Geology of Seattle & The Puget Sound

[Webster]

The hills and lakes of Seattle, Washington are a direct result of multiple Puget Lobe advances during the Ice Age. Beneath the drumlins, outwash, glacial troughs, and scattered glacial erratics lies the Seattle Fault, an active fault which has produced numerous magnitude 6 or higher earthquakes since the Ice Age.

Interstate 90 exposes much of this geology in its first few miles heading east from downtown. The freeway begins on old tidelands that were filled by early residents of Seattle. Hills composed of soft glacial deposits were moved and dumped into Elliot Bay to make new land for a growing city. Today’s SODO district - including stadiums for the Seattle Seahawks and Seattle Mariners - sits on filled tidelands that are especially prone to seismic shaking during the next big earthquake in the Puget Sound.