Powerful M7.9 earthquake hits Gulf of Alaska, triggers tsunami warnings

A massive earthquake registered by the USGS as M7.9 hit the Gulf of Alaska at 09:31 UTC on January 23, 2018 (00:31 local time). The agency is reporting a depth of 25 km (15.5 miles). EMSC is reporting M8.0 at a depth of 10 km (6.2 miles). Tsunami warnings, watches and advisories were issued following the quake.  Over the next 3 hours, the USGS registered more than 20 aftershocks with magnitudes ranging from 2.5 to 5.3.

The epicenter was located 260.2 km (161.7 miles) SE of Chiniak (population 47) and 576.7 km (358.3 miles) S of Anchorage (population 291 826), Alaska, United States.

There are no people living within 100 km (62 miles). Some 14 000 people are estimated to have felt 14 000 light shaking.

Based on the preliminary earthquake parameters, widespread hazardous tsunami waves are possible, PTWC said 09:43 UTC.

PRELIMINARY EARTHQUAKE PARAMETERS
---------------------------------

  * MAGNITUDE      8.0
  * ORIGIN TIME    0932 UTC JAN 23 2018
  * COORDINATES    56.0 NORTH  149.2 WEST
  * DEPTH          19 KM / 12 MILES
  * LOCATION       GULF OF ALASKA


EVALUATION
----------

  * AN EARTHQUAKE WITH A PRELIMINARY MAGNITUDE OF 8.0 OCCURRED IN
    THE GULF OF ALASKA AT 0932 UTC ON TUESDAY JANUARY 23 2018.

  * BASED ON THE PRELIMINARY EARTHQUAKE PARAMETERS... WIDESPREAD
    HAZARDOUS TSUNAMI WAVES ARE POSSIBLE.


TSUNAMI THREAT FORECAST
-----------------------

  * HAZARDOUS TSUNAMI WAVES FROM THIS EARTHQUAKE ARE POSSIBLE
    WITHIN THE NEXT THREE HOURS ALONG SOME COASTS OF

      NO AREAS COVERED BY THIS MESSAGE APPEAR TO BE IMMEDIATELY
      THREATENED. HOWEVER... THE SITUATION IS STILL UNDER
      INVESTIGATION. THIS THREAT EVALUATION WILL BE UPDATED AS
      SOON AS FURTHER INFORMATION BECOMES AVAILABLE.


RECOMMENDED ACTIONS
-------------------

  * GOVERNMENT AGENCIES RESPONSIBLE FOR THREATENED COASTAL AREAS
    SHOULD TAKE ACTION TO INFORM AND INSTRUCT ANY COASTAL
    POPULATIONS AT RISK IN ACCORDANCE WITH THEIR OWN
    EVALUATION... PROCEDURES AND THE LEVEL OF THREAT.

  * PERSONS LOCATED IN THREATENED COASTAL AREAS SHOULD STAY ALERT
    FOR INFORMATION AND FOLLOW INSTRUCTIONS FROM NATIONAL AND
    LOCAL AUTHORITIES.


POTENTIAL IMPACTS
-----------------

  * A TSUNAMI IS A SERIES OF WAVES. THE TIME BETWEEN WAVE CRESTS
    CAN VARY FROM 5 MINUTES TO AN HOUR. THE HAZARD MAY PERSIST
    FOR MANY HOURS OR LONGER AFTER THE INITIAL WAVE.

  * IMPACTS CAN VARY SIGNIFICANTLY FROM ONE SECTION OF COAST TO
    THE NEXT DUE TO LOCAL BATHYMETRY AND THE SHAPE AND ELEVATION
    OF THE SHORELINE.

  * IMPACTS CAN ALSO VARY DEPENDING UPON THE STATE OF THE TIDE AT
    THE TIME OF THE MAXIMUM TSUNAMI WAVES.

  * PERSONS CAUGHT IN THE WATER OF A TSUNAMI MAY DROWN... BE
    CRUSHED BY DEBRIS IN THE WATER... OR BE SWEPT OUT TO SEA.

As of 12:35 AKST, a Tsunami Warning is in effect for:

BRITISH COLUMBIA, The Juan de Fuca Strait coast, the outer west coast of Vancouver Island, the central coast and northeast Vancouver Island, and the north coast and Haida Gwaii

SOUTHEAST ALASKA, The inner and outer coast from The BC/Alaska Border to Cape Fairweather, Alaska (80 miles SE of Yakutat)

SOUTH ALASKA AND THE ALASKA PENINSULA, Pacific coasts from Cape Fairweather, Alaska (80 miles SE of Yakutat) to Unimak Pass, Alaska (80 miles NE of Unalaska)

ALEUTIAN ISLANDS, Unimak Pass, Alaska (80 miles NE of Unalaska) to Attu, Alaska including the Pribilof Islands

A Tsunami Watch is in effect for:

CALIFORNIA, The coast from The Cal./Mexico Border to The Oregon/Cal. Border including San Francisco Bay

OREGON, The coast from The Oregon/Cal. Border to The Oregon/Wash. Border including the Columbia River estuary coast

WASHINGTON, Outer coast from the Oregon/Washington border to Slip Point, Columbia River estuary coast, and the Juan de Fuca Strait coast

BULLETIN
Public Tsunami Message Number 1
NWS National Tsunami Warning Center Palmer AK
1235 AM AKST Tue Jan 23 2018

...A TSUNAMI WARNING IS NOW IN EFFECT...


...A TSUNAMI WATCH IS NOW IN EFFECT...


Tsunami Warning in Effect for;

 * BRITISH COLUMBIA, The Juan de Fuca Strait coast, the outer
   west coast of Vancouver Island, the central coast and
   northeast Vancouver Island, and the north coast and Haida
   Gwaii

 * SOUTHEAST ALASKA, The inner and outer coast from The
   BC/Alaska Border  to Cape Fairweather, Alaska (80 miles SE
   of Yakutat)

 * SOUTH ALASKA AND THE ALASKA PENINSULA, Pacific coasts from
   Cape Fairweather, Alaska (80 miles SE of Yakutat) to Unimak
   Pass, Alaska (80 miles NE of Unalaska)

 * ALEUTIAN ISLANDS, Unimak Pass, Alaska (80 miles NE of
   Unalaska) to Attu, Alaska including the Pribilof Islands


Tsunami Watch in Effect for;

 * CALIFORNIA, The coast from The Cal./Mexico Border  to The
   Oregon/Cal. Border  including San Francisco Bay

 * OREGON, The coast from The Oregon/Cal. Border  to The
   Oregon/Wash. Border  including the Columbia River estuary
   coast

 * WASHINGTON, Outer coast from the Oregon/Washington border
   to Slip Point, Columbia River estuary coast, and the Juan
   de Fuca Strait coast


PRELIMINARY EARTHQUAKE PARAMETERS
---------------------------------
 * The following parameters are based on a rapid preliminary
   assessment and changes may occur.

 * Magnitude      8.0
 * Origin Time    0032 AKST Jan 23 2018
                  0132  PST Jan 23 2018
                  0932  UTC Jan 23 2018
 * Coordinates    56.0 North 149.2 West
 * Depth          12 miles
 * Location       175 miles SE of Kodiak City, Alaska
                  365 miles S of Anchorage, Alaska


FORECASTS OF TSUNAMI ACTIVITY
-----------------------------
 * Tsunami activity is forecasted to start at the following
   locations at the specified times.

                 FORECAST
                 START
SITE             OF TSUNAMI
----             ----------

 * Alaska
Kodiak           0145 AKST Jan 23
Seward           0155 AKST Jan 23
Elfin Cove       0155 AKST Jan 23
Sitka            0200 AKST Jan 23
Yakutat          0205 AKST Jan 23
Valdez           0215 AKST Jan 23
Sand Point       0220 AKST Jan 23
Cordova          0225 AKST Jan 23
Unalaska         0240 AKST Jan 23
Homer            0255 AKST Jan 23
Craig            0300 AKST Jan 23
Cold Bay         0300 AKST Jan 23
Adak             0305 AKST Jan 23
Shemya           0350 AKST Jan 23
Saint Paul       0400 AKST Jan 23

 * British Columbia
Langara          0210 AKST Jan 23
Tofino           0340 AKST Jan 23

 * Washington
Neah Bay         0455  PST Jan 23
Long Beach       0500  PST Jan 23
Moclips          0500  PST Jan 23
Westport         0510  PST Jan 23
Port Angeles     0530  PST Jan 23
Port Townsend    0555  PST Jan 23

 * Oregon
Port Orford      0505  PST Jan 23
Charleston       0510  PST Jan 23
Seaside          0510  PST Jan 23
Newport          0515  PST Jan 23
Brookings        0515  PST Jan 23

 * California
Crescent City    0520  PST Jan 23
Horse Mountain   0525  PST Jan 23
Fort Bragg       0525  PST Jan 23
Monterey         0555  PST Jan 23
San Francisco    0620  PST Jan 23
Port San Luis    0620  PST Jan 23
Santa Barbara    0635  PST Jan 23
Los Angeles Harb 0650  PST Jan 23
Newport Beach    0700  PST Jan 23
La Jolla         0705  PST Jan 23
Oceanside        0705  PST Jan 23


OBSERVATIONS OF TSUNAMI ACTIVITY
--------------------------------
 * No tsunami observations are available to report.


RECOMMENDED ACTIONS
-------------------
Actions to protect human life and property will
vary within tsunami warning areas.

If you are in a tsunami warning area;

 * Evacuate inland or to higher ground above and beyond
   designated tsunami hazard zones or move to an upper floor
   of a multi-story building depending on your situation.

 * Move out of the water, off the beach, and away from
   harbors, marinas, breakwaters, bays and inlets.

 * Be alert to and follow instructions from your local
   emergency officials because they may have more detailed or
   specific information for your location.

 * If you feel a strong earthquake or extended ground rolling
   take immediate protective actions such as moving inland
   and/or uphill preferably by foot.

 * Boat operators,
     * Where time and conditions permit, move your boat out to
       sea to a depth of at least 180 feet.

     * If at sea avoid entering shallow water, harbors,
       marinas, bays, and inlets to avoid floating and
       submerged debris and strong currents.

 * Do not go to the shore to observe the tsunami.

 * Do not return to the coast until local emergency officials
   indicate it is safe to do so.

If you are in a tsunami watch area;

 * Prepare to take action and stay alert for further
   information.


IMPACTS
-------
Impacts will vary at different locations in the warning
areas.

If you are in a tsunami warning area;

 * A tsunami with damaging waves and powerful currents is
   possible.

 * Repeated coastal flooding is possible as waves arrive
   onshore, move inland, and drain back into the ocean.

 * Strong and unusual waves, currents and inland flooding
   can drown or injure people and weaken or destroy structures
   on land and in water.

 * Water filled with floating or submerged debris that can
   injure or kill people and weaken or destroy buildings and
   bridges is possible.

 * Strong and unusual currents and waves in harbors,
   marinas, bays, and inlets may be especially
   destructive.

 * Some impacts may continue for many hours to days after
   arrival of the first wave.

 * The first wave may not be the largest so later waves may
   be larger.

 * Each wave may last 5 to 45 minutes as a wave encroaches
   and recedes.

 * Coasts facing all directions are threatened because the
   waves can wrap around islands and headlands and into bays.

 * Strong shaking or rolling of the ground indicates an
   earthquake has occurred and a tsunami may be imminent.

 * A rapidly receding or receded shoreline, unusual waves and
   sounds, and strong currents are signs of a tsunami.

 * The tsunami may appear as water moving rapidly out to sea,
   a gentle rising tide like flood with no breaking wave,
   as a series of breaking waves, or a frothy wall of water.


ADDITIONAL INFORMATION AND NEXT UPDATE
--------------------------------------
 * Refer to the internet site tsunami.gov for more information.

 * Pacific coastal residents outside California, Oregon,
   Washington, British Columbia and Alaska should refer to the
   Pacific Tsunami Warning Center messages at tsunami.gov.

 * This message will be updated within 30 minutes.

$$

Estimated population exposure to earthquake shaking

The USGS issued a green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are unreinforced brick masonry and reinforced masonry construction.

Regional seismicity

Updates

At 12:13 UTC (03:13 AKST), the Tsunami Advisory was canceled for the coastal areas of South Alaska and the Alaska Peninsula. Residents are advised not to re-occupy hazard zones until local emergency officials indicate it is safe to do so.

Some areas may continue to see small sea level changes.

BULLETIN
Public Tsunami Message Number 7
NWS National Tsunami Warning Center Palmer AK
413 AM AKST Tue Jan 23 2018

...THE TSUNAMI ADVISORY IS CANCELLED...

 * The Tsunami Advisory is canceled for the coastal areas of
   South Alaska and the Alaska Peninsula


OBSERVATIONS OF TSUNAMI ACTIVITY - UPDATED
------------------------------------------
 * Observed max tsunami height is the highest recorded water level
   above the tide level up to the time of this message.

                                  TIME               OBSERVED MAX
 SITE                         OF MEASUREMENT         TSUNAMI HEIGHT
 ---------------------------- ----------------       --------------
 Kodiak  Alaska               0329  PST Jan 23           0.6ft
 Seward  Alaska               0331  PST Jan 23           0.4ft
 Old Harbor  Alaska           0338  PST Jan 23           0.7ft
 Sitka  Alaska                0318  PST Jan 23           0.4ft
 Yakutat  Alaska              0335  PST Jan 23           0.5ft
 Langara  BC                  0330  PST Jan 23           0.4ft


RECOMMENDED ACTIONS - UPDATED
-----------------------------
 * Do not re-occupy hazard zones until local emergency officials 
   indicate it is safe to do so. 


IMPACTS - UPDATED
-----------------
 * A tsunami was generated by this event, but no longer 
   poses a threat. 

 * Some areas may continue to see small sea level changes. 

 * The determination to re-occupy hazard zones must be made 
   by local officials. 


ADDITIONAL INFORMATION AND NEXT UPDATE
--------------------------------------
 * Refer to the internet site tsunami.gov for more information. 

 * Pacific coastal regions outside California, Oregon, 
   Washington, British Columbia, and Alaska should refer to the 
   Pacific Tsunami Warning Center messages at tsunami.gov. 

 * This will be the final U.S. National Tsunami Warning Center 
   message issued for this event. 

$$

Between 09:31 and 12:48 UTC, the USGS registered a total of 24 earthquakes in this region, including M7.9. Magnitudes ranged from 2.5 to 7.9.

Image credit: USGS

Featured image credit: USGS