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Facts >> High Risk of Liquefaction in Proposed Patterson Ranch Development

These photos show wetlands in Coyote Hills. The United States Army Corps of Engineers and the Environmental Protection Agency jointly define wetlands as: Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.

The map below shows parts of the Bay Area where soils are at risk of liquefying in a strong earthquake. A 4.2 magnitude earthquake on or near the Hayward Fault hit Oakland on July 20, 2007. A 4.2 magnitude quake shook Lafayette on March 2, 2007. Geologists have long said the Hayward Fault is primed for a major snap—magnitude 7 or higher—and that the chances of one happening within the next 30 years is high.

Liquefaction occurs when loose, waterlogged soil is shaken. It loses strength and behaves like a fluid, causing buildings to sink in much the same way your feet sink into soggy sand at the edge of the surf.

When this happens, the ground isn’t strong enough to support structures; pipelines snap, and buildings sink and tilt. The risk is highest on artificial fill and along creeks and rivers.

An ancient delta that underlies much of Fremont, made of silt deposited by Alameda Creek, is rated at high risk (see orange area of Fremont).

Sources: U.S. Geological Survey and California Geological Survey 2006; http://earthquake.usgs.gov/regional/nca/qmap/

As the map shows, Ardenwood/Forest Park is highly susceptible to liquefaction in a strong earthquake. 

  • Is it logical and reasonable to build 520 high-density 2-story housing units, as proposed in the Patterson Ranch development, in front of Coyote Hills Park? Fremont has plenty of developable land, closer to the center of the city, which is at lower risk. Also, much of Patterson Ranch is wrapped by Crandall Creek, where its water would seep under the ground of the proposed development (see photos: top, east of Ardenwood Blvd.; bottom, west of Ardenwood Blvd.). This land is part of a floodplain.

  • Strong afternoon winds from SF Bay (less than a mile away) could exacerbate fires if gas and water line break in an earthquake. Housing collapse is more likely given their construction on manmade fill (require more than 130,000 cubic yards of soils to raise above flood level) on top of liquefacation-prone soil.

  • Across from the proposed Patterson Ranch development, the 15.5-acre Tupelo lot is being built densely with 276 3-story condos/townhouses and houses (see photo above).

  • If added to the proposed 520 housing units, there would be 800 housing units built on land that is highly susceptible to liquefaction. Multiplying 800 units of apartments/condos/townhouses/houses by 4 (average number of residents per housing unit) results in an additional 3,200 Fremont residents, who would need City services in an emergency. This is on top of the current residents who live in the 5,000+ densely packed homes in Ardenwood and Forest Park.

  • Don’t you think it is the responsibility of the Fremont City Council and Planning Commission to ensure our safety rather than approve a high-density housing development that would jeopardize local citizens’ safety? 

  • Developers would like to diffuse the problem by saying they would do whatever they can to minimize the dangers. What technology is a match for the strong forces of nature?

In conclusion, given the issues of liquefaction, floodplain, and safety of residents in an area already with the highest density in Fremont, should the Fremont city council have approved this proposed 520-housing unit Patterson Ranch development? (Note: Fremont experienced a 5.7 magnitude earthquake on October 30, 2007)

Click on the link below to see a simulation of 7.5 magnitude earthquake.

Trailer simulates earthquake (Then click on the small square on lower right to start video.)

 

 

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