# Earth Science, Chapter 19 , Earthquake Study Guide

seismogram
the paper recording of the earthquake

Earthquake
Release of seismic (very big) waves due to shaking of the earth. This occurs along the fault line where two pieces of the earth’s crust are usually sliding past one another

seismograph or seismometer
instruments that measure the earthquake energy, the strength of an earthquake.

stress
the build up of stress on rocks on the earth

strain
a. Deforming of crust as a result of a buildup of stress.
b. The deforming of rock layers due to stress on rocks or rock layers.

fault
a.The crack, gap or fracture or break in the earth’s crust .
b. Energy builds up along a fault for years and years and then the energy is released as an earthquake.

footwall
part of the fault wall you can walk up. the block BELOW the hanging wall.

hanging wall
part of the wall you cant walk up, when rocks slip past each other in faulting, the UPPER or overlying block along the fault plane.

Using 3 seismograph locations
you can pinpoint ONE LOCATION WHERE the earthquake takes pace.

using 2 seismograph locations
lets you know WHERE THE TWO LOCATIONS where an earthquake would occur

using 1 seismograph location
shows you HOW FAR an earthquake was from a location

faults
a. if the Earths crust BREAKS and SHIFTS from stress it will do it here.
b. a fracture along which there is SLIDING motion from forces.

focus
point directly WITHIN Earth where earthquake originates

epicenter
point on Earth’s surface DIRECTLY ABOVE the Focus

three types of stress
compression, tension and shear

compression stress
a.pushing together/ shortening
b. fault associated with: REVERSE

tension stress
a.pulling apart/ lengthening
b. fault associated with: NORMAL

shear stress
a.twisting
b fault associated with: STRIKE SLIP

three types of faults
Normal, reverse, and strike-slip

normal fault
a. caused by: TENSIONAL stress
b. causes VERTICAL movement & EXTENSION
c. NO–rock layers not continuous

reverse fault
a. caused by: COMPRESSIONAL stress
b. causes VERTICLE movement and SHORTENING
c. NO –rock layers not continuous

strike-slip fault
a. caused by: SHEAR stress
b. HORIZONTAL movement
c. YES –rock layers stay continuous

Types of Seismic waves
Primary (P-wave), Secondary (S-wave) , Surface (L-wave)

Primary (P-wave) seismic wave
a. FASTER speed
b. travels through SOLID, LIQUID and GAS.
c. starts at FOCUS -INSIDE
d. COMPRESS and EXPEND the earth
d. least damage

Secondary (S-wave) seismic wave
a. SLOWER than P-wave; SECOND FASTEST
b. travels through ONLY solids (stops at liquid)
c. start at the FOCUS-INSIDE
d. moves SIDE TO SIDE
e. second most damage

Surface (L-wave) seismic wave
a. SLOWEST of the waves
b. start at the EPICENTER
c. rolling motion on the surface
d. caused MOST damage

Magnitude
measures the ENERGY released at the SOURCE of the earthquake. determined from measurements on Seismographs.

Richter Scale
a. measures amount of ENERGY RELEASED by the EARTHQUAKE AND WAVE MAGNITUDE.
b. Measures from 1-10 or higher by using a SEISMOGRAPH(i.e. a 4.0 is like a small atomic bomb)
c. used in most countries

Mercalli scale
a. measures INTENSITY/DAMAGE of earthquake
b. measures from 1-12 in roman numerals (I, II, III, IV,V…etc)
c. used in European countries

Intensity
a.determined from effects on people, structures and the natural environment .
b.measures the STRENGTH OF SHAKING produced by earthquake.