Types of Faults and Types of Faults and seismic wavesseismic waves

What is a fault?What is a fault?

A A faultfault is a break in the rocks that is a break in the rocks that make up the Earth’s crust, along make up the Earth’s crust, along which rocks on either side have which rocks on either side have moved past each other. moved past each other.

The direction of movement along the The direction of movement along the fault plane determines the fault type.fault plane determines the fault type.

GEOLOGICAL CONCEPTSGEOLOGICAL CONCEPTSTYPES OF FAULTTYPES OF FAULT

Footwall/Hanging wall from Mining geologyFootwall/Hanging wall from Mining geology

Miners put their lamps on the hanging wall and walk on the foot wall.

Three major FaultsThree major Faults

Strike-slip

Reverse

Normal

Normal FaultNormal Fault

The hanging wall moves down relative to the foot wall.

This fault type is caused by tensional stress.

Normal FaultNormal Fault

Normal FaultNormal Fault

Normal FaultNormal Fault

Reverse FaultReverse Fault

The hanging wall moves up relative tothe foot wall.

This fault is caused by Compressional stress.

Reverse FaultReverse Fault

Reverse FaultReverse Fault

Reverse FaultReverse Fault

Strike-Slip FaultStrike-Slip FaultThe fault exists between two pieces of crust and the Movement occurs horizontally where the sides slide past each other.

This fault type is caused by shear stress.

Strike-Slip FaultStrike-Slip Fault

Strike Slip FaultStrike Slip Fault

Strike-Slip FaultStrike-Slip Fault

Fault Movement = EarthquakesFault Movement = Earthquakes

An earthquake is caused by a sudden slip An earthquake is caused by a sudden slip on a fault. The tectonic plates are always on a fault. The tectonic plates are always slowly moving, but they get stuck at their slowly moving, but they get stuck at their edges due to friction. When the stress on edges due to friction. When the stress on the edge overcomes the friction, there is the edge overcomes the friction, there is an earthquake that releases energy in an earthquake that releases energy in waves that travel through the earth's crust waves that travel through the earth's crust and cause the shaking that we feel. and cause the shaking that we feel.

Focus- where the slip happens below ground

Epicenter-where the shaking is first felt above ground directly above the focus.

Slippage along fault initiates seismic Slippage along fault initiates seismic waves in all directions radiating from waves in all directions radiating from the focus.the focus.

Seismic wavesSeismic waves are vibrations that are vibrations that travel through the Earth carrying the travel through the Earth carrying the energy released during earthquakes energy released during earthquakes

There are two categories of seismic There are two categories of seismic waves:waves:

Body Waves: Can travel through Body Waves: Can travel through Earth’s inner layers (core, mantle, Earth’s inner layers (core, mantle, crust)- crust)-

Primary and Secondary wavesPrimary and Secondary waves

Surface Waves: Can only travel Surface Waves: Can only travel through the surface layers (crust)through the surface layers (crust)

Love and RayleighLove and Rayleigh

Primary WavesPrimary Waves

P waves- are the first waves to arrive at a seismograph station.

-fastest form of wave, sometimes called compression waves.

- Can move through both liquids and solids.

- These waves cause rock particles to move back and forth in the same direction as the wave is traveling (push-pull).

S-Waves-S-Waves- arrive after the primary arrive after the primary waves at the seismograph station. waves at the seismograph station.

-Can travel through solids only. -Can travel through solids only.

-Cause particles to move back and -Cause particles to move back and forth at right angles to the line of forth at right angles to the line of wave movementwave movement

Secondary WavesSecondary Waves

SEISMOLGYSEISMOLGYEARTHQUAKE LOCATIONEARTHQUAKE LOCATIONTravel time versus distance plotsTravel time versus distance plots

Can construct distance versus Can construct distance versus travel time for earthquakes travel time for earthquakes knowing properties of knowing properties of earth’s interiorearth’s interior

Note that with increasing Note that with increasing distance the arrival times distance the arrival times for the various waves for the various waves separates.separates.

The 3 min 45 sec difference The 3 min 45 sec difference between the arrival time of between the arrival time of the P and S waves the P and S waves corresponds to a distance of corresponds to a distance of 2000 km.2000 km.

SEISMOLOGYSEISMOLOGYLOCATING EARTHQUAKESLOCATING EARTHQUAKESTriangulationTriangulation -Need three different -Need three different

seismic stations to locate seismic stations to locate an earthquake.an earthquake.

-Measure the P-S arrival -Measure the P-S arrival times and convert these times and convert these to distance.to distance.

-Triangulate using radius -Triangulate using radius given by P-S travel times.given by P-S travel times.

-Triangulation for position of -Triangulation for position of an earthquake near New an earthquake near New Madrid using stations in Madrid using stations in Columbus, St Louis and Columbus, St Louis and MemphisMemphis

Surface WavesSurface Waves

Rayleigh waveRayleigh wave--surface wave causing the ground to shake in an elliptical motion

Because of its motion, it moves the ground up and down, and side-to-side in the same direction that the wave is moving

Most of EQ shaking is due to this type of wave

Love wave- Love wave- produce entirely horizontal motion

Moves the ground side-to-side Named after A.E.H. Love a British

mathematician

http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm#Particle_Motion

Measuring EarthquakesMeasuring Earthquakes

Magnitude-Magnitude- the amount of energy the amount of energy released during an EQreleased during an EQ

Richter Scale-Richter Scale- based on the largest based on the largest seismic waves generated by the EQ seismic waves generated by the EQ on a factor of 10.on a factor of 10.

Moment Magnitude Scale-Moment Magnitude Scale- considers considers the size of the fault rupture, the the size of the fault rupture, the amount of movement, and rock’s amount of movement, and rock’s stiffnessstiffness

Modified Mercalli ScaleModified Mercalli Scale

Measures the intensity of the EQ using Measures the intensity of the EQ using a rating system of the damagea rating system of the damage

Scientists compile information from Scientists compile information from various observers within different zip various observers within different zip codes to get a better understanding codes to get a better understanding of the devastation caused by an EQ of the devastation caused by an EQ to determine its intensity.to determine its intensity.