13 January 2010
The Haiti earthquake – likely shaking damage to structures
Posted by Dave Petley
Over the last few years a number of studies have examined the level of damage associated with the intensity of shaking in earthquakes. The table below shows the relationship between shaking intensity (MMI) across the top and different types of building down the side. The number is the percentage of buildings damaged or collapsed:
Click on the table for a better view in a new window.
This is then helpful for examining the likely level of damage in Haiti, which can be estimated from the USGS shake map:
This should then be compared with the USGS data on the exposed population (MMI=7 and above only):
The USGS suggest that 137,000 people live in the MMI=X zone and a further 710 in the MMI=IX zone. Note that almost all of the news at the moment is from Port-au-Prince, which is in the MMI=VIII zone.
This GoogleEarth image shows some of the urban slums on the edge of Carrefour, in the MMI=IX zone, before the earthquake. As most of the buildings here are likely to be unreinforced masonry, the building collapse rate is probably 80% or more. This could be higher due to the effects of the slopes, which both increase the intensity of shaking and make the foundations less secure.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Meanwhile, there is post-earthquake imagery available in GoogleEarth. The network link is: http://mw1.google.com/mw-earth-vectordb/haiti/Haiti-Earthquake-nl.kmlThe latest pre-EQ imagery is from Feb. 2009.It is really, really sad to see the devastated city and still hard to imagine how people must suffer in this area. For landslides, the area south of Carrefour maybe is of interest. Some mass movements visible there might be due to the earthquake. Hard to say, since the timespan between the two photos is almost a year.