Earthquakes Chapter 6 Section 1

Section 6.1 – Earthquakes and Plate Tectonics Earthquakes occur when rocks under stress suddenly shift along a fault. The rocks from both sides of the fault are pressed together and cannot move. When the stress becomes to great the rocks will suddenly grind past each other

Section 6.1 – Earthquakes and Plate Tectonics The elastic rebound theory says that rocks are stressed and will break at their weakest point and spring back to their original shape. As they break and move they release seismic waves The seismic waves cause other rocks to break and spring back. These are known as aftershocks

Section 6.1 – Earthquakes and Plate Tectonics The area of the fault where the first slippage occurs is the focus The point on the earth’s surface above the focus is called the epicenter

Section 6.1 – Earthquakes and Plate Tectonics 90 percent of continental earthquakes have a shallow focus within 70 km of the surface (about 44 miles) Intermediate focus earthquakes are between 70 km and 300 km (44 miles to 186 miles) Deep focus quakes are between 300 km and 650 km (186 miles to 404 miles)

Section 6.1 – Earthquakes and Plate Tectonics Most earthquakes occur along the edges of plates. There are 3 major earthquake zones The largest is the Pacific Ring of Fire It is the border of the Pacific Plate where is touches the North and South American plates, Asian Plate, and the Australian Plate

Section 6.1 – Earthquakes and Plate Tectonics The second major zone is along the mid-ocean ridges. The third major zone is between Europe and Africa

Section 6.1 – Earthquakes and Plate Tectonics A fault zone is an area where several plates are touching The San Andreas Fault is actually several faults that all connect to form one long fault zone

Section 6.1 – Earthquakes and Plate Tectonics Not all earthquakes happen on plate boundaries The most wide felt earthquake in the United States occurred in New Madrid, Missouri in 1812 There is an ancient fault zone deep within the North American Plate along the Mississippi River region. China also has earthquakes in the middle of the Asian plate