By Michael Picarella pic@theacorn.com

Moorpark lies in a region with several active faults and is subject to the risks and hazards associated with earthquakes.

According to city officials, the faults that have the greatest impact on the city of Moorpark are the San Andreas Fault Zone, the Simi-Santa Rosa Fault Zone, the Oak Ridge Fault, the San Cayetano Fault and the Santa Susana Fault.

"Any of these fault lines can be dangerous," said Moorpark City Engineer Brad Miller.

San Andreas Fault Zone

The San Andreas Fault is the principal boundary between the Pacific and North American Plates and is made up of five segments. The Carrizo and Mojave segments, which extend from Central California to San Bernardino, are the closest to the Moorpark area, where they join near the Tejon Pass about 35 miles away. The two segments are estimated to be capable of producing magnitude 7.2 and 7.1 earthquakes, respectively.

Simi-Santa Rosa Fault Zone

The Simi-Santa Rosa Fault Zone consists of a series of closely spaced faults that extend in an east-northeast direction across the central part of Ventura County for a distance of more than 25 miles. In the Moorpark area, many small faults have been mapped within the fault zone, as well as several fault splays that branch off the main faults to the northeast.

Seismic activity along the Simi-Santa Rosa Fault Zone appears to be relatively low, according to sources, but such data is very limited.

In the southern part of Moorpark, the California Division of Mines and Geology has designated an Alquist-Priolo Fault Zone for many of the traces of the Simi-Santa Rosa Fault Zone, according to the city of Moorpark.

The Alquist-Priolo Fault Zoning Act was passed in 1972 and was a direct result of the 1971 San Fernando Earthquake, which was associated with extensive surface fault ruptures that damaged numerous homes, commercial buildings and other structures.

The Alquist-Priolo Fault Zoning Act’s main purpose is to prevent the construction of buildings used for human occupancy on the surface trace of active faults, according to sources. The act only addresses the hazard of surface fault rupture and isn’t directed toward other earthquake hazards.

Oak Ridge Fault

The Oak Ridge Fault extends westward from the Santa Susana Mountains, along the southern margin of the Santa Clara Valley, across the Oxnard Plain, and into the Santa Barbara Channel. Like the San Andreas Fault, the Oak Ridge Fault has been divided into segments, the closest of which is about three miles away from the northern part of Moorpark.

Although the fault is considered to be a significant seismic source, most of it hasn’t been assigned to an Alquist-Priolo Earthquake Fault Zone, Moorpark officials said. According to sources, the magnitude 6.7 Northridge Earthquake of Jan. 17, 1994 is believed to have occurred on the eastern extension of the Oak Ridge Fault in the Santa Clarita area. Minor land sliding and ridge-top shattering was observed in the hills above Moorpark as a result of this earthquake.

San Cayetano Fault

The San Cayetano Fault is one of the two deeply rooted and north dipping thrust faults that form the northern boundary of the Ventura basin. At its closest point, this fault is about five miles from the city. Several small earthquakes have been associated with this active fault.

Santa Susana Fault

The Santa Susana Fault merges with the Oak Ridge Fault in the west and the San Fernando Fault zone in the east. The fault is located about four miles east-northeast of the Moorpark area. This fault is estimated to be capable of generating a magnitude 6.6 earthquake, Moorpark officials said.

If there were potential hazards in Moorpark, especially where housing and commercial developments have sprung up, they would’ve been taken into consideration during the development, according to Miller.

"Mitigations usually would consist of building restricted areas," Miller said. "If there’s a fault hazard zone established or identified, it’s restricted. You can’t build anything there."