Significant Earthquakes and Faults
Fault Name Index
Cucamonga Fault Zone
Type of Fault: thrust
Length: about 30 km
Nearby Communities: Claremont, Upland, Cucamonga
Slip Rate: between 5 and 14 mm/yr
Interval Between Major Ruptures: estimated at roughly 600-700 years
Probable Magnitudes: MW6.0 - 7.0
Most Recent Rupture: very recent Holocene
Other Notes: Typical ground rupture per major event estimated at 2 meters. Slip rate (and thus recurrance interval) is somewhat disputed. If fastest slip rate is assumed, surface rupture interval may be as short as 150-200 years. This zone of faulting dips to the north.
The Cucamonga fault zone is part of the same fault system, marking the southern boundary of the San Gabriel Mountains, as the Sierra Madre fault zone. Sometimes it is included as part of the Sierra Madre fault zone, as is the San Fernando fault zone far to the west; here we refer to each as separate fault zones, as it is not clear that rupture may progress from one to another. Perhaps the best way to rectify the difference in nomenclature is to refer to the Cucamonga fault zone, Sierra Madre fault zone, and the San Fernando fault zone as the Sierra Madre fault system.