EARTHQUAKE NOTES

EARTHQUAKE NOTES

SHAKING UP THE EARTH

EARTHQUAKES

•What is anearthquake?

•A tremendous releaseof pressure from theearth that causesshockwaves to shakethe earth.

EARTHQUAKES

•What causesearthquakes?

•The shifting of theground due to platetectonics or fault lines

EARTHQUAKE DEFINITIONS

•FAULT LINE

•EPICENTER

•FOCUS

•The line on which theearth’s crust moves

•The point on theearth’s surface wherethe earthquakeoccurred.

•The exact point in theearth’s surface wherethe earthquakeoccurred.

Epicenter and Focus

MORE DEFINITIONS

•SEISMIC ACTIVITY

•SEISMOLOGIST

•SEISMOMETER

•SEISMOGRAPH

•Earthquake activity

•A person who studiesearthquakes

•A machine designedto pick up andinterpret seismicwaves

•The graph created bythe seismometer

MORE DEFINITIONS

•SEISMIC WAVES

•The shockwavescreated by theearthquake. Thereare two types

•Body waves travelthrough the earth

–Primary waves

–Secondary waves

MORE DEFINITIONS

•SEISMIC WAVES

•Surface waves travelonly on the surface

–Love waves

–Rayleigh waves

BODY WAVES

•Primary waves

•Travel the fastest likea sound wave

•Go through the entireearth

BODY WAVES

•Secondary waves

•S-waves travelthrough the earth arethe second fastest

•Travel perpendicularto the ground

•Will not travel throughthe liquid outer core

SURFACE WAVES

•Rayleigh waves andlove waves

•Only travel on thesurface but do themost damage.

•Rayleigh waves rollthe ground like anocean wave.

•Love waves move theground side to side

MEASURING AN EARTHQUAKE

•How do we measurean earthquake?

•We use to use theModified Mercalliscale. It could onlymeasure the intensity.(the damage of theearthquake.)

•Now we use theRichter Scale, itmeasures themagnitude. (power)

Modified Mercalli scale

•How was it used?

•People would givetheir own accounts ofthe quake.

•Problems: Oneearthquake couldhave many differentintensity numbersbecause of thevarious locations ofthe 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 anearthquake. 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 makecracking 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 maystop.

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; considerabledamage 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 insubstantial 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 therichter scale

•It measures themagnitude of theearthquake by lookingat the seismic waves

•It is based on powersof ten

•A 3 on the RichterScale is 10 timesmore powerful than a2

M=1 to 3: Recorded on local seismographs, but generally not feltM=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 (1906San Francisco, 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).