What are tectonic plates?

What are tectonic plates?

Tom Jordan (Director, Southern California Earthquake Center (SCEC)) gives expert video advice on: What is a geologic fault?; What is the "Richter Scale" of an earthquake?; What is the "Moment Magnitude Scale" of an earthquake? and more...

The earth's surface is broken into a number of tectonic plates. These are regions that comprise the earth's crust and the upper part of its mantel, about 1 kilometers thick, that can extend laterally for large distances. For example, the Pacific Plate occupies most of the Pacific Basin and has dimensions as large as 1, kilometers across. We have, in addition to large plates such as the Pacific Plate, the North American Plate, the Eurasian Plate, we have a number of smaller plates, which can also be significant sources of tectonic activity.