PLATE TECTONICS
What Happens at Conservative Transverse Plate Boundaries
Conservative plate boundaries occur where two crustal plates slide past each other. Crust is neither created nor destroyed at these passive boundaries.
l Great fissures or fault lines mark the places where plates move past each other. They are called transverse faults or tear faults. The world’s most famous transform fault is the San Andreas Fault in
ey ar California in the USA. This 1,300km-long 00k l
fault marks the boundary where the Pacific and the North American plates move past each other.
l Both of these plates move in a northwesterly direction. But the Pacific Plate moves about six times faster than the North American Plate, and this causes cracks and fissures to occur in the earth’s crust. The slippage between the two plates is not smooth. Tension builds up as underground rocks jam against each other. When the rocks eventually snap, the plates suddenly lurch past each other. Shock waves are then released and they cause tremors or earthquakes when they reach the earth’s surface. The city of San Francisco in California suffered from severe earthquakes in 1906 and 1989.
You can learn more
about transverse faults on page 33.
The San Andreas Fault in California, USA
You can learn more about earthquakes in Chapter 4.
Did you know?
If the movements of the Pacific and North American plates continue as at present, 16 million years from now Los Angeles could be situated alongside San Francisco.
The Pacific Plate moves northwestwards at a rate of 6 cm a year
The North American Plate moves northwestwards at a rate of 1 cm a year
San Francisco
Pacific Ocean Plate
movement Los Angeles
A conservative plate boundary in California
12 Pacific Plate
North American Plate
9 California
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