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In
the Great 1906 magnitude (M) 7.8 earthquake, nearly 300
miles (480 km) of the San Andreas Fault ruptured,
producing strong shaking along all of coastal northern
California. Shaking was most intense in Santa Rosa and
San Francisco. In San Francisco, broken water mains kept
firefighters from battling the fires that swept through
the city and contributed to the devastation shown in this
photograph (looking south) taken from a tethered balloon
5 weeks after the earthquake.
For
more information go to:
http://neic.usgs.gov/neis/plate_tectonics/rift_man.html
http://pubs.usgs.gov/gip/earthq3/
History
Shows That Damaging Earthquakes Have Occurred Throughout
the Bay Area...
In
the last half of the 1800s, damaging earthquakes
(magnitude 6 or greater) occurred in the San Francisco
Bay region on average every 4 years. However, this
changed in 1906:
- On
April 18, 1906, the San Andreas Fault ruptured
violently over a length of 300 miles, causing damage
from San Juan Bautista north as far as Eureka. This
magnitude 7.8 earthquake&emdash;the "Great San
Francisco earthquake"&emdash;relieved stresses on
faults throughout the bay region.
- Because
fault stresses were reduced, the rate of large quakes
in the San Francisco Bay region dropped abruptly after
the 1906 earthquake.
- The
three-quarters of a century following the 1906 quake
was a golden age for the bay region, in which urban
areas and population expanded rapidly during a time of
minimal quake activity.
- Although
the level of seismic activity has not yet reached that
of the late 1800s, since 1906 stresses on Bay Area
faults have been building up once again. The area can
expect more frequent and stronger earthquakes in the
future.
Fault
Rupture Lengths for Historical Quakes in the Bay
Area
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