EARTHQUAKE NOTES SHAKING UP THE EARTH

EARTHQUAKES What is an earthquake? A tremendous release of pressure from the earth that causes shockwaves to shake the earth.

EARTHQUAKES What causes earthquakes? The shifting of the ground due to plate tectonics or fault lines

EARTHQUAKE DEFINITIONS FAULT LINE EPICENTER FOCUS The line on which the earth’s crust moves The point on the earth’s surface where the earthquake occurred. The exact point in the earth’s surface where the earthquake occurred.

Epicenter and Focus

MORE DEFINITIONS SEISMIC ACTIVITY SEISMOLOGIST SEISMOMETER SEISMOGRAPH Earthquake activity A person who studies earthquakes A machine designed to pick up and interpret seismic waves The graph created by the seismometer

MORE DEFINITIONS SEISMIC WAVESThe shockwaves created by the earthquake. There are two types Body waves travel through the earth –Primary waves –Secondary waves

MORE DEFINITIONS SEISMIC WAVESSurface waves travel only on the surface –Love waves –Rayleigh waves

BODY WAVES Primary wavesTravel the fastest like a sound wave Go through the entire earth

BODY WAVES Secondary wavesS-waves travel through the earth are the second fastest Travel perpendicular to the ground Will not travel through the liquid outer core

SURFACE WAVES Rayleigh waves and love waves Only travel on the surface but do the most damage. Rayleigh waves roll the ground like an ocean wave. Love waves move the ground side to side

MEASURING AN EARTHQUAKE How do we measure an earthquake? We use to use the Modified Mercalli scale. It could only measure the intensity. (the damage of the earthquake.) Now we use the Richter Scale, it measures the magnitude. (power)

Modified Mercalli scale How was it used?People would give their own accounts of the quake. Problems: One earthquake could have many different intensity numbers because of the various locations of the earthquake

I. Not felt except by a very few under especially favorable conditions. II. Felt only by a few persons at rest, especially on upper floors of buildings. III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated. IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed, walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop. VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight. VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent. XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly. XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.

Richter Scale How do we use the richter scale It measures the magnitude of the earthquake by looking at the seismic waves It is based on powers of ten A 3 on the Richter Scale is 10 times more powerful than a 2

M=1 to 3: Recorded on local seismographs, but generally not felt M=3 to 4: Often felt, no damage M=5: Felt widely, slight damage near epicentre M=6: Damage to poorly constructed buildings and other structures within 10's km M=7: "Major" earthquake, causes serious damage up to ~100 km (recent Taiwan, Turkey, Kobe, Japan, and California earthquakes). M=8: "Great" earthquake, great destruction, loss of life over several 100 km (1906 San Francisco, 1949 Queen Charlotte Islands).1949 Queen Charlotte Islands) M=9: Rare great earthquake, major damage over a large region over 1000 km (Chile 1960, Alaska 1964, and west coast of British Columbia, Washington, Oregon, 1700).west coast of British Columbia, Washington, Oregon, 1700)

FINDING THE EPICENTER OF AN EARTHQUAKE How do scientists find the epicenter of an earthquake? They use triangulation Using the difference in arrival times between the P and S waves, they can calculate how far the epicenter is. From 3 points they can triangulate the epicenter

TSUNAMI What is a tsunamiA giant tidal wave caused by an earthquake under the ocean Ships in the ocean may not feel it, but as it gets toward shallow waters it grows