If the ground shakes along Ventura, the fault line could generate a nearby tsunami, causing the waters to reach the shorelines in more or less just 30 minutes.
A team of researchers from the University of California Riverside (UCR) and the US Geological Survey showed the vulnerability of the Ventura and Oxnard areas through a simulated earthquake and the tsunami that could arise from it.
The researchers made use of two different modeling codes - one was for the earthquake and the other, for the tsunami. The study was published in the online journal Geophysical Research Letters Aug. 18.
The 3D model demonstrated a vertical seafloor deformation due to the earthquake, which was in turn used as an input to the tsunami model to bring to life a tsunami. The tsunami code then calculated the propagation, as well as inundation of tsunami.
According to David D. Oglesby, PhD, a geophysics professor at UCR and a co-author of the study, their research differs from others in that they used a simulated dynamic earthquake in calculating the displacement of the seafloor.
"Dynamic models such as these calculate movement in time by looking at the forces on and around the fault in time," the geophysics professor added, explaining that they are physics-based, being calculated results of models that demonstrate fault slip distribution and ground motion.
Specifically, a 7.7 magnitude earthquake along the Pitas Point and Red Mountain faults lead to large tsunami amplitudes that make their way northward and eastward of the fault, because of the coastline and the seafloor's shape.
The model demonstrated the earthquake occurring more rapidly than the tsunami. In the first 20 seconds of the model, the fault slips, and seismic waves move away toward all directions. With the seafloor vertically displaced, the tsunami is generated and begins to propagate through the ocean outward.
As the tsunami moves north, it eventually reaches Santa Barbara as it arrives at the northward coastline in just five minutes. Towards the south, part of the tsunami moves to the deeper water along the Santa Barbara Channel.
The deeper water, along with the local bathymetry, causes the tsunami to retract in after about five to ten minues. The tsunami then rotates counterclockwise, propagating in the direction of and reaching Ventura and Oxnard in 15 to 20 minutes. As it arrives there, it inundates the area in no more than 30 minutes.
The researchers did not actually predict an earthquake and tsunami to soon hit Ventura or Oxnard.
"This is a single simulation of a single scenario - earthquake and tsunami - in the region, so it really shouldn't be used to define seismic hazard or emergency responses in its current state," said Oglesby. "This is an ongoing effort to establish a better tsunami hazard calculation for the area."
