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Secondary Earthquake Hazards

2018-01-03  |   Editor : houguangbing  

"Earthquakes is one of the predominant natural hazards in the world, with approximately 150 major events (Mw > 6.0) occurring per year. More than 460,000 people have died due to the direct effects of earthquakes since 2000, including seismic shaking and tsunami.

Earthquakes also trigger a variety of phenomena that may represent significant hazards, in terms of damage to infrastructure, direct economic cost and lost productivity. These include landsliding, deforestation and loss of vegetation, disruption of groundwater and surface water flows and catastrophic river bed aggradation caused by increased sediment flux. While the direct effects of earthquakes are established and often spectacular, the activity of these secondary phenomena and their long-term economic and societal costs are commonly overlooked. But it is plausible that their associated costs may approach, or even surpass, the effects of the earthquake itself.

Secondary phenomena may be important for two reasons

Phenomena like river bed aggradation and increased sediment supply are likely to be temporally persistent for much longer than the duration of the main event. This makes them both politically and operationally difficult to address. While an earthquake may impact upon large areas, the secondary effects are likely to be spatially heterogeneous. Combined with disruption to key infrastructure such as transport links in the main event, complicated efforts for response and mitigation. A key issue in allocation of post-event resources is to understand the distribution of secondary hazards in space.

Coping with Secondary Hazards

Acute disaster response mechanisms may not be well-suited to addressing secondary hazards and indeed may themselves be compromised as these hazards evolve (for example, if displaced residents are moved to temporary housing that is later put at risk of flooding or aggradation). Emphasis on short-term relief means that infrastructure must be restored and resources allocated very rapidly after an event, before the extent and severity of secondary phenomena can be sufficiently established. Likewise, short timescale relief funding (generally awarded for periods of less than 3 years; World Bank IEG, 2006) is unlikely to be able to provide the extended support needed to assess and respond to secondary phenomena in a sensible manner.

The upshot is likely to be that scarce redevelopment resources are wasted through application to areas which are then threatened, or at worst overrun, by secondary phenomena. All of these issues point to serious gaps in our understanding of post-seismic landscape response, development and recovery. We simply do not understand the duration of secondary phenomena such as landsliding and sediment aggradation, nor do we have the tools to rapidly assess their severity after a given earthquake. Thus, we cannot compare the impacts of post-seismic processes with those of the earthquake and we risk overlooking less obvious, but perhaps no less important, long-term effects. The development of key predictive tools and the efficient exchange of this information between relief agencies, economists and local governments, could lead to more efficient allocation of disaster relief resources in space and time. It could also assist in restoring resilience and independence to affected communities, by ensuring that efforts to rebuild infrastructure and economic capacity are not frustrated by secondary hazards."


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