Transcript 6.1 Earthquakes and

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.

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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
