Chapter 7:Earthquakes 7.1:Forces in earth’s Crust
How does stress change Earth’s Crust? Stress in Earth’s Crust Stress can push, pull, or squeeze rock in Earth’s crust. Three kinds of stress can occur in the crust. Rocks are hard and stiff but the movement of earth’s plates can create strong forces that slowly bend or fold rocks like candy. Stress: is a force that acts on a rock to change its shape or volume
Three Types of Stress Tension: Rock can be stretched so it becomes thinner in the middle. This makes the rock act like bubble gum. This process is tension which occurs where two plates pull apart. Compression: one plate pushing against another plate can squeeze rock like a giant trash compactor. This process occurs where two plates come together. Shearing: Stress that pushes a mass of rock in two opposite directions is shearing. This can cause rock to break and slip apart or change its shape. This process occurs where two plates slip past each other.
How do Faults form? A fault is a break in the rock of the crust where rock surfaces slip past each other Faults The three main types of faults are defined by the direction in which rock moves along the fault. When enough stress builds up in the rock, the rock breaks creating a fault.
Three types of faults The rock that lies under is called the footwall The block of rock that sits over the fault is the hanging wall Reverse Faults: has the same structure as normal fault, but the block moves in the reverse direction So hanging wall moves up and footwall moves down Strike-slip Faults: the rock on either side of the fault slip past each other sideways with little up or down motion. Normal Faults: When rock is pulled apart by tension in earth’s crust, normal faults form. In a normal fault, the fault cuts through rock at an angle, so one block of rock sits over the fault, while the other lies under the fault.
How does plate movement create new landforms? How anticlines and synclines form: these terms are used to describe upward and downward folds. A fold in rock that bends upward into an arch is an anticline. A fold in rock that bends downward to form a V shape is a synclines Over millions of years, the forces of the plate movement can change a flat plain into features such as anticlines and synclines, folded mountains, fault-block mountains and plateaus How folded mountains form: The collisions of two plates can cause compression and folding of the crust over a wide area. Folding produces some of the world’s largest mountain ranges How folds are forms: folds are bends in rocks that forms when compression shortens and thickens Earth’s crust.
Homework Read Chapter 7.1 Complete Pages 223-229 This is Due Tuesday 28, 2014 Study for Quiz 7.1
Chapter 7: Earthquakes and Seismic Waves Earthquakes start below the surface of the Earth. An earthquake's seismic waves carry energy up toward the surface and down through the interior. An earthquake is shaking and trembling that the results from movement of rock beneath Earth’s surface Seismic waves are vibrations that are similar to sound waves. They travel through Earth carrying energy released by an earthquake http://www.youtube.com/watch?v=VSgB1IWr6O4
Types of Seismic Waves Like a pebble thrown into a pond, the seismic waves of an earthquake race out in every direction from the earthquakes focus This action triggers the earthquake. The point on the surface directly above the focus is called the epicenter. The focus is the area beneath Earth’s surface where rock that was under stress begins to move. Seismic Waves The diagram shows how seismic waves traveled during an earthquake along the Denali fault.
Three main categories of seismic Waves P-waves: compress and expand the ground like an accordion. S-waves: vibrate from side to side or up and down Surface-waves: move more slowly than P and S waves but they can produce severe ground movements. P, S, and Surface Waves Earthquakes release stored energy as seismic waves.
How are earthquake measured? The Richter Scale: an earthquake's magnitude is a single number that geologist assign to an earthquake based on the earthquake’s size. The amount of earthquake damage or shaking that is felt is rated using the modified Mercalli scale. The magnitude or size of an earthquake is measured on a seismograph using the Richter scale or moment magnitude scale Modified Mercalli Scale The Modified Mercalli scale uses Roman numerals to rate the damage and shaking at any given location, usually close to the earthquake. The Modified Mercalliscale rates the amount of shaking from an earthquake. A seismograph is an instrument that records and measures an earthquake’s seismic waves
The Moment Magnitude Scale Geologist use the moment magnitude scale to rate the total energy an earthquake releases. Earthquake Magnitude The table gives the moment magnitudes of some recent earthquakes http://www.youtube.com/watch?v=dJBS94GVyuo
How is an epicenter located? Locating the epicenter helps geologists identify areas where earthquakes may occur in the future Seismic Wave Speeds Seismographs at five observation stations recorded the arrival times of the P and S waves produced by an earthquake. These data were used to draw the graph. Geologist use seismic waves to locate an earthquake’s epicenter An Earthquake’s Epicenter The map shows how to find the epicenter of an earthquake using data from three seismographic stations.
Homework COMPLETE PAGE 231-237 READ CHAPTER 7.2