Description: This animation gives an overview of the most-recognized proponents (and opponents) of Plate Tectonics Theory up into the 1960's, with the discoveries that helped form the theories.
In the year 1596 cartographer Abraham Ortelius noted that the coastlines of Africa and South America appeared to fit together, compelling him to propose that the continents had once been joined but were pulled apart by "earthquakes and floods."
And yet, the theory of plate tectonics represents a fairly young science. The "Father of Plate Tectonics", Alfred Wegener proposed "Continental Drift" in 1912, but was ridiculed by fellow scientists. It would take another 50 years for the concept to be accepted.
Description: It was once thought that mantle convection could drive plate motions. Early textbooks showed mantle convection cells, like in a beaker of hot liquid on a Bunson burner, pushing plates along from below. Convection in the mantle, certainly plays a role, but doesn’t explain how some plates move faster than the convective currents beneath them. What would cause that? Current dynamic models have plates moving as part of a gravity-driven convection system that pushes young hot plates away from spreading ridges and pulls old cold plates down into subduction zones.
Description: This intermediate-level animation describes what the tectonic (lithospheric) plates are and how they interact. It differentiates between continental and oceanic plates, and between the three major types of boundaries.
The cool, rigid outer layer of Earth is highly fractured. In most places, huge chunks or pieces of this rigid outer layer, called plates, are in continuous motion. Plates can range from 50 km to 200km thick. Continental plates are thicker and less dense than oceanic plates that are formed at spreading ridges.
Viewers will learn to define a tectonic or lithospheric plate; differentiate between continental and oceanic plates; differentiate between the 3 types of plate boundaries; and learn about the generalized seismicity associated with boundaries.
1) What forces are acting on the earth that result in different types of plate boundaries?
2) Can you name three basic types of faults?
3) Is a reverse fault caused by tension, extension or shearing?
Description: All buildings have a natural, period, or resonance, which is the number of seconds it takes for the building to naturally vibrate back and forth. The ground also has a specific resonant frequency. Hard bedrock has higher frequencies softer sediments. If the period of ground motion matches the natural resonance of a building, it will undergo the largest oscillations possible and suffer the greatest damage. A classroom demonstration follows the animated portion of this video clip.
For more resources that support this animation, visit: http://www.iris.edu/hq/inclass/animation/224
Description: Scientists have developed far-more sensitive seismometers that, with faster computers, have enabled them to record & interpret a broader spectrum of seismic signals than was possible in the 1930's, when the Richter magnitude was developed. The moment magnitude uses seismograms plus what physically occurs during an earthquake (which can also be derived from seismograms), known as the "seismic moment". (For related resources, please visit: http://www.iris.edu/hq/inclass/animation/205 )
Description: Earth’s interior is broadly grouped into three main layers on the basis of chemical composition: crust, mantle, and core. An egg analogy is used to show relative thicknesses, and a Big Hunk analogy illustrates how a material of a single composition can be either brittle or ductile depending on temperature. This animation shows briefly how scientists figured out where these layers were, what the layers are, and how the crust is often mistaken for the tectonic (aka lithospheric) plates.
Description: A volcanic "hotspot" is an area in the mantle from which heat rises as a thermal plume from deep in the Earth. High heat and lower pressure at the base of the lithosphere (tectonic plate) facilitates melting of the rock. This melt, called magma, rises through cracks and erupts to form volcanoes. (for related resources visit: http://www.iris.edu/hq/inclass/animation/136 )
Description: New oceanic crust is created at this boundary when basalt magma, formed in the mantle, rises into fractures in the crust and solidifies. Spreading ridges are high elevation because the young oceanic plate at the ridge crest is hot and less dense than the older, colder and more dense plate on the flanks of the ridge. (for related resources visit: http://www.iris.edu/hq/inclass/animation/90 )
Description: Seismic tomography is an imaging technique that uses seismic waves generated by earthquakes and explosions to create computer-generated, three-dimensional images of Earth's interior. Human CAT scans are often used as an analogy. Here we simplify things and make an Earth of uniform density with a slow zone that we image as a magma chamber.
Description: Video lecture demonstrates the use of foam faults to demonstrate faults, and a deck of cards to demonstrate folds and fabrics in rock layers. Different types of faults include: normal (extensional) faults; reverse or thrust (compressional) faults; and strike-slip (shearing) faults.
For related resources, please visit: http://www.iris.edu/hq/inclass/video/54.
Description: Silly Putty is used as a model to show how the asthenosphere is elastic when exposed to short-duration forces (like seismic waves) but plastic when exposed to long-duration forces (like the load of the Hawaiian Islands on the Pacific Plate).
Description: Video lecture of Dr. Robert Butler, University of Portland speaking to middle-school teachers about elastic rebound and brittle material using a yardstick as a mechanical analog for the lithosphere. The yardstick is a brittle material that has elastic properties, yet, like the lithosphere, is capable of generating earthquakes.
Description: Video lecture on how temperature controls mechanical behavior of materials, including rocks. A Big Hunk candy bar is used as a model. The cold candy bar is brittle whereas the warm candy bar is ductile or "plastic".
Description: Video lecture on divergent (spreading), transform (strike-slip), and convergent (subduction and continental collision) types of plate boundaries. Recorded during a 2007 teacher workshop on earthquakes and tectonics. Speaker is Dr. Robert Butler, University of Portland Oregon
Description: Conceptual model of the relative thicknesses of the Lithosphere relative to the diameter of the Earth uses a hard-boiled egg to gain understanding about the scale of the lithospheric plates. (for related resources, visit: http://www.iris.edu/hq/inclass/video/101)
Description: A travel time curve is a graph of the time that it takes for seismic waves to travel from the epicenter of an earthquake seismograph stations varying distances away. The velocity of seismic waves through different materials yield information about Earth's deep interior. Seismic waves "bounce" the buildings to merely to illustrate arrival times and wave behavior, not to depict reality. The resultant seismograms show that stations around the world record somewhat predictable arrival times.
Description: A travel time curve is a graph of the time that it takes for seismic waves to travel from the epicenter of an earthquake seismograph stations varying distances away. The velocity of seismic waves through different materials yield information about Earth?s deep interior. IRIS? travel times graphic for the 1994 Northridge, CA earthquake is animated to show how travel times are determined. (For related resources, please visit: http://www.iris.edu/hq/inclass/animation/120 )
Description: n this animation, we are showing an ocean/continent convergent boundary at the leading edge of the plate. We see the denser oceanic plate diving beneath the continental plate. The down-going oceanic plate eventually warms up to the temperature of the surrounding mantle. Such destruction (recycling) of oceanic plates occurs along convergent boundaries where plates collide and an oceanic plate is subducted. For additional resources, please visit: http://www.iris.edu/hq/inclass/animation/89
Description: Video lecture on divergent (spreading), transform (strike-slip), and convergent (subduction and continental collision) types of plate boundaries. Recorded during a 2007 teacher workshop on earthquakes and tectonics. (For additional resources, please visit: http://www.iris.edu/hq/inclass/video/106 )