Earthquakes Chapter 8 Earthquakes What is an earthquake

Earthquakes Chapter 8

Earthquakes ► What is an earthquake? § (def. ) Vibration of Earth produced by a rapid release of energy ►Usually along cracks in the earth called faults ► Earthquakes usually do not “occur” on the surface ► The point where an earthquake occurs is called the focus ► The epicenter is the location DIRECTLY above the focus

Earthquakes ► What causes earthquakes? § Rocks in Earth’s crust is stressed and pulled § This action stores elastic energy ► Once the build up of energy exceeds the strength of the rock the energy is released ► The energy is released as seismic waves

Earthquakes ► Types of seismic waves ► Surface Waves § Travel along the surface of the earth § Move side-to-side AND up and down ► Body Waves § Travel through Earth’s interior

Earthquakes ► Two types of Body Waves: P and S ► P Waves (Primary waves) § Compression waves since they push and pull rocks § Fastest moving seismic wave § Able to move through solid rock and fluids ►S Waves (Secondary waves) § Slower than a P wave § Can ONLY move through solid rock ►A seismograph is used to detect seismic waves

Earthquakes

Earthquakes

Earthquakes ►A typical seismogram of an earthquake:

Richter Scale ► The Richter scale measures the magnitude of an earthquake § Magnitude refers to the size of seismic waves ►A tenfold increase in wave amplitude (height) is equal to an increase of 1 on the scale ► Draw back: only useful for shallow earthquakes

Continental Drift ► German meteorologist, Alfred Wegener, proposed a radical idea: continental drift ► Wegener noticed the continents seemed to fit together like pieces of a puzzle ► He proposed the continents are “floating” on the molten mantle and were once joined together ► This Supercontinent was known as Pangaea

Continental Drift ► Scientists dismissed his theory ► Wegener argued that the same fossils are found on different landmasses ► Ex. – Mesosaurus on Africa and S. America

Continental Drift ► More supporting evidence: ► Similar rock types and structures § Appalachian Mountains were once a large mountain chain like the Rockies § The same types of rocks that are found in North Carolina to NY are found in northern Britain and Scandinavia

Continental Drift ► The continents of North America, Europe, and Asia were known as Laurasia ► South America, Africa, India, Antarctica, and Australia were known as Gondwanaland ► The ocean south of Asia was called the Tethys Sea ► The rest of the water on Earth was called Panthalassa § The remnants of this ocean is the Pacific

► Panthalassa Gondwanaland Laurasia

Seafloor Spreading

Seafloor Spreading ► Seafloor spreading refers to the process by which plate tectonics produce new oceanic crust ► Where is this taking place? § Atlantic Ocean § Eastern Africa?

Seafloor Spreading ► Rift valleys are found along the center of the mid-ocean ridges. § Place where magma is forced upwards ► Oceanic ridges areas where the seafloor is elevated due to seafloor spreading ► The seafloors are spreading at a rate of 5 cm/year ► This means the ocean basins are no older than 200 million years old