What is it? San Andreas Fault, geological fault zone in California



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tarix21.06.2018
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What is it?

  • San Andreas Fault, geological fault zone in California

  • 800mi long and approx. 10mi deep

  • Right lateral strike-slip fault

  • Imperial Valley to Point Arena

  • Marks the boundary between N.American and Pacific plates

  • Movement of the plates cause earthquakes



Surface Features

  • A linear trough reveals the presence of the fault

  • The fault zone is marked by distinctive landforms

  • These include long straight escarpments, narrow ridges, and small un-drained ponds

  • Stream channels characteristically jog sharply to the right where they cross the fault



Brief History

  • The San Andreas Fault has been dated at 29 million years old

  • The greatest recorded movement at one time was 5 meters in the great San Francisco Earthquake of 1906

  • This measured an 8.25 on the Richter Scale



Major Earthquakes Along the Fault

  • 1906, San Francisco

  • Began at 5:12 am, lasted 20-25 seconds and the aftershocks lasted 45-60 seconds

  • It measured 8.25 on the Richter Scale



1906 San Francisco Quake

  • The number of deaths resulting from the quake and the fire following the quake was 3,000

  • The total number of injuries was 225,000

  • The property damage that occurred was estimated at $400million in 1906 dollars.



1952 Kern County Quake

  • Occurred on July 21, at 5 am

  • The quake measured 7.5 on the Richter Scale

  • The quake was felt from Reno, Nevada to San Diego, California



1952 Quake



1989 Loma Prieta Quake

  • Occurred October 17th, at 5 pm

  • The magnitude was estimated 7.1 on the Richter Scale

  • The quake did not come as a surprise to geologists



1989 Quake

  • The quake caused damage in San Francisco and Oakland

  • The 1989 earthquake caused:

    • $7 billion in damage
    • 12,000 displaced people
    • 3,757 injuries and 67 deaths


New Designs and Construction of Buildings in Earthquake Prone Areas

  • Buildings, homes, bridges and overpasses will be built to withstand strong shaking

  • Some cities have programs to tear down unstable buildings or homes

  • Automatic shut off of gas lines when the P-wave hits to limit fire hazards



  • Places not to build homes or buildings:

    • Ground failure areas of liquefaction
    • Landslide prone areas


Accurate Prediction of Earthquakes (A Work In Progress)

  • China has been the only country who has predicted an earthquake nine hours before, in which they saved lives

    • However, the next quake they had came unexpected
  • In Tokyo, Japan they are hard away at work trying to learn how to successfully predict earthquakes

  • Other geologists around the world are also working to find an answer to predict the quakes



Earthquake Probability

  • Research conducted since the 1989 quake helped USGS and other scientists conclude:

    • 70% probability of at least one magnitude 6.7 or greater quake
    • 21% probability of that 70% is on the San Andreas Fault
    • The quake might strike the San Francisco Bay region before 2030
    • Major quakes may occur in any part of this region
    • Communities in the Bay Area region continue to prepare for earthquakes


Earthquake Odds

  • Rates of large earthquakes in the San Francisco have dropped after the Great 1906 Earthquake.

  • San Andreas Fault slipped so much over such a great length in that quake that the strain was reduced on most faults throughout the region.

  • Strain has been slowly building up again.

  • However, level of seismic activity has not yet reached that of the late 1800's.



In Conclusion, we’ve learned:

  • The geography of the San Andreas Fault

  • A few of the major quakes on the fault

  • What everyone can do to help reduce the risk of disaster when a quake hits

  • Probability of the next big earthquake



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