FELT EARTHQUAKES IN MANU'A ISLANDS, AMERICAN SAMOA

Earthquakes have been felt by residents of the Manuʻa group of islands, American Samoa, since late July 2022, and are ongoing.  Current seismicity is 20 earthquakes/hour.

Most too small to be felt.  Level is unchanged since 16 August. 

Seismic data indicate that earthquakes are related to magma moving beneath the Manu’a Islands, likely closer to Taʻu island rather than Ofu-Olosega, and are not related to Vailulu'u seamount. Satellite data from the past 24 hours showed fairly clear views and no signs of volcanic activity. 

Seismicity recorded at Olosega Village (18 Aug 2022)

Not all earthquake swarms on volcanoes result in eruptions. Current low-level seismicity may continue and vary in intensity for days to months or longer without an eruption. It is also possible that the swarm is a precursor to an eruption. At this time, it is not known which is more likely. 

A large explosive eruption similar to the Tonga eruption on 15 January 2022 is extremely unlikely due to the different volcano formation process.

The National Weather Service in Pago Pago, USGS Volcano Hazards Program, NOAA Pacific Tsunami Warning Center, UNESCO/IOC-NOAA International Tsunami Information Center, and USGS National Earthquake Information Center are working together with the American Samoa DHS Emergency Operations Center (EOC) to understand the source of these earthquakes better.  
The Samoa Meteorological Service is also reporting increased seismicity south or east of Tutuila Island.

VOLCANOES IN AMERICAN SAMOA (USGS Taū, American Samoa web site)
The U.S. Geological Survery’s Volcano Hazards Program is responsible for monitoring volcanoes in American Samoa. 

INFORMATION STATEMENTS (USGS, NOAA)
Details on the felt earthquakes, analysis, and response, and volcano science
10 August 2022
12 August 2022
13 August 2022
14 August 2022
15 August 2022 
16 August 2022
17 August 2022
18 August 2022
19 August forward, Volcano Updates,  Subscribe to Volcano Notification Service  

TSUNAMI WARNINGS IN AMERICAN SAMOA (tsunami.gov web site)
NOAA’s Pacific Tsunami Warning Center (PTWC), along with the National Weather Service in Pago Pago, are responsible for issuing tsunami alerts for American Samoa. PTWC monitors large earthquakes and will issue a warning if a dangerous tsunami is imminent. However, volcanic eruptions usually do not generate large earthquakes. Therefore, nearby coastal residents should self-evacuate upon recognizing the natural tsunami warning signs - do not wait for an official tsunami warning

If you are at the coast in American Samoa, it’s important to heed the tsunami natural warning signs. If you feel a strong or long duration earthquake, see a sudden rise or fall of the ocean, or hear a loud roar from the ocean, or see a large aerial plume from a volcanic eruption, a tsunami may follow and you should immediately move to higher ground.
For more tsunami safety and awareness information, see below.

SUMMARY (as of 22 August 2022)

• Earthquakes have been felt by residents of the Manuʻa group of islands, American Samoa, and are ongoing.  Reports from National Park of American Samoa staff and Taʻū residents suggest that the activity began on July 26th. Since August 10th, earthquakes have also been reported by residents of Ofu and Olosega islands.
  
  

• Felt Reports indicate that the earthquakes vary in intensity, but are generally short, sharp jolts. The earthquakes are more likely to be felt by people indoors at rest and along the coast, where buildings sit on sediment that amplifies shaking. These factors are probably responsible for the variability in reporting.
  
  

• One temporary seismometer (vertical motion) was installed in Fitiʻuta village on Taʻū on 13 August 2022. Another temporary seismometer was installed on Olosega village on Ofu-Olosega Island on 14 August 2022.  Both stations are currently operating intermittently, which is not unexpected for these inexpensive devices.  Better equipment is being delivered that will allow accurate locations to be determined.  
  
  

• A significant number of small earthquakes (currently 20 events/hour) have been recorded; most events are too small to be felt. Estimated magnitudes of the largest earthquakes are between magnitude 2 and 3.
  

• Shown are seismic data the seismometers on Ta'u and Ofu-Olosega islands - each vertical signal is a small local earthquake, and may be so small that they are not felt.

  Fitiʻuta village, Ta'u (14 August)
  

Seismic data for 18 August 2022

 Fitiʻuta village, Ta'u (18 August)

Olosega village, Ofu-Olosega (18 August)

• Seismic data showed that Olosega village is about twice as far from the earthquake source as Fitiʻuta village on Taʻū.  The source appears to somewhere in a 10-12 km radius from the Fitiʻuta seismometer and 20-25 km from the Olosega seismomete (note distances also include the depth in the Earth).  The overlap of these two distances suggest that the source is much closer to and probably somewhere beneath Taʻū island or itʻs submerged flanks.
  
  

• Taʻū, Ofu-Olosega, and Vailuluʻu volcanoes are located on the crest of the Samoan Ridge, a predominantly submarine feature formed from volcanic activity associated with the Samoa hotspot.  The volcanoes typically erupt as slow-moving lava flows and low-level eruptions.  A vent that erupted between Ta‘ū and Ofu-Olosega in 1866 could have been related to either volcano. Vailuluʻu is a submarine seamount whose summit is about 1970 feet (600 m) below sea level. The last eruption of Vailuluʻu was in 2003, during which a cone formed within the summit caldera
  
  

• A large explosive eruption, like the Hunga Tonga-Hunga Ha'apai volcanic eruption in Tonga earlier this year, is extremely unlikely due to the different volcano formation process (hotspot vs. subduction as the Pacific Plate subducts beneath the Indo-Australian Plate).

American Samoa Dept of Homeland Security, Facebook
Earthquake, Tsunami Safety information: 
• Protecting yourself and your family from earthquake (USGS)
• American Samoa Tsunami Awareness Information (ITIC) (this page)
• Protecting yourself and your family from tsunami (NOAA)

Volcano information: 

Tsunami information: 

TSUNAMI AWARENESS INFORMATION:

Tsunami Sources Affecting American Samoa  (ITIC, NCEI, 2022) (JPG, 627 KB)

Tsunami Observations in American Samoa  (ITIC, NCEI, 2022) (JPG, 669 KB)

Historical Tsunami Effects, American Samoa, Samoa, Tonga 24" x 36", English (update, draft Aug 2022) (English PDF, 1.92 MB)

Tsunami Warning! comic book American Samoa, New Hebrides Trench (ITIC 2019) (English PDF (30 MB), low res)

Natural Tsunami Warnings and Official Tsunami Warnings  (JPG, 405 KB)

Earthquake and Tsunami Safety (JPG, 501 KB)

Samoa Islands Earthquake and Tsunami  Effects in American Samoa 29 September 2009, 1748 UTC, Mw 8.1 (video, ITIC 2018, update 2022), silent

TsunamiTeacher USA, Basics (video, ITIC 2011) Samoan