Alaska earthquakes

M6.5 earthquake 57 km S of Adak, Alaska

A magnitude 6.5 earthquake struck 57 km S of Adak, Alaska on Tue, Jun 17, 1986, 11:05 PM HADT (08:05 UTC), 27 km (17 mi) below the surface.

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The earthquake

Magnitude: 6.5 (Mw, moment), strong
Magnitude from: USGS National Earthquake Information Center
Local time: Tue, Jun 17, 1986, 11:05 PM HADT
UTC: 1986-06-18 08:05:15 UTC
Depth: 27.0 km (16.8 mi), shallow
Epicenter: 51.356° N, 176.653° W
Region: Alaska
Strongest shaking: V, moderate shaking
Tsunami flag: No
Status: Reviewed by a seismologist

Magnitude estimates

Different scales measure different things and differ by a few tenths. The USGS marks one as preferred, and it is the one this page uses.

Mag.	Scale	Computed by	Notes
6.5	Mw, moment	USGS National Earthquake Information Center	Preferred · Reviewed
6.45	Mw, moment	ISC-GEM global catalog	Final · ±0.1
6.47	Mw, moment	USGS historic United States catalog	Final
6.4	Mwc, centroid moment	Global CMT project	Preliminary

What happened

The USGS’s account of the effects of this earthquake.

Felt (IV) on Adak and (III) on Atka. Depth 23.2 km. from broadband displacement seismograms. FAULT PLANE SOLUTION: P-Waves NP1:Strike=57 Dip=65 Slip=90 NP2:Strike=237 Dip=25 Slip=90 Principal Axes: (T) Plg=70 Azm=327 (P) Plg=20 Azm=147 Comment: The focal mechanism is poorly controlled and corresponds to reverse faulting. The preferred fault plane is NP2. CENTROID, MOMENT TENSOR (HRV) Data Used: GDSN L.P.B.: 20S, 48C M.W.: 8S, 19C Centroid Location: Origin Time 08:05:19.1 0.2 Lat 51.71N 0.01 Lon 176.54W 0.03 Dep 44.5 0.9 Half-duration 6.3 Moment Tensor; Scale 10**25 D-CM Mrr=4.56 0.07 Mtt=-3.92 0.06 Mff=-0.64 0.05 Mrt=2.60 0.12 Mrf=2.54 0.12 Mtf=-1.53 0.05 Principal Axes: (T) Val=5.96 Plg=68 Azm=302 (N) Val=-0.30 Plg=11 Azm=60 (P) Val=-5.66 Plg=19 Azm=154 Best Double Couple:Mo=5.8*10**25 NP1:Strike=261 Dip=28 Slip=113 NP2:Strike=55 Dip=64 Slip=78

Maximum observed Modified Mercalli Intensity (MMI) IV

From the USGS event page for usp0002v5r. U.S. Geological Survey text and figures are in the public domain.

Shaking

The USGS ShakeMap: shaking estimated from seismic stations and the quake’s size, on the Modified Mercalli intensity scale.

Strongest estimated: V, moderate shaking
Map: Automatic

USGS ShakeMap: estimated shaking intensity around the epicenter — Estimated shaking intensity. Map: USGS ShakeMap.

Did you feel it?

No one has reported feeling this quake to the USGS.

Nearby

Within 100 km, magnitude 3.5 and up: 40 in the 60 days after this one and 25 in the 30 days before it.

After

Before

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Sources

From the USGS Earthquake Hazards Program and its partner networks, event usp0002v5r (also filed as gcmtc061886a, ushis3955, gcmt19860618080516, atlas19860618080516, iscgem493430). Read Thu, Oct 1, 2026, 10:30 AM UTC.