California Geological Survey issues new tsunami hazard maps for these Bay Area counties

Earthquake swarm: Drivers dodge boulders in the Sierra

Drivers dodged boulders in the eastern Sierra when a 6.0 magnitude earthquake struck near the California-Nevada border Thursday and then a swarm of aftershocks followed. Rockslides were triggered in Mono County briefly closing miles of U.S. 395.

SACRAMENTO, Calif. - The California Geological Survey (CGS) released new tsunami hazard maps for San Francisco, Contra Costa, and Santa Clara counties, useful for determining where to evacuate when a major Tsunami hits.

The new interactive maps released on Thursday were to replace the maps published in 2009. It included "buffer" zones in the inland areas, accounting for the potential miscalculations during modeling. Moreover, the CGS team also took reference to the "hard lessons" Japan learned during the Tohoku-oki Earthquake and Tsunami in 2011, according to the CGS press release.

"Japan utilized data from several hundred years of tsunami records in its planning, which seemed perfectly reasonable," said Dr. Steve Bohlen, the Acting State Geologist of California and head of CGS. "Then it was impacted by a once-a-millennium tsunami. So, we’re taking a very conservative approach and using a thousand-year scenario as the baseline for our new maps, hoping to avoid the tragic loss of life experienced in Japan.

The map was created with the worst-case scenario in mind, a magnitude 9.3 earthquake in the eastern Aleutian Islands.

Some of the major changes to the maps include increasing the hazard areas around the North Beach and downtown Market Street area in San Francisco county, and the residential and commercial areas around the port of Richmond in Contra Costa county.

The CGS has released Tsunami Hazard Area Maps for 13 coastal counties to date and plans to release the updated maps for the other 7 coastal counties next year, according to the press release.