Where does the fault lie?

Without any obvious context, the geologist briefing the CWC mentioned the West Tracy Fault and told the Commissioners, “You’ve probably never heard of this.” 

According to a June 2007 technical report assessing faults in the Northeastern Diablo Range, the West Tracy Thrust Fault is a blind fault – the kind with no current surface trace – that runs northwest to southeast for about 70 km (about 43 miles) parallel to the eastern flank of the northern Diablo Range between the Marsh Creek outlet (near Brentwood and Oakley) and south of the Hospital Creek drainage west of Modesto.

The geologist didn’t come right out and say this, but we will:  Everybody concerned about seismic threats to water project deliveries should be looking at the West Tracy Fault, since it passes close to the pumping plants at Tracy.  A peripheral canal or tunnel through or under the Delta wouldn’t protect water transfers if there were a catastrophic seismic event on this fault or any of the other blind thrust faults running down the valley.

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