I need a report on a historical geotechnical failer that happened on February 9, 1971, had a massive earthquake in the foothills of the San Gabriel Mountains in southern California, causing severe damage to the lower Van Norman Dam. so please focus on the lower van norman dam failure.
1) what happened?
2) why did it happen? that is, what were the technical causes of the failure?
3) were there other contributing factors such as managerial decisions or operator error?
4) what were the costs of the failure in lives and economic damage?
5) what changes were made because of the failure?
6) what lessons can we draw from the failure?

use resources from the internet but don’t just copy-paste and please put the references