Dynamic models of an earthquake and tsunami offshore Ventura, California

Abstract

The Ventura basin in Southern California includes coastal dip‐slip faults that can likely produce earthquakes of magnitude 7 or greater and significant local tsunamis. We construct a 3‐D dynamic rupture model of an earthquake on the Pitas Point and Lower Red Mountain faults to model low‐frequency ground motion and the resulting tsunami, with a goal of elucidating the seismic and tsunami hazard in this area. Our model results in an average stress drop of 6 MPa, an average fault slip of 7.4 m, and a moment magnitude of 7.7, consistent with regional paleoseismic data. Our corresponding tsunami model uses final seafloor displacement from the rupture model as initial conditions to compute local propagation and inundation, resulting in large peak tsunami amplitudes northward and eastward due to site and path effects. Modeled inundation in the Ventura area is significantly greater than that indicated by state of California's current reference inundation line.

Shelf evolution along a transpressive transform margin, Santa Barbara Channel, California

“…Models in Greene et al (2006) suggest that tsunamis generated by the Holocene Goleta slide (Figs. 2 and 21A) could have achieved local runups of 10 m. Ryan et al (2015) developed a tsunami model for an M w 7.7 earthquake on the Pitas Point fault, characterized by a 40-km-long rupture and more than 7 m of abrupt seafloor relief, generating a local tsunami height of 7-8 m. This model locates the Pitas Point fault ~2-3 km north of the fault tip that we map (Fig. 2), and also incorrectly inputs the Pitas Point fault as a seafloor-rupturing structure, not a blind fault that progressively deepens to the west.…”

Mechanical models favor a ramp geometry for the Ventura‐pitas point fault, California

“…Evidence for several large magnitude (~M8) multi‐fault ruptures has recently been suggested to have occurred along the Ventura‐Pitas Point fault system in southern California [ Hubbard et al, ; McAuliffe et al, ; Rockwell et al, ]. The potential effects of a repeat event of this type on the densely populated urban areas of the Ventura and Los Angeles basins are likely severe, including strong shaking [ Field , ], tsunami formation and associated infrastructure damage and human and economic losses [ Ryan et al, ]. Therefore, detailed knowledge of the subsurface fault geometry of this system is vital for accurate future hazard assessments in southern California.…”

The California Seafloor and Coastal Mapping Program – Providing science and geospatial data for California's State Waters

“…Local models in the Santa Barbara Channel 288 suggest tsunami run-ups from 8,000 to 10,000 ybp submarine landslides(Fisher et al, 2004) in 289 the Goleta complex (130 km 2 ,Fig. 5a) could have reached 10 to 15 m(Greene et al, 2006; 290 Borrero et al, 2002), and at least 8 m of runup has been modeled for offsets on the Ventura-Pitas 291Point fault(Ryan et al, 2015). Smaller submarine landslides are also present on the continental 292 slope west of the Goleta slide (e.g., the Gaviota slide, parts of the Conception fan;Fig.…”