VocabularyEarthquakes • Focus – the area along a fault at which slippage first occurs, initiating an earthquake. • Epicenter – the point on Earth’s surface directly above the focus.
VocabularyEarthquakes • Seismic waves – waves of energy that travels through the earth as a result of earthquakes, explosi on or heavy impact on Earth. • Kinds of Seismic Waves: • P waves • S waves • Surface waves
VocabularyEarthquakes • P waves – Primary Waves; the longitudinal waves generated by an earthquake. • S waves – secondary waves; the transverse waves generated by an earthquake.
VocabularyEarthquakes • Surface waves – Surface waves are analogous to water waves and travel along the Earths surface.
What Are Earthquakes• Earthquake - A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earths crust or volcanic action.
What Are Earthquakes• Occur mostly at the boundaries of tectonic plates when plates shift.• Rocks along edges of tectonic plates experience immense pressure.
What Are Earthquakes• Rocks break as stress becomes so great.• Energy is released as seismic waves when rocks break along fault line.
What Are Earthquakes • The exact place where the rocks first break where the earthquake originates is called the focus. • The Point on the surface directly above the surface is called the epicenter.
Energy is transferred by waves • P waves also known as longitudinal waves, move faster through rocks than other seismic waves. • So they are the first waves experienced
Energy is transferred by waves • P waves travel by compressing Earth’s crust in front of it and stretching the crust behind it.
Energy is transferred by waves • S waves are also known as transverse waves. • They move more slowly through Earth. • Thus called secondary waves (S waves)
Energy is transferred by waves • S waves motion is like that of a rope shaken up and down and/or side to side.
VocabularyEarthquakes • Seismology – the study of earthquakes and related phenomena. • Seismologist – a person studying seismology
VocabularyEarthquakes • Richter scale – a scale that express the relative magnitude of earthquakes. • Seismograph – a machine that records earthquake data.
17.2 Kind of Volcanoes • Shield Volcano Magma rich in iron and magnesium Very fluid Lava flows great distancesEruption mildEruption occur several timesLava produces gently sloping mountain
17.2 Kinds of Volcanoes• Composite VolcanoMade up of alternating layers of ash, cinders and lavaMagma is thickerGases are trapped in the magma making explosive eruptionsTypically thousand meters highSteeper cones than shield volcanoes
17.2 Kinds of Volcanoes• Cinder ConeSmallest and most abundant volcanoesTend to be active for a short time then become dormant Vast quantities of ash and lava fall around vent that form the cone Gas-trapped magma – explosive eruption
17.2 Earthquakes and Volcanoes• Kinds of Volcanoes