New Zealand quake’s impacts linger long afterwards; Construction on unstable soils amplified hazards

IN LIEU OF A LOO: For two long years now—since the devastating earthquake in September 2010—many residents of Christchurch, N.Z., have had to dispose of their waste in curbside bins for regular pick up because repairing sewer lines in unstable soils would be too costly. Photo by John D. Schelling, EMD

In August, John Schelling, Washington State Emergency Management Division’s earthquake program manager, visited Christchurch, New Zealand as part of a U.S. Geological Survey research project. Buildings and people in Christchurch experienced some of the strongest vertical motions ever recorded from the September 4, 2010, earthquake and its many aftershocks.

Schelling’s posting today on the Emergency Management Division’s blog describes the lessons we can–and should–learn about earthquake preparation and damage prevention. Large sections of the city crumbled because they were built on land susceptible to ground liquefaction. He notes that entire neighborhoods, even fairly new ones, in Christchurch have been abandoned because the instability of the land now makes it cost prohibitive to continue providing them with water, wastewater and electricity (see John’s photo with this article).

Mapping areas here in Washington that are susceptible to soil liquefaction and other hazards can help planners, builders and citizens better understand our potential risks from earthquakes. Geologists from DNR’s Geology and Earth Resources Division use modern geotechnical and geophysical methods, as well as historical records, to identify and assess geologic hazards. Most geologic mapping done by companies and universities is for a specific purpose and covers small areas. Our job as the state survey is to produce maps that cover whole areas of the state at various scales.

DNR’s geologists also hold workshops to show cities and counties how to use these maps for land-use and emergency-management planning. In response to the Growth Management Act’s mandate to use the ‘best available science’, our geologists meet with local governments and citizens in at-risk communities to educate them about geologic hazards and ensure that these hazards are considered in growth management and disaster planning.

DNR’s earthquake mapping and risk assessment are valuable tools here in Washington State where there is a 10 percent to 14 percent chance of a subduction zone earthquake and a 20 percent chance of a quake like the one that hit Christchurch in our lifetimes.

See DNR’s county maps of earthquake hazards.

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