 stress -a force that acts on rock to change its shape or volume. 3 Types of Stress  tension -pulls on crust, stretching rock so it becomes thinner in the middle  compression -squeezes rock together until it folds or breaks  shearing-pushes rock in two opposite directions

 Type of Fault: ◦ Reverse Fault  Stress Force: ◦ Compression  Movement Along Fault: ◦ The hanging wall is moving up relative to the footwall

 Type of Fault: ◦ Normal Fault  Stress Force: ◦ Tension  Movement Along Fault: ◦ The hanging wall is moving down relative to the footwall

 Type of Fault: ◦ Strike-Slip Fault  Stress Force: ◦ Shearing  Movement Along Fault: ◦ Opposing forces cause the rock to break and move horizontally

MovementFaultType of StressBoundary Hanging wall moves down relative to footwall Normal FaultTensionDivergent Boundary Hanging wall moves up relative to the footwall Reverse FaultCompressionConvergent Boundary Opposing forces cause the rock to break and move horizontally Strike – Slip Fault ShearingTransform Boundary

 Deformation – the process by which the shape of a rock changes because of stress  Elastic Rebound – the sudden return of elastically deformed rock to its undeformed shape  What is the direct cause of earthquakes? ◦ Elastic rebound

 Seismology – the study of earthquakes  Seismic Waves – a wave of energy that travels through the Earth, away from an earthquake in all directions  Seismograph – an instrument that records vibrations in the ground and determines the location and strength of an earthquake  Seismogram – a tracing of earthquake motion that is created by a seismograph  Seismic Gap – an area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes have occurred in the past And some other important terms…  Epicenter – the point on Earth’s surface directly above an earthquake’s starting point, or focus  Focus – the point along a fault at which the first motion of an earthquake occurs

Body Waves  P waves (pressure or primary waves) arrive first, travel through liquid  S Waves (secondary waves) arrive later, can not travel through liquid

P Waves S Waves Surface Waves

 The S-P Time Method ◦ Describe how a seismograph is used to determine the epicenter of an earthquake.  p 231p 231

 What does the Richter Scale measure? ◦ The strength of earthquakes – measures the ground motion from an earthquake and adjusts for distance to find its strength  What is the magnitude of an earthquake? ◦ The strength  How are magnitude and ground motion related in the Richter scale? ◦ Each time the magnitude increases by 1 unit, the amount of ground motion increases by 10 times  What does the Modified Mercalli Intensity Scale measure? ◦ The degree to which an earthquake is felt by people and the amount of damage caused b the earthquake  Why might an earthquake have more than one intensity value? ◦ Because the effects of an earthquake vary from place to place, the intensity values are usually higher near the earthquakes epicenter