Rodgers Creek Fault

Rodgers Creek Fault
Name	Rodgers Creek Fault
Location	Northern California, United States
Type	Right-lateral strike-slip fault
Part of	San Andreas Fault system
Length km	~75
Displacement	~6–12 mm/yr (regional)
Notable events	1898–present seismicity studies

Rodgers Creek Fault is a right-lateral strike-slip fault in northern California that forms a major component of the San Andreas Fault system linking offshore structures with onshore faults near the San Pablo Bay and Santa Rosa region. It is a key element in regional seismic hazard assessments because of its potential to rupture in large earthquakes that could interact with the nearby Hayward Fault, with implications for infrastructure in San Francisco Bay Area, Marin County, California, Sonoma County, California, Contra Costa County, California, and San Pablo Bay Bridge corridors.

Geology and Structure

The Rodgers Creek Fault lies within the complex plate boundary between the Pacific Plate and the North American Plate, forming a strand of the broader San Andreas Fault transform system that includes the Hayward Fault, Calaveras Fault, Christmas Tree Pass Fault, and Green Valley Fault. Its mapped trace extends from near the southern end of San Pablo Bay across the coast‑range rocks of Sonoma Mountains into the Santa Rosa Plain and ties into offshore structures beneath the Gulf of the Farallones and Bodega Head region. Lithologies along the fault include deformed sediments of the Franciscan Complex, uplifted units of the Great Valley Sequence, and Quaternary alluvium deposited in basins like the Santa Rosa Plain and Petaluma River valley. Detailed mapping shows a primary strike-slip rupture zone with splays, stepovers, and a complex fault zone comprising strands, fault gouge, and breccia, similar in style to other strands such as the Maacama Fault and Healdsburg Fault.

Tectonic Setting and Fault Mechanics

The Rodgers Creek Fault accommodates right‑lateral shear between the Pacific Plate and the North American Plate with rates comparable to nearby structures including the Hayward Fault and San Andreas Fault (central section). Geodetic networks such as USGS campaigns, GPS arrays, and InSAR studies integrate data from institutions like UC Berkeley, Stanford University, and the California Geological Survey to constrain slip rates, locking depth, and interseismic strain accumulation. Mechanical models of rupture propagation examine stress transfer between the Rodgers Creek Fault and the Hayward Fault, invoking Coulomb stress changes studied in the context of events like the 1906 San Francisco earthquake and modeled scenarios for multi‑fault ruptures akin to the 2016 Kaikōura earthquake and 1857 Fort Tejon earthquake analogues. Fault zone properties (frictional strength, rate‑and‑state parameters) are inferred from borehole observations, seismic imaging, and analogs from experiments conducted at facilities linked to SCEC and IRIS.

Seismic History and Paleoseismology

Instrumental seismicity catalogs from USGS and regional networks document microseismicity beneath Santa Rosa and offshore beneath San Pablo Bay, with historical damage reports from 19th‑ and 20th‑century events used to infer past rupture behavior. Paleoseismic trenching investigations across Quaternary deposits in the Santa Rosa Plain and near Schellville and Petaluma have identified stratigraphic offsets, colluvial wedges, and radiocarbon‑dated horizons that constrain timing and recurrence intervals of large earthquakes, comparable to studies on the Hayward Fault and San Andreas Fault (southern). Results suggest multi‑thousand‑year paleo‑recurrence intervals with potential for co‑seismic rupture with adjacent faults, inspiring comparisons to segmented ruptures like those documented for the 2010 Maule earthquake sequence and historic sequences evaluated by Paleoseismology research groups.

Earthquake Hazard and Risk Assessment

Hazard models produced by entities such as the USGS National Seismic Hazard Model incorporate the Rodgers Creek Fault as a source capable of producing magnitude ~7.0–7.5 events, with scenario modeling examining simultaneous rupture with the Hayward Fault to produce larger, compound events. Urban and critical‑lifeline exposure analyses reference population centers including Santa Rosa, California, Novato, California, San Rafael, California, and the Richmond–San Rafael Bridge corridor, and infrastructure such as Interstate 80 (California), regional BART and Caltrain networks, oil terminals in Richmond, California, and the Petroleum and Gas terminals near San Pablo Bay. Risk mitigations draw on building codes developed by the California Building Standards Commission and retrofitting programs implemented by FEMA, municipal governments, and utility companies to reduce seismic risk to hospitals, schools, and ports modeled in HAZUS analyses.

Monitoring and Research

Continuous seismic and geodetic monitoring is provided by networks operated by USGS, CGS, UC Berkeley Seismological Laboratory, and cooperative arrays funded by agencies such as the National Science Foundation and programs like the SCEC Community Modeling Environment. Research priorities include dense seismic imaging across the fault with instruments from NCEDC, interferometric synthetic aperture radar (InSAR) campaigns from NASA and ESA missions, and paleoseismic trenching supported by universities and museums like the California Academy of Sciences. Collaborative modeling efforts use community codes and data portals developed by SCEC, while emergency planning exercises engage regional jurisdictions, Cal OES, and private stakeholders to test response to plausible Rodgers Creek–Hayward rupture scenarios.

Geomorphology and Surface Expressions

Surface geomorphic features associated with the fault include linear scarps, shutter ridges, sag ponds, offset drainages, and deflected stream channels observable in high‑resolution lidar produced by USGS and airborne missions from NOAA and state agencies. Landscape responses along the Rodgers Creek trace intersect protected areas like Annadel State Park and urbanized valleys around Santa Rosa where fault geomorphology is modified by anthropogenic activity linked to historical development patterns in Sonoma County, California and Marin County, California. Coastal expressions near San Pablo Bay and estuarine environments show submarine offsets and deformation analogous to offshore rupture signatures studied in the Gulf of Cádiz and Cascadia Subduction Zone contexts.

Category:Seismic faults of California Category:Geology of Sonoma County, California Category:Geology of Marin County, California