This demonstration of the magnetic field lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magnetic field of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet. Full description.

The Curie temperature for iron is reached at about 20 km depth in the Earth, and the temperature is much higher at the outer boundary of the Earth's core so that the iron there is no longer ferromagnetic (the electron spins in the iron can no longer align). This demonstration will help students understand the magnetic field of the Earth, and can help explain the variation of the direction of the field ... Full description.

This demonstration of the Earth's magnetic field requires a DC motor, ammeter, electromagnet, and DC power supply or battery. The site explains the concept of a dynamo and how if an electrical conductor is in motion within a magnetic field, a current will be generated in the conductor, and if that current flows around in a loop, it will, in turn, generate a magnetic field. Full description.

In this activity, students work in teams to locate the epicenter of an earthquake using the time travel difference between the primary (P) and the secondary (S) waves. Teams work out that the time difference between the wave arrival times depends upon the distance of the monitoring station from the epicenter. To locate the earthquake they draw circles of the appropriate (scaled) radius from the monitoring ... Full description.

In this activity, students use magnetic field data and a map of the ocean floor around Iceland to observe how the direction of magnetization of the ocean floor varies. This links the magnetization of rocks with the theory of tectonic plates. As students complete the worksheet they will discover that the magnetic field of the Earth has flipped (the N pole becoming the S pole, and vice versa) many times ... Full description.

This demonstration shows how the Earth's magnetic field has flipped (the N pole becoming the S pole, and vice versa) many times through geological time. It also demonstrates that as tectonic plates move apart, new rock is formed and locks in the direction of the magnetic field at the time. Students should realize that the discovery of stripes of alternately normal and reversed-magnetized rocks forming ... Full description.

This report describes how the work of K. Wadati, Charles F. Richter, Harry O. Wood, and Beno Gutenberg resulted in a way of rating earthquakes in southern California according to an instrumental analysis of the amount of energy they released in the form of seismic waves. This work resulted in the first use of the term "magnitude" for describing the amount of energy released by an earthquake, and in ... Full description.

This report describes how measurements of earthquake magnitude, as quantified by the Richter Scale, have gradually replaced measurements of intensity, as characterized by the Modified Mercalli scale. Topics include the advantages of the Richter Scale, such as open-endedness, its purely instrumental measure which doesn't require observers' reports, and its usefulness for measuring earthquakes located ... Full description.

Recordings on this site present 164 aftershocks as they were heard at one seismic recording station. They occurred after an earthquake with a magnitude of 6.2 beneath and near New Zealand. All events are heard in rapid sequence, without the true time intervals between them. The main shock was at a depth of 30 kilometers, 10 kilometers below the interface between the subducting Pacific Plate and the ... Full description.

Data collected by a new seismic observatory at the Amundsen-Scott South Pole Station indicate that it is the quietest listening post on the planet for observing shudders produced by earthquakes around the world as they vibrate through the Earth. The South Pole Remote Earth Science Observatory (SPRESO) is located eight kilometers (five miles) from the South Pole and the new seismometers were installed ... Full description.