Re: Hopefully no one living downstream
Actually there's a lot of dams in tectonically active parts of the world. If the dam is well designed and constructed, and the geology appropriate they are amongst the most enduring assets ever created by man.
On the other hand, if the geology is inappropriate, it can be very difficult. A little story bears this out, along with the folly of building dams where they are convenient for people rather than where they are appropriate. Back in the 1970s, the publicly run Severn Trent Water Authority believed it needed additional reservoir capacity. After much umming and ahhing, central government granted the funds to build it, and also mandated that it should be built at Carsington in Derbyshire, largely on the grounds that they thought there was a dearth of recreational water sports facilities in the East Midlands, and with a side order of not needing to relocate too many of the natives. Carsington was a dry valley, with no significant water source, so this decision made it an expensive to build, expensive to operate pumped storage scheme, using 10km of tunnels and pumps to extract water from the River Derwent. It suited government because it was lightly inhabited, not exceptionally scenic, although the underlying geology was very poor. A Leicester based engineering consultancy went public when the work started, and predicted in one of the civil engineering publications of the day that the dam would fail, complete with diagrams showing the mode of failure. The water authority pooh-poohed this, and ploughed ahead. Some years later and few weeks before the topping out of the dam, it collapsed in exactly the manner that the Leicester based firm had foretold. £35m had been wasted building a castle in the sand, and it all had to be scraped away, redesigned and built properly, for an outturn price of around £105m, being completed years later, after privatisation of the water authority.
Had the dam lasted a bit longer, it would have been pumped full. And when it then collapsed, 35 million tonnes of water plus a few million tonnes of mud would have washed away the town of Ashbourne and most of its 9,000 inhabitants, before wiping out the 1,000 or so living in the village of Rocester, and causing untold damage further down on the River Trent in what would probably have been the world's second worst peace time dam failure.
All of this is a matter of public record if you know where to look, but is rarely presented in this way because the bureaucrats responsible didn't want to be embarrassed. I was involved a few years after the collapse, but as far as I know nobody was sacked (although the bitter and resentful engineers of the water authority made sure they never employed the consultants who'd predicted the outcome so accurately). The key takeaway is only ever build where the geology is ideal, and not to have your decisions swayed by the specifics relating to the peasants, be that the need to relocate them, or the desire to let a tiny fraction of them enjoy a bit of sailing.