EarthquakesBasic Introduction

Seismometer

Seismogram

P waves

Earth: Portrait of a Planet, 4th EditionCopyright © 2012 W. W. Norton & Company

S Waves

Earth: Portrait of a Planet, 4th EditionCopyright © 2012 W. W. Norton & Company

LOCATING THE EPICENTER OF AN EARTHQUAKE

Three seismograms are needed (Triangulation)

Costa Rica, Ireland and Philippines

Seismogram for Costa RicaP wave

S wave

Surface wave

10:15AM 10:20AM 10:25AM 10:30AM

Seismogram for Costa Rica

Richter Scale

Amount of energy released during an earthquake

MERCALLI INTENSITY SCALE

Intensity

Description Destructiveness (Extent of damage)

I Instrumental Detected only by instruments; causes no damage

II Feeble Felt by a few stationary people, especially in the upper floors of buildings; suspended objects like lamps may swing.

III Slight Felt indoors; standing automobiles sway on their suspensions; it seems as though a heavy truck is passing.

IV Moderate Shaking awakens some sleepers; dishes and windows rattle.

V Rather strong Most people awaken; some dishes and windows break, unstable objects tip over; trees and poles sway.

VI Strong Shaking frightens some people; plaster walls crack, heavy furniture moves slightly, and a few chimneys crack but overall little damage occurs.

VII Very Strong General alarm; Most people are frightened and run outside; a lot of plaster cracks, windows break, some chimneys topple, and unstable furniture overturns; poorly constructed buildings sustain considerable damage.

VIII Destructive Many chimneys and factory smokestacks topple; masonry cracks; heavy furniture overturns; substantial buildings sustain some damage, and poorly constructed buildings sustain severe damage.

IX Ruinous Some buildings collapse; frame buildings separate from their foundations; most buildings sustain damage, and the ground cracks, underground pipes break and rails bend: some landslides occur.

X Disastrous The ground severely cracks in places; most masonry structures and some well constructed wooden structures are destroyed; many landslides occur along steep slopes; some bridges collapse; some sediment liquefies; concrete dams may crack; facades on many buildings collapse; railways and roads suffer severe damage.

XI Very Disastrous Few masonry buildings remain standing; many bridges collapse; broad fissures form in the ground; most pipelines break; severe liquefaction of sediment occurs; some dams collapse; facades on most buildings collapse or are severely damaged.

XII Catastrophic Earthquake waves cause visible undulations of the ground surface; objects are thrown up off the ground; there is complete destruction of buildings and bridges of all types.