Earthquakes near Anchorage

211 earthquakes of M4.0 or larger were recorded within 200 km in the last 10 years — one of the most active rates. Many of them are aftershocks of the November 30, 2018 M7.1 Anchorage earthquake, so the count overstates the lone-event rate. Since 1900 the catalog holds 1030 M4-or-larger events within the same radius.

Anchorage knows this ground as well as any American city: the M9.2 of March 27, 1964 — still the largest earthquake ever recorded in North America — devastated downtown, and the M7.1 of November 30, 2018, centered almost under the city at Point MacKenzie, damaged roads, schools, and thousands of homes.

Southcentral Alaska sits above the place where the Pacific Plate slides beneath North America — the Aleutian megathrust. That collision built the Alaska Range and produced the two largest earthquakes in recorded U.S. history. Most of the region's shaking comes in three flavors: megathrust earthquakes offshore in the Gulf of Alaska and Prince William Sound, earthquakes inside the sinking Pacific slab 30 to 150 km down (the kind felt as a long roll across the whole region), and shallow breaks on crustal faults like the Castle Mountain fault in the Matanuska Valley.

New to the numbers? What magnitude means explains the scale in plain words — including why a whole step is about 32 times the energy, and why what people feel is not the same as damage.