How can geology be used to minimize risk?

Geology and earthquake impact

The damage resulting from an earthquake is influenced by three important geologic processes:

bulletAmplification: The type and depth of soil at a site affects the severity of ground shaking. In most cases, shaking on soil is greater than shaking on rock. In some situations a resonance can occur in deep soil layers, markedly amplifying the shaking at certain frequencies. If the frequencies are potentially damaging to a structure, the results can be disastrous.
bulletLiquefaction: Shaking caused by an earthquake can cause the transformation of some loosely packed, water-saturated sediments, such as sand and mud, into a fluid mass. The sediments thus lose their strength and can no longer support buildings which may then sink or lean. Soils which are most likely to liquefy are recently deposited sediments that can be found in certain parts of deltas, river channels and uncompacted landfills.
bulletLandslides: These are one of the major causes of damage resulting from an earthquake, and occur most often in areas of unstable loose sediments, such as steep mountainous slopes.

 

Cracked chimney, Courtney 1946
Damage to chimney on building in Courtney resulting from the 1946 earthquake (photo courtesy of the Geological Survey of Canada).

Although no area will be totally safe during an earthquake, in general, zones containing loose, wet sediments will suffer the most severe effects. Areas with bedrock near the surface tend to be more stable.

Understanding geology can help predict where earthquake damage will be greatest.

Minimizing the risk

Earthquakes can cost billions of dollars and thousands of lives. While we cannot prevent earthquakes, we can reduce the physical effects of such events by using our knowledge of geology to identify and avoid or modify sites where an earthquake can be expected to have the greatest severity. Detailed geological and geotechnical study of the properties and depth of surface sediments can be used to predict amplification of earthquake waves. Geological mapping of areas where landslides and ground liquefaction may occur, can aid in urban planning and in the development of emergency procedures for earthquakes. Ongoing monitoring of seismic activity in the province by geophysicists is essential to further our understanding of earthquake hazards in the province.

 

Lower Mainland seismogeological zones
The map of Greater Vancouver Illustrates three simplified geological zones that are incorporated into the National Building Code of Canada for use in the design of large structures. Green: compact or stigg soils <15m thick and bedrock. Yellow: compact or stiff soils >15m thick; and loose or soft soils <15m thick. Red: Loose or soft soils > 15m thick. (Adapted from Ministry of Environment report, 1979).

Earthquakes are an unavoidable natural hazard, but their destructive power can be reduced by geologic studies, proper planning and a well informed public.

Earthquakes in B.C. Home Page

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Earthquakes in British Columbia was originally produced as Information Circular 1991-6 by the BC Geological Survey of the B.C. Ministry of Energy, Mines and Petroleum Resources, in cooperation with the B.C. Ministry of Environment, the B.C. Provincial Emergency Program and with the assistance of the Geological Survey of Canada. It has been amended and updated in this WWW version.

Copies are available from:

Publications Office
BC Geological Survey
Ministry of Energy, Mines and Petroleum Resources
P.O. Box 9333. Stn Prov Gov't
Victoria, B.C.
V8W 9N3

 

  This page was last updated Wednesday, March 08, 2006