CH. 8: Earthquakes and Volcanoes 8.1: Earthquakes

1. 8.1: I CANS: I can explain how earthquakes are caused by a buildup of strain in Earth’s crust. I can identify the type of stress associated with each fault. I can compare & contrast the seismic waves produced by an earthquake. I can recognize earthquake hazards & how to prepare for them.

Elastic Rebound: Imagine you bend a stick with force. There is only so much pressure you can apply to the stick before it is changed permanently (broken). If you apply only a small amount of force to the stick and then release, it will go back to its normal position. 2. Elastic Rebound: Is the snapping back, or the return of an object to its original position after pressure is released.

Release of Energy/Earthquakes Imagine that you continue to bend the stick every day with a small amount of force. Over time, the stick will become strained even if it does not break. The longer it has been strained, the more powerful the vibrations will be in the stick when it finally snaps and breaks. 3. The same thing happens in the case of an earthquake. An earthquake is a vibration caused by breaking and moving rock.

Faults: We learned in chapter 7 that earthquakes occur at tectonic plate boundaries. Tectonic plates slide past each other due to convection currents inside the earth’s crust. Earthquakes can also occur near the boundary of a plate, in the area called a FAULT. 4. Fault: The fault is an area where the rocks are moving and breaking. When the rock moves, it creates a gap in the crust.

Picture of a Fault:

Types of Faults: All faults are not exactly the same. There are three main types of faults: normal, reverse and strike-slip. The type of fault depends on the type of stress or pressure that is put on the rock.

Types of Faults: 5. (TABLE) Normal Fault: Rocks are pulled apart by tension forces. Rock above the fault moves down compared to rock below. Reverse Fault: Rocks are compressed (or pressed together). Compression can cause rock above a fault to move up compared to rock below. Strike-Slip Fault: (Left lateral or right lateral): Rocks are sheared (broken off) and the force causes rock on either side to move past each other in opposite directions. This looks similar to plate movement at transform boundary.

5. Faults (table):

Making Waves: 6. Strain Energy: When the rocks move, they bend. Strain energy is potential energy that builds up in the rock when bent. When released, the energy moves outward from the fault in the form of seismic waves. 7. When an earthquake occurs, seismic waves (also called earthquake waves) are transmitted. Basically, the seismic waves are the reason why areas away from the fault can FEEL the earthquake.

Focus/Epicenter: 8. Focus: The focus of an earthquake is the point inside earth where movement first occurs. It is actually located deep inside earth’s crust/upper mantle. 9. Epicenter: The point on earth’s surface located directly above the focus.

Parts of an Earthquake:

Kinds of Seismic Waves: 10. There are 3 different kinds of seismic (earthquake) waves. Surface Waves: These waves travel at shallow depths along earth’s surface. They are the slowest and largest of all types of seismic waves. These are the waves that cause the most destruction and damage to structures during an earthquake. These waves roll, sway, vibrate. P-Waves (also called primary waves/Push-pull): Travel inside earth’s surface. Cause particles particles in the rock to vibrate in the same direction the waves are moving. P- Waves travel the fastest. Because they travel the fastest, they are able to go through solids and liquids inside earth’s layers. S-Waves:

Kinds of Seismic Waves: S-Waves (also called secondary waves/Side-to-side): Move through rock material, causing particles in the rock to move at right angles to the direction that the waves are moving. S- waves can only travel through solids inside earth.

Seismic Slinky:

Learning From Earthquakes Earthquakes 11. Seismologists: are scientists who study earthquakes and seismic waves. Seismograph: An instrument used to get a record of seismic waves all over the world. 12. The magnitude of an earthquake is shown in the height of the lines it records. Richter Scale: Tells magnitude of earthquake. 13. Tsunami: Seismic sea waves caused by earthquakes.

Earthquake Safety: 14. Seismic safe: A building that will be able to stand up against the vibrations caused by most earthquakes. Is your home seismic safe? Move heavy objects to lower shelves, secure gas hot water heater and appliances. Keeping yourself safe in event of earthquake: move away from windows and to an interior wall. Even with newer technology, there is not yet a way to predict earthquakes.