At that point, the fault's most active branch moves to a spot out in the valley floor, near Cottonwood Mall. It runs northward roughly along 1300 East to about 100 South in downtown Salt Lake City, then east to University Hospital. Branches also run along the side of Ensign Peak, and between East High School and University Hospital.

Damage and scarp formation is also occurring along two west valley faults, which geologists say tend to shake "in sympathy" when the larger Wasatch fault moves.

The Taylorsville Fault roughly follows I-215 northward from about 4700 South to Rose Park. The Granger Fault runs diagonally northwest from a point about 2700 West and 5400 South to about North Temple and 5600 West.

A scarp about 3 feet high forms along parts of those west valley faults (with the higher "mountain side" on the west instead of the east), as scientists earlier predicted.

That 3-foot scarp is not as high as the scarp along the main branches of the Wasatch fault, but the movement is enough to snap transportation and utility lines, divide communities and cause significant damage.

A huge area shakes

Damage is not limited to Salt Lake County. The entire Wasatch Front is now shaking from Brigham City on the north to Santaquin on the south, and from Tooele on the west to Coalville on the east.

It is affecting 80 percent of the population of Utah.

Shaking is so severe throughout Salt Lake County that virtually no one there is able to stand without falling. Unsecured hot-water heaters in many homes shake loose and break natural gas and water lines. Fires start.

Bookcases, furniture, pictures and other debris fall on people inside homes. Some who try to run outside are killed or injured by falling objects. (In contrast, the high and heavily loaded shelves in Lowes and Home Depot hardware stores do not fall because owners, working with the state, decided to anchor shelves for quakes.)

Collapsing buildings and walls are also killing and injuring people throughout the quake area — especially in older "unreinforced masonry" buildings made of bricks and mortar without reinforcing steel.

Next, the severe shaking makes some saturated, sandy soils act like a liquid, or more accurately like quicksand. This "liquefaction" causes some buildings to sink or roll over in unstable soils. Landslides follow in some areas.

Significant liquefaction occurs along the Jordan River. Most bridges across the river fail — as was predicted by state emergency officials in 2006 for such a quake. This essentially cuts the valley in half again, hampering emergency transportation and limiting how much each half will be able to help the other.