shear Waves a. Travel through solids, only. b. They cause rock particles to vibrate at right angles to the direction of travel of the wave. c. They travel slower than P-waves.

S-Waves

II. Locating Earthquakes A. Seismographs -detect and record the magnitude of an earthquake.

B. Seismograms -a recording of P, S and L waves and their time of arrival.

Triangulation

Epicenter and Focus Seismic waves do not travel in straight lines. The waves are bent as they move from a medium of one density into a medium of a different density

E. Shadow Zone- An angular distance from an earthquake where P-waves are bent or refracted and S-waves are stopped by the liquid outer core.

F. Velocity and Density-the denser the material, the faster the waves move.

C. Earthquake Intensity Richter Scale-measures the magnitude of Earthquakes. Richter scale no. No. of Typical effects of this magnitude EQ’s /yr. < 3.4 800 000 Detected only by seismometers 3.5 - 4.2 30 000 Just about noticeable indoors 4.3 - 4.8 4 800 Most people notice them, windows rattle. 4.9 - 5.4 1400 Everyone notices them, dishes may break, open doors swing. 5.5 - 6.1 500 Slight damage to buildings, plaster cracks, bricks fall. 6.2 6.9 100 Much damage to buildings: chimneys fall, houses move on foundations. 7.0 - 7.3 15 Serious damage: bridges twist, walls fracture, buildings may collapse. 7.4 - 7.9 4 Great damage, most buildings collapse. > 8.0 One every Total damage, surface waves seen, objects thrown 5 to 10 years in the air.

2. Modified Mercalli Intensity Scale

III. Emergency Preparedness- A. Before an Earthquake Strikes 1. Develop an evacuation plan. 2. Know the safe spots in each room: under sturdy tables, desks, or against inside walls. 3. Conduct practice drills. 4. Learn how to shut off gas, water and electricity in case the lines are damaged.

B. During and Earthquake DROP, COVER, HOLD 1. Duck or drop down to the floor. 2. Take cover under a sturdy desk, table or other furniture. 3. If outdoors, stay away from trees and power lines.

4. If you take cover under a sturdy piece of furniture, hold on to it and be prepared to move with it. HOLD the position until the ground stops shaking and it is safe to move.

C. After an Earthquake Strikes 1. Check for injuries, render first aid. 2. Check utilities; because of possible gas leak, do not light matches. 3. Use radio and listen for emergency reports.

D. Tsunami Preparedness Tsunami-means ‘harbor wave’, a huge wave created by an EQ in the ocean crust.

1. Move inland to higher ground. 2. Stay away from the beach. 3. Generally there is a noticeable recession of the water away from the shoreline, move away quickly.