4 What are Earthquakes?The shaking or trembling caused by the sudden release of energyUsually associated with faulting or breaking of rocksContinuing adjustment of position results in aftershocks
5 Anatomy of an Earthquake Focus (or hypocentre): the center of energy release.Epicentre: the point on the ground surfaceimmediately above the focus (closest point on the surface to the focus).
6 Two kinds of waves from earthquakes • P waves (compressional) 6–8 km/s. Parallel to direction of movement (slinky), also called primary waves. Similar to sound waves. • S waves (shear) 4–5 km/s. Perpendicular to direction of movement (rope); also called secondary waves. Result from the shear Strength of materials. Does not pass through liquids.
9 The amount of damage created by an earthquake depends on several factors. The earthquake’s strengthThe kind of rock and soil that underlie an areaThe population of the areaThe kind of buildings in the areaThe time at which the earthquake occurs
10 SeismologistsSeismologists study earthquakes. They can determine the strength of an earthquake by the height of the wavy line recorded on the paper.The seismograph record of waves is called a seismogram.The Richter scale is used to calculate the strength of an earthquake.
11 Intensity and Magnitude of Earthquakes Often measured using the Richter scaleBased on the amplitude of the largestseismic waveEach unit of Richter magnitude equates toroughly a 32-fold energy increase
12 Intensity and Magnitude of Earthquakes • A measure of the degree of earthquake shaking at a given locale based on the amount of damageMost often measured by the Modified Mercalli Intensity Scale
14 What is a Volcano?A volcano is a weak spot in the crust where molten material comes to the surfaceMagma reaching the surface is called lava.A volcanic eruption is the process wherein volcanic materials such as lava, fragmented rocks or gases are emitted or ejected through a crater, vent or fissure on to the earth's surface to form new deposits.
15 Volcanic TermsA volcano not known to have erupted within modern history is classified as an extinct volcano.A volcano that has been known to erupt within modern times but is now inactive is classified as a dormant volcano.An active volcano is one that erupts wither continually or periodically
17 Where do volcanoes occur? Volcanoes occur most frequently at plate boundaries.Some volcanoes, like those that form the Hawaiian Islands, occur in the interior of plates at areas called hot spots .The greatest number of volcanoes occur on the ocean floor along spreading ridges.Over 80% of those on land occur at edges of continents, or subduction zones, where one plate dives, or subducts, under another plate.
19 Why do volcanoes occur?Temperatures in the mantle are hot enough to melt rock into magma magma.•Less dense than the solid rock around it, magma rises and some of it collects in magma chambers magma chambers.•As the magma rises, pressure decreases allowing trapped gasses to expand and propel the magma through openings in the Earth’s surface causing an eruption.
23 What Erupts from a Volcano? Pyroclastic materialRock fragments created by eruptionsmagma explodes from volcano and solidifies in the airexisting rock is shattered by powerful eruptionsEXPLOSIVELapilliVolcanic bombsVolcanic blocksVolcanic ash