What are Earthquakes? The shaking or trembling caused by the sudden release of energy Usually associated with faulting or breaking of rocks Continuing adjustment of position results in aftershocks

What causes Earthquakes? First we have to look at the Layers of the Earth and the convections currents within.

Layers of the Earth The Earth is made of three major layers A.Crust: The surface of the Earth which is composed of a series of plates of slowly moving rock. It only has a depth of several miles.( from surface to 10 km below ocean basins or 65 km below the continents) B.Mantle: Layer of partially melted rock found in between crust and core. (about 2900 km thick) C.Core: A.Outer Core: 2250 km thick layer of liquid iron and nickel B.Inner Core: 1200 km thick layers composed of solid iron and nickel

Convection Currents Tectonic plates move about at varying speeds and in different directions atop a layer of much hotter, softer, more malleable rock called the athenosphere. One idea that might explain the ability of the athenosphere to flow is the idea of convection currents.

What Causes Convection Currents? When mantle rocks near the radioactive core are heated, they become less dense than the cooler, upper mantle rocks. These warmer rocks rise while the cooler rocks sink, creating slow, vertical currents within the mantle (these convection currents move mantle rocks only a few centimeters a year).

Convection Currents Animation

Floating Puzzle Plate Tectonics:The idea that the earth’s crust is made up of huge pieces, known as plates, that move on a top of hot liquid Pangaea: At one time all of the earth’s land fit together in one big mass. Scientists called this land Pangaea Continental Drift: The breaking apart of Pangaea into the various continents we have today and the separation of those continents.

Faults The surface of crustal plates fit into one another like the palms of your hands=> as you rub your hands together it makes a “slip-stick” movement => the earths crust will move the same way With a sudden “slip” movement of the plates an earthquake will occur Three main types of plate boundaries: –Spreading Zones=> Plates move apart –Subduction Zones=> Plates compress-one slides under the other –Transform faults=>Plates slide horizontally

Measuring Earthquakes Earthquakes produce vibrations which travel through rock in the form of waves – these waves travel outward from the focus like ripples on a pond Seismic Waves: Vibrations that travel through Earth which carry the energy released during an earthquake There are 3 categories of seismic waves: P waves, S waves, and surface waves

Seismic waves P waves: Primary wave or P waves are the first waves to arrive. They compress and expand like an accordion. Can travel through both solids and liquids. Cause buildings to expand and contract. S waves: Secondary waves are S waves are the second wave to arrive. They vibrate side to side as well as up and down. Can only travel through solids. This causes structures to shake violently. Surface waves: These waves travel more slowly then P waves and S waves but can produce more severe ground movements (transverse waves).

Body Waves: P and S waves Body waves P or primary waves –fastest waves –travel through solids, liquids, or gases –compressional wave, material movement is in the same direction as wave movement S or secondary waves –slower than P waves –travel through solids –shear waves - move material perpendicular to wave movement

Surface Waves: R and L waves Surface Waves –Travel just below or along the ground’s surface –Slower than body waves; rolling and side-to-side movement –Especially damaging to buildings

Detecting Seismic Waves To record and measure the vibrations of seismic waves, geologists use instruments called seismographs. A seismograph records the ground movements caused by seismic waves as they move through the earth. There are 3 different scales which may be used to measure an earthquakes’ intensity. –Mercalli Scale –Richter Scale –Moment Magnitude Scale

The Focus and Epicenter of an Earthquake The point within Earth where faulting begins is the focus, or hypocenter The point directly above the focus on the surface is the epicenter As the earth shakes a break occurs in the rock layer of the earth this is known as a fracture. If the rocks on either side of a fracture move we call this a fault.

How is an Earthquake’s Epicenter Located? Three seismograph stations are needed to locate the epicenter of an earthquake A circle where the radius equals the distance to the epicenter is drawn The intersection of the circles locates the epicenter

Mercalli ScaleRichter ScaleMoment Magnitude Scale First to be developed – rate earthquakes on intensity and destruction Rates the size of a seismic wave based upon data from a seismograph Estimates the total energy released during an earthquake Not a precise measurement- description of affects of earthquakes Accurate for small nearby earthquakes but not large or distant ones Value is determined by strength and type of waves as well as damage caused One earthquake can have several ratings Replaced with invention of electronic seismographs Still in use today