Echelon Cracks at Lake Temescal
The Hayward Fault in Oakland, California
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This set of echelon cracks at Lake Temescal Regional Recreation Area runs straight to an interpretive sign pointing out their significance. Fault traces are rarely this obvious. Moreover, this trace is only one element of a wider complex of cracks and slivers tens to hundreds of meters wide that makes up the fault zone. Indeed, the Hayward fault is only one element of a complex plate boundary that includes the San Andreas fault and several other major faults.
Under this spot, the U.S. Geological Survey has emplaced a creepmeter across the fault trace. That is a wire strung between two concrete piers in an underground vault isolated from the surface environment. Its data is fed to a satellite link and onto the Web.
Photo (c) 2005 Fleur Helsingor, reproduced by permission. (fair use policy)
