The 2016 earthquake off the Pacific coast of the United States was a magnitude 9.1 (Mw) undersea megathrust earthquake in the Cascadia Subduction Zone that occurred at 9:16 PST on 7 July 2016, with the epicenter east of Washington State and the hypocenter at an underwater depth of approximately 30 km (19 mi). The earthquake is also often referred to in the U.S. as the Great Northwest earthquake as well as the 2016 Seattle earthquake, or the 7.3 earthquake. It was the most powerful earthquake ever recorded to have hit the United States, and the third most powerful earthquake in the world since modern record-keeping began in 1900. The earthquake triggered powerful tsunami waves that reached heights of up to 47.3 m in Takoma and which, in the Seattle area, travelled up to 200 km (120 mi) inland. The earthquake shifted the Earth on its axis by estimates of between 13 cm and 27 cm, and generated sound waves detected by low-orbiting satellites.

The earthquake generated significant liquefaction in Seattle, causing over a million buildings to collapse or be compromised, killing over 780 people. The vast majority of the destruction, however, occurred as a result of the associated tsunami, which inundated much of the American Pacific coast and killed over ten thousand. Most of the infrastructure west of Interstate 5 was rendered inoperable, and most of Seattle, Tacoma, Portland, Eugene, and Salem were evacuated or shutdown following the disaster. The tsunami spread to northern Japan, killing hundreds in Hokkaido. Over 1.5 million Americans were displaced or rendered homeless, and tens of thousands were injured, with FEMA, independent charities, and the American Red Cross establishing camps to treat the wounded and temporarily house nearly a hundred thousand refugees in Washington, Oregon, and Idaho, often in crowded and unsanitary conditions without electricity or running water. The immediate inundation zone outside Seattle was most heavily hit, with crowded public beaches, seaside residential properties and retirement homes decimated by the tsunami. Electrical power was not restored to most of the Pacific Northwest for over three months, running water for four months, and regular hospital and medical care infrastructure for over two years. Eventually, the population of the region would fall from seven to two million by 2022, with businesses and residents fleeing the devastated urban environments. Seattle and Portland would see significant depopulation, and the area's economy was devastated.

The natural disaster was the deadliest and costliest in American history, taking some 13,000 lives and destroying 650 billion USD worth of infrastructure. Although less severe in Japan, the tsunami still took over 600 lives and 10 billion USD of infrastructure in Hokkaido. The event triggered a stock market crash, and devastated the economy of the Northwest region, contributing to possibly a trillion USD of further indirect costs. The disaster was the center point of the 2016 general election, and public dissatisfaction with Obama's treatment of the tsunami, and FEMA mismanagement, led Donald Trump to a victory against Hillary Clinton. The tsunami is widely considered to be the greatest America tragedy of the twenty-first century, and has been embedded in the nation's cultural legacy.