BACKGROUND:

The Hayward Fault has shaped the landscape of the East Bay for the last million years.  The last large earthquake was on October 21, 1968, when a 6 foot offset was ripped from Milpitas to San Leandro.  In certain places there was an uplift of 4-6 feet.  Hayward, San Leandro, Oakland and San Francisco had major damage.  Fremont’s Mission San Jose crumpled. The Hayward Fault has created the scenic hills and valleys in the East Bay.  Much of the length of the Hayward Fault outlines the hills of the Diablo Range.  However in Fremont, the Hayward Fault's trace is through the flatland.

The Hayward fault, running through the East Bay from the North Bay to Santa Clara County, is one of a handful of faults in the world that ‘creeps’ at the surface. Fault creep, where a fault moves steadily at the surface (instead of staying locked by friction, like most faults), has many observable effects in the East Bay – it separates curbs and paving slabs, cracks asphalt and walls, and damages buildings, most notably the Berkeley football stadium. The rate of movement, around 5 mm per year in Fremont, is enough to visibly move objects within a year or two.

Geophysicists are interested in this unusual behavior for a couple of reasons. First, we want to explain why some faults creep and others do not – why it happens on the Hayward fault in Fremont, and not (for example) on the San Andreas fault in Palo Alto. Second, and more importantly, knowing where and how fast the Hayward fault creeps allows us to make estimates of where it is not creeping. These ‘locked’ areas are accumulating strain for a future earthquake. We know that there was a large earthquake on the Hayward fault in 1868, and our best estimates suggest that there is a high probability of a repeat earthquake in the next few decades. Understanding in advance where this earthquake will happen will allow citizens, the public utilities and city governments to prepare for the worst.