Malibu Coast Fault May Pose Threats

• Texas-Based Professor and Students Monitor Movement

BY BILL KOENEKER

A Texas-based geology professor argues throughout his various published papers, including the latest paper delivered during a recent geology symposium, that the Malibu coast fault may not be as benign as the current thinking goes about the earthquake fault zone that underlies much of Malibu and the Santa Monica Mountains.

“The geomorphology of the MCFZ is consistent with the interpretation that the MCFZ is active. Given the other indicators of fault activity, the trench studies that must still be undertaken across the MCFZ are more likely to establish the chronology of recent displacement along the MCFZ than to indicate that the fault is not active,” wrote Vincent Cronin.

Cronin teaches at Baylor University and oversees several graduate students who are currently working on projects dealing with earthquakes and faulting in the Malibu hills that are related to his research.

“Three current MS students are working on my research involving the recognition of seismogenic or potentially active faults in the central and western Santa Monica Mountains and northern Santa Monica Bay,” Cronin writes on his website.

At the presentation at the Geological Society of America Annual Conference in Philadelphia, Cronin and his colleague Lauren Seidman asserted that the current published models of the Santa Monica Mountains, “associate active faulting with only a few left-oblique reverse faults located directly adjacent to the coastline or just offshore. Reported earthquake locations and focal mechanism solutions do not support this limited view of the extent of active faulting.”

The purpose of the current study presented at the conference, according to the pair, is to map probable active faults within the Civic Center area and after utilizing various techniques of analysis and field work find possible correlations between surface faulting and reported earthquakes.

“These preliminary results suggest the need to modify current models of active deformation in the western transverse ranges, which are relevant to total assessment of seismic risk in the greater Los Angeles basin,” the report concludes.

In some of Cronin’s earlier work, he delves into the problems encountered by the geologist delivering bad news in such a high-profile wealthy neighborhood.

Cronin says it has been suggested that the local fault zone has not yet been formally recognized as an active fault zone because of the expected loss of property value should the designation be applied.

“Geoscientists fear being held liable for loss of property value, even though their assessment of fault activity may be scientifically valid. What are the ethical responsibilities of geoscientists involved in seismic risk assessment along the fault zone? Are political or financial considerations valid criteria to use in assessing the activity of a fault? These are not abstract questions of geo-ethics, because the lives and properties of countless people are potentially at risk,” he noted.

Cronin says the dilemma involves the potential conflict between the need to protect the safety of the public and the need to protect the property and wealth of the public by not mistakenly zoning faults as active.

“The resolution of this dilemma must come through the evolution of public policy and professional practice concerning the assessment of fault zone hazards. The formal reintroduction of the category potentially active, to characterize faults whose most recent displacement is ambiguous but that are likely to be active, might provide a useful intermediate category between active and inactive faults,” he concluded.