CPENG78 - First, for a very large part of the Haitian population, maybe even a majority, I think the choice is not between poorly constructed housing and proper construction, but between poorly constructed housing and NO housing. To people who literally eat patties of soil for the small amount of nutrients in them, steel is quite expensive. Doesn't matter what the building codes say if you can't afford to follow them. It may be a perfectly rational decision to live in an adobe house with say, 1 percent chance of collapse due to earthquake each year, rather than living in no house at all or a hovel built from sticks and tarps.
Second, it is fairly common to see areas of severe damage interspersed with areas of little damage, like you describe. Structures on rock or on thin soil above rock tend to be loaded by lower peak acceleration, generally shorter-period motion, and fewer strong cycles compared to those on alluvial or other soils, because of the dynamic response. It was seen in the Loma Prieta, where areas of fill along the waterfront experienced much worse shaking than areas on rock much closer to the epicenter. In the 1925(?) Santa Barbara EQ, downtown Santa Barbara CA, on thick alluvium, was severely damaged, whereas higher ground a short way north, on bedrock or a thin layer of soil above bedrock, experienced much less damage. Think of Jello in an iron pan. One reason the Mexico City earthquake was so destructive, even though the epicenter was very far from Mexico City, was the thick lacustrine sediments.
rmw - I too would go back to DR in a heartbeat. Great people, great coffee, great merengue music by Cuatro Cuarenta. Haven't been to Haiti.
Regards,
DRG
