PLATE MARGINS AND EARTHQUAKES

Plate Margins and Earthquakes

Plate Margins and Earthquakes

Introduction

Since the early 1900s, geologists have known that the Earth is divided into three main layers: a thin outer crust, a thicker mantle, and a core. But exactly how these layers interact and what they are made of are still open to debate (Robert, 2005). The crust is the only layer that geologists can really study first-hand. So geologists have had to study other data, such as the path earthquake shock waves take as they travel through the Earth.

Plates on the Move

In the 1960s geologists developed an exciting new theory called plate tectonics. Plate tectonics proposes that the lithosphere (the crust and uppermost layer of the mantle) is not a continuous sheet of solid rock. Instead it is divided into about 12 enormous plates and many smaller plates that "float" like icebergs on the top of the asthenosphere. These plates, which can be hundreds or thousands of miles across, move relative to one another and they carry the continents and ocean basins with them as they drift about. For example, most of North America and a good part of the Atlantic Ocean are on the North American Plate. But Hawaii, part of California and Alaska, and most of the Pacific Ocean are part of the Pacific Plate (Risa, 2003).

Slippin' and Slidin'

Plate tectonics revolutionized geology because it finally explained how most major geological events occur. Geologists could see that most mountain building and earthquake and volcanic activity take place along the margins of the plates. And as they studied the ways plates interact with each other, they found that in some areas new crust is always forming, while in other areas old crust is constantly being destroyed. Here's a look at the main ways plates interact with each other to influence the ...