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Faults

A fault is a crack in the surface of the earth. When pressure builds in the earth the faults are the most likely places where the pressure would be relieved, causing an earthquake. There are two major parts of a earthquake fault: Hanging wall-If you were in a cave that followed along a fault the hanging wall would be where you hung your lantern. Foot wall- If you were in a cave that followed along a fault the foot wall would be the lower part of the fault under your feet. Please wait while animations load... Normal Fault Side (A)--------Side (B) A normal fault is caused by the pulling apart of two land masses. When they are pulled apart the HANGING WALL (side B) will drop in comparison to the FOOT WALL (side A). This fault is not found in the Punchbowl area because there is too much pressure between the Pacific and North American Plates.

Reverse Fault Side (A)--------Side (B) A reverse fault is caused by the collision of two land masses. If two land masses collide the lighter in density will be pushed over the other. In the animation to the left the (side B) Is the lighter of the two, and is pushed up and over (side A). This type of fault is common in the punchbowl area because of the collision of the Pacific and the North American Plates.

Left Lateral Strike Slip Fault Side (A)--------Side (B) A left lateral strike slip fault is caused by sheer. Two land masses are sliding by each other. In this case one land mass moves LEFT in relation to the other. If you are on (side A) on the edge of the fault facing (side B) the land you were looking at would be moving left in relationship to you. Then if you stepped onto (Side B) and turned to face (side A) the land mass (side A) would be moving left in relationship to where you where standing. A good example of a Left Lateral Strike Slip fault would be the Garlock fault. On the Garlock fault the Antelope Valley moves left in relationship to the Tehachapi Mountain range.

Right Lateral Strike Slip Fault Side (A)--------Side (B) The right lateral strike slip fault Is the same as a left lateral strike slip fault, but the opposing side moves Right in relationship to the other. The San Andreas fault is a perfect example of this. The Antelope Valley (to the north of the San Andreas) moves right in relationship to the San Gabriel Mountains. The San Gabriel Mountians are moving right in relationship to the Antelope Valley.

The Mercalli scale for the intensity of earthquakes was developed in 1902 by Giuseppi Mercalli, an Italian geologist, and consists of 12 levels, depending on what an individual experiences in his or her location.

I	Not felt by people except under favorable circumstances, although dizziness or nausea may be experienced.
II	Detected indoors by some, especially on the higher floors of tall structures.
III	Felt indoors by some people, usually as a rapid vibration, but not immediately recognized as an earthquake. Vibration is akin to that of a light truck passing by.
IV	Detectected indoors by many and outdoors by a few. May awaken light sleepers but is not overly frightening. Vibration is similar to a heavy truck passing.
V	Felt indoors by just about everyone and outdoors by most. Awakens most sleepers, frightens a few.
VI	Felt by everyone, indoors and outdoors. Awakens all sleepers and frightens many. General excitement.
VII	Everyone frightened. People find it difficult to remain standing; damage done to poorly designed or constructed buildings, but little damage done to well built ordinary structures.
VIII	General fright and alarm approaching panic. Heavy furniture dances across floors, chimneys topple and stone walls fall.
IX	Panic in general. Conspicuous ground cracks, underground pipes sometimes break, wood frame houses are thrown out of plumb.
X	Panic is general. Large cracks appear in the ground and landslides happen. Even well-built structures experience damage or collapse. Railroad rails are bent.
XI	Panic is general. Large sea waves, tsunamis, are generated. Broad fissures spread across the ground and earth slumps and landslides are common place.
XII	Panic is general. Damage is total. Large rock masses are torn loose and fall, rivers deflected.