Engineers: Metro Quake Fault Studies Incomplete

Engineering consultants told the Beverly Hills City Council Tuesday that a study of earthquake faults commissioned recently by Metro was incomplete and therefore inadequate to enable an informed decision on the Beverly Hills portion of the Westside Subway Extension.

Geotechnical firm Shannon & Wilson, Inc. was hired by the city at a cost of $100,000 to conduct a peer review of the Metropolitan Transportation Authority’s fault and tunnel reports. Metro staff recommended March 19 that the subway extension be routed under to Constellation Boulevard in Century City.

Shannon & Wilson suggested that the MTA order more thorough testing to determine the presence of active earthquake faults along the two proposed routes that go through Beverly Hills. Its report notes a disparity between the level of data gathered from the Santa Monica Boulevard route and the Constellation Boulevard route.

"When compared with the studies completed at the Santa Monica Station, the relatively sparse exploration data presented for the Constellation Station does not indicate, nor fully negate, the presence of faulting," the Shannon & Wilson report states. "We recommend that comparable geological and geotechnical explorations be carried out for the Constellation Station."

A key issue was the method of determining whether or not a fault is active.

"Trenching" is a more accurate though more costly way to investigate a fault zone, according to Shannon & Wilson. To date, Metro's scientists have only employed the "boring" method, which gathers a less comprehensive data set, the firm said.

Regarding tunneling below BHHS, the report indicates that tunneling probably would not impact existing campus facilities.

"The proposed BHHS underground parking garage could be constructed above the tunnel to a maximum depth of about 30 to 50 feet below grade, leaving at least 20 feet of undisturbed soil above the tunnels," the report states. "Risks associated with ground loss during construction, vibrations during construction operation, and hazards from methane and other gasses should be mitigated by the design plans and specifications for the project."

Shannon & Wilson also suggests relocating the proposed Santa Monica Boulevard station at least one block further east from its current proposed spot, which extends past Century Park East into the Santa Monica fault zone.

The 25-page report and 40 pages of related information can be found here.

Be sure to follow Beverly Hills Patch on Twitter and "Like" us on Facebook.