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1. FREQUENTLY ASKED QUESTIONS
2. NATURAL HAZARDS
What is the relationship
between faults and
earthquakes? What happens to
a fault when an earthquake
occurs?
Earthquakes occur on faults - strike-slip earthquakes occur on strike-slip faults, normal
earthquakes occur on normal faults, and thrust earthquakes occur on reverse or
thrust faults. When an earthquake occurs on one of these faults, the rock on one side of
the fault slips with respect to the other. The fault surface can be vertical, horizontal, or
at some angle to the surface of the earth. The slip direction can also be at any angle.
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What is a fault and what are the different types?
A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the
blocks to move relative to each other. This movement may occur rapidly, in the form of
an earthquake - or may occur slowly, in the form of creep. Faults may range in length
from a few millimeters to thousands of kilometers. Most faults produce repeated
displacements over geologic time. During an earthquake, the...
link
What is a "Quaternary" fault?
A Quaternary fault is one that has been recognized at the surface and that has moved in
the past 1,600,000 years (1.6 million years). That places fault movement within the
Quaternary Period, which covers the last 2.6 million years.
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Where can I find a fault map of the United States? Is one available in GIS format?
An online map of United States Quaternary faults (faults active in the last 1.6 million
years which places them within the Quaternary Period) is available via the Quaternary
Fault and Fold Database. There is an interactive map application to view the faults
online and a separate database search function. KML (Google Earth-type) files and GIS
shape files are also available for download from the...
link
How do I find the nearest fault to a property or specific location?
If you are looking for faults in California use: How Close to a Fault Do You Live? (Bay
Area Earthquake Alliance) For faults in California and the rest of the United States (as
well as the latest earthquakes) use the Latest Earthquakes Map: click on the "Basemaps
and Overlays" icon in the upper right corner of the map. check the box for "U.S. Faults".
mouse-over each fault to get a pop-up window...
link
How do I find fault or hazard maps for California?
An online map of faults (Quaternary Fault and Fold Database of the United States) that
includes California is in the Faults section of the Earthquake Hazards Program website.
Choose the Interactive Fault Map, or download KML files and GIS shapefiles from the
links on the page. USGS hazard maps, data, and tools for California and other parts of
the United States are in the Seismic Hazard Maps and...
link
Why are there no faults in the Great Valley of central California?
The Great Valley is a basin, initially forming ~100 million years ago as a low area
between the subducting ocean plate on the west (diving down under the North American
plate) and the volcanoes to the east (now the Sierra Nevada mountains). Since its
formation, the Great Valley has continued to be low in elevation. Starting about 20
million years ago the tectonics changed in California and instead...
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Why are there so many earthquakes and faults in the Western United States?
This region of the United States has been tectonically active since the supercontinent
Pangea broke up roughly 200 million years ago, and in large part because it is close to
the western boundary of the North American plate. Since the formation of the San
Andreas Fault system 25-30 million years ago, the juxtaposition of the Pacific and North
American plates has formed many faults in California...
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Why are there so many faults in the Quaternary Faults Database with the same
name?
Many faults are mapped as individual segments across an area. These fault segments are
given a different value for name, number, code, or dip direction and so in the database
each segment occurs as its own unique entity. For example, the San Andreas Fault has
several fault segments, from letters a to h, and fault segment 1h has segments with age
of last fault movement from historic (<150 years) to...
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