Yeah the coast did drop but this is up the river several miles. There are beaches where sand erosion exposes tree stumps that were well above the water line at one time. The upper edge of the subduction zone sank when the earthquake released the tension on the upper side of the fault. The same thing happened at points in the Great Alaska Earthquake. Land settling is common but unpredictable at this point. If we could map and quantify the stress on different sections of the fault, it would help preparations greatly.