City of Fremont

Clear evidence of creep is found in Fremont where the Hayward fault crosses Gardenia Way near Ivy. A diagonal sequence of fractures or shears, called en echelon shears, form in the asphalt of the street. These tears in the asphalt are due to the right-lateral movement of the fault. These shears are left-stepping, where the next or adjacent fracture is to the left of the last one. En echelon shears can be observed at many locations in the streets along the Hayward fault.


1992 - En echelon shears crossing Gardenia near Ivy in Fremont.

The Hayward fault can be identified at several locations crossing the streets in Fremont by the bending and breakage of curbs along the streets such as this one at Rocket Drive.


1993 -
Bent and broken curb at Rocket Drive.

SOUTH HAYWARD

On undeveloped hill slopes, the fault trace is marked by streams that are bent, almost at a right angle by the right-lateral movement of the fault. Right-lateral means that the land on the side across the fault moves to your right. In fact, the movement is primarily on the Bay side of the fault moving to the north. The stream in the photograph was originally straight. Thousands of years of fault slip in large earthquakes and slow fault creep have moved the stream eighty meters or about 260 feet northward relative to the opposite side of the fault.


Right-lateral stream offset.

In places, the Hayward fault can be observed as a line of green vegetation when the grass on the hills dries out in the spring. The line of vegetation marks the fault. It remains green because of seeps and springs formed along the fault. Seeps and springs form because the rock in the fault zone has been pulverized by fault movement and altered to clay. This pulverized rock and clay is called fault gouge. Gouge, part way up the hillside, forms an underground dam. Water moving down slope underground, accumulates against the fault gouge and comes to the surface as seeps, springs, and ponds.


The springs in the photograph are located uphill from the building
on the left and above the sign in the foreground.


Continuing northward , this old fence at
Holy Sepulchre Cemetery in south Hayward
has been offset by fault creep more than 3 feet
since it was built in the nineteenth century.


A small gully on the hillslope above has been Holy Sepulchre
Cemetery has been offset by fault movement nearly 3 meters
(about 6 feet) as illustrated by the red stakes. This offset
probably represents surface displacement in the 1868
Hayward earthquake and accumulated creep, plus possible
offset in an unknown fault rupture and earthquake before 1868.

Back to the Tour of the Hayward Fault

Copyright Dr. Sue Ellen Hirschfeld

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