Surface fault rupture

▲ 15.2 A suburb is planned so that an active fault (white dashed line) passes through a green strip. Upper Hutt, New Zealand.

(Lloyd Homer, Institute of Geological & Nuclear Sciences, Ltd, New Zealand).

▲ 15.2 A suburb is planned so that an active fault (white dashed line) passes through a green strip. Upper Hutt, New Zealand.

(Lloyd Homer, Institute of Geological & Nuclear Sciences, Ltd, New Zealand).

One of the most obvious steps that planners take to reduce the seismic vulnerability of a community is to limit construction over known active fault lines. Any building subject to fault movement beneath its foundations can expect severe damage depending upon the magnitude of fault displacement. Movement along a fault line may be confined to the horizontal plane inducing a shearing-action into the foundations of a building above it. Yet perhaps significant vertical movement results in part of a building attempting to cantilever over the lowered ground. The distortions induced in a building straddling a fault cause far more severe damage than that caused by ground shaking alone. Because buildings sited over a ruptured fault are highly likely to at least partially collapse, the increase in the number of casualties can be significant. Fortunately, in even the most fault-ridden cities, the percentage of affected sites is very small due to the narrowness of surface fault zones which are usually of the order of several tens of metres wide.

The Californian Alquist-Priolo Earthquake Fault Zoning Act of 1972 requires the State Geologist to ' delineate "Earthquake Fault Zones" among known active faults...'9 Local government agencies of affected areas require geological investigation of the hazard. Any building for human occupancy must be set back 15 m from an active fault. Single-family light-weight dwellings up to two storeys high are among several exemptions. While adopting a similar approach, recent New Zealand guidelines take the Californian requirements a step further by taking into account factors such as the accuracy with which a fault can be located, its average faulting recurrence interval and the importance of the proposed building to the community (Fig. 15.2).10

▲ 15.3 Devastation to the built environment by the 2004 Indian Ocean tsunami. Banda Aceh, Indonesia. (Reproduced with permission from Regan Potangoroa).

▲ 15.4 An inundation map for a section of the US West Coast for a tsunami caused by a magnitude 8.8 undersea earthquake.

(Adapted from a map, State of Oregon, Dept. of Geology and Mineral Industries).

▲ 15.4 An inundation map for a section of the US West Coast for a tsunami caused by a magnitude 8.8 undersea earthquake.

(Adapted from a map, State of Oregon, Dept. of Geology and Mineral Industries).

The need for such guidelines to reduce hazards from surface faulting has been dramatically emphasized by the July 2007 earthquake damage to the Kashiwazaki nuclear power plant in Japan. Apparently the plant is built directly above an active fault line: 'The long, straight ridge and crevice that now runs alarmingly through the middle of the plant, said one of Japan's most respected seismologists, proves that' ' 11

Was this article helpful?

0 0
Greener Homes for You

Greener Homes for You

Get All The Support And Guidance You Need To Be A Success At Living Green. This Book Is One Of The Most Valuable Resources In The World When It Comes To Great Tips on Buying, Designing and Building an Eco-friendly Home.

Get My Free Ebook


Post a comment