Chapter 4

faults: planar breaks in rock along which there is displacement of one side relative to the other.

creep: aseismic slip. movement along faults that occurs gradually and smoothly

earth quake, sicemic slip: when stress exceeds the rupture strength of rock along the edge of a fault, a suddenmovement occurs to relaese the stress.

elastic rebound: when rocks relaesed from stress during an earth quake snap back to elastically to thier original position this is known as elastic rebound.

focus or hypocenter: the underground point at which the first movement along a fault occurs.

epicenter: (hypocenter) the point on earth's surface directly above the focus.

siesmic waves stored up energy released during an eatch quake that travel away from the focus

P waves: compressional waves, travel faster

S waves: shear waves, involves a side to side or up and down motion of molecules, slower wave. but still very fast.

siesmic surface waves: are similar to sufrace waves on water, they cause the ground to be displaced in such a way that the earth is displaced in ripples.

seismograph: a device used to detect and measure ground motions

primary waves: first waves to reach an area, the P waves, compressional

secondary waves: the waves comeing after the initial waves, S waves, longitudional

the difference between the arrival of the two waves can be used to calculate the epicenter and the focus of the earth quake but several siesmograpsa at different locations are needed to determine this.

Magnitude: is related to the amount of ground motion.

Richter magnitude scale: a scale commanly used in the U.S. when reporting earth quakes. used to measure the magnitude the scale is logarthmic so that the increases from 1 # TO THE next are exponential

the richter scale reflects both ground displacement and energy realesed:

movement from one whole number to the next represents:

a ground movement 10 x greater than the previous #

and an energy level 30 x greater then the previous #

frequency of earth quakes

magnitude # per year

over 8 1 or 2

7-7.9 18

6-6.9 120

5-5.9 800

4-4.9 6,200

3-3.9 49,000

2-2.9 300,000

intensity: another way of measuring an earthquakes effects is to measure its effects on people. and surface features

Modified Mercalli Scale: measures effects on humans, a low richter scale earth quake could still rate high on this.

human methods of prevention:

release energy

structral improvements

forecasting

Ground failure:

liquifaction when wet soil is jarred allow ing water to seep between molecules and the land becomes very lubricated and unstable

land slide: are serious earthquake hazard

tsunamis: large waves of water caused by siesmic disruptions, can travel at thousands of km/ hour.

fire : is a major hazard during earhtquakes

siesmic gaps: dormant sections of otherwise active fault zones are called siesmic gaps. they may contain stored up pessure that could be dangerous.

precursor phenomenon: strange signs in nature thea sometimes precede an earth quake.

earthquake cycle: concept that earthquakes may be broadly periodic and cyclical in nanture

unlocking faults: to release stored up energy was discussed as a posible method of preventing major earth quakes

fluid injection: has been shown as one possible method of causing the faults to slip and release energy.

elastic rebound: energy is stored up as rocks are compressed, and then instantly released when they finally break. and then they begin to store up energy again.

fault scarf: visible above ground risings generated by an earthquake.

Shock waves travel at 5 miles per second

Land slide scarf: caused by and earthquake