Ground Deformation: Faulting and Folding Earthquakes and Mountain- Building

Seismic Waves Seismology The study of the propagation of mechanical energy: released by an earthquake and explosions through the Earth is known as Seismic waves When energy is released in this fashion, waves of motion (like the effect of a pebble tossed into a pond) are set up in the rocks surrounding the source of the energy (the focus). Seismic Waves Waves are started because of initial tension or compression in the rock which is known as stress. Instruments used to measure these waves are called seismographs.

Key Earthquake Terms Earthquake: The rapid vibration of the Earth’s surface created by the sudden movement of rock bodies past each other along a fault. Fault: The place where there is movement on the Earth’s surface. (faults come in all scales from mm to kilometers in length) Focus: The site of initial rupture, this generally occurs below the Earth’s surface. Epicenter: The point on the Earth’s surface directly above the Focus.

Energy released radiates in all directions from its source, the focus Energy from an earthquake propagates in the form of seismic waves

L-wave

Seismographs are very sensitive instruments around the world that record the event(s) (Earthquakes)

Seismograph

What is a Fault or Fault line?

A Fault is a fracture in rock along which displacement has taken place- associated with a plate boundary. Faults can be active or inactive, and can be associated with either current or old plate boundaries.

Types of Faults

Normal

Reverse

Normal Faults Reverse Faults

Strike-slip

What causes an Earthquake??

So, how does energy released by slippage at a fault travel through the ground?

Detecting and Locating Earthquakes

L-wave

Surface Waves

Energy from an Earthquake travels in seismic waves.

How far is the epicenter of an earthquake from a seismic station, if the difference between the arrival time of the P and the S wave is 5 minutes?

The P-Wave Shadow Zone P-waves travel through the liquid outer core bend, leaving a low intensity shadow zone 103 to 143 degrees away from the source, here shown as the north pole HOWEVER, P-waves traveling straight through the center continue, and because speeds in the solid inner core are faster, they arrive sooner than expected if the core was all liquid. Behavior of waves through center reveal Earth’s Interior

The S-Wave Shadow Zone Since Shear (S) waves cannot travel through liquids, the liquid outer core casts a larger shadow for S waves covering everything past 103 degrees away from the source.

Folding

Folding creates non-volcanic mountains

Folded Mountains

Fault-Block Mountains

Domed Mountains

Normal Faults Reverse Faults