In 1755, when a deadly earthquake struck the city of Lisbon, no one understood what could cause the ground to shake as it did. Observations of residents at the time indicated that the quake had delivered two distinct types of vibrations. This video segment describes the history of seismology. Topics include the two main types of seismic waves (S- and P-waves), how a seismograph works, and how seismograph ... Full description.

Although the San Andreas Fault is the longest and one of the most active fault zones in California, it is not responsible for every earthquake in the state. This video segment describes the geologic setting of the San Andreas fault and a network of other active faults, particularly thrust faults, closer to Los Angeles, and explains why these may present a greater danger to the city than the San Andreas ... Full description.

This resource provides eyewitness accounts and historical photographs from notable damaging earthquakes that have occurred in or near Santa Barbara County, California. It also contains a catalog of all earthquakes that have been felt in the greater Santa Barbara region between 1800 and 1960. Major earthquakes covered include the 1812 Santa Barbara Earthquake, the 1857 Fort Tejon Earthquake, the 1902 ... Full description.

This activity describes the technique of preparing "GIS-ready" data and shows how to map that data and conduct basic analyses using a geographic information system (GIS). First, you will download and format near real-time and historical earthquake data from the USGS. Using latitude and longitude fields, you will then plot these data in a GIS. Next, you will analyze patterns by querying records and ... Full description.

This web site provides a short, interactive, four-question quiz on earthquakes focusing the the largest earthquake in both the world and in recent US history, preparedness, and the development of seismic instrumentation. Full description.

This on-line exhibit provides an in-depth look at earthquakes. It covers the technology and history of seismographs, plate boundaries and tectonics, faults, seismic waves and their uses, the Richter and Mercalli scales, and details about California earthquakes. Full description.

This activity is designed to provide a better understanding of earthquake activity, the locations of faults, and earthquake hazards in the San Francisco bay area. Students study a false color satellite photo of the bay area on which earthquake epicenters for a seventeen year period have been plotted. Students use a California highway map or a copy of the California or San Francisco Bay area map from ... Full description.

This site contains an exercise in which students are asked to examine the frequency and distribution of earthquake epicenters and compare these epicenters to the distribution of plate boundaries and cities. Students download earthquake epicenters for the last several days and for an entire year from the Internet, and map the information using ArcView geographic information system (GIS), and analyze ... Full description.

This bulletin discusses the magnitude 7.9 earthquake that shook the islands of Tonga in May 2006. Topics include the tectonic setting of the islands, at the boundary of the Pacific and Australian plates, the frequent seismic activity at this location, how earthquakes are produced at subduction zones, and how they can reveal information about the Earth's interior. There is also information about the ... Full description.

This is a demonstration of the principle of elastic rebound for the cause and recurrence of earthquakes. Under the Elastic Rebound Theory, the continuous motion of plates on Earth causes stress to build up at the boundaries between the plates, where friction keeps the boundaries locked. Stress is continually building up, and earthquakes act to relieve that stress. In the demonstration, the two sides ... Full description.