 To the south, the existence of a second fault, the Tacoma Fault, has buckled the intervening strata in the Seattle Uplift.Typical Puget Sound profiles of dense glacial till overlying permeable glacial outwash of gravels above an impermeable bed of silty clay may become unstable after periods of unusually wet weather and slump in landslides.The United States Geological Survey (USGS) defines Puget Sound as a bay with numerous channels and branches; more specifically, it is a fjord system of flooded glacial valleys.