Summary

• Earthquakes have been felt by residents of Taʻū (the largest of the Manuʻa group of islands) in American Samoa, for a few days and are ongoing. 

• A team of experts is working on understanding the cause of these earthquakes and will share more information when it is available in another Information Statement. 

• There is a chance these earthquakes are caused by volcanic activity, but an eruption like Hunga Tonga–Hunga Ha'apai in Tonga earlier this year is extremely unlikely. 

• If you are on the coast in American Samoa and feel a strong or long earthquake, see a sudden rise or fall of the ocean or hear a loud roar from the ocean, a tsunami may follow, and you should immediately move to higher ground. 

• The U.S. Geological Survey Hawaiian Volcano Observatory is responsible for monitoring volcanoes in American Samoa. Current seismic monitoring capabilities are limited to a station in Apia, and the U.S. Geological Survey is working on a plan to extend seismic monitoring to the island of Taʻū. 

• Residents can greatly assist these monitoring efforts by reporting accurate times that earthquake shaking is felt to the National Weather Service Office in Pago Pago. 

Details

Since the end of last week, the Pago Pago National Weather Service office has received reports of earthquakes felt by residents of Taʻū (the largest of the Manuʻa group of islands in the South Pacific Ocean), American Samoa. Experts at the Pago Pago National Weather Service office, U.S. Geological Survey (USGS) Hawaiian Volcano Observatory (HVO), National Oceanic and Atmospheric Administration (NOAA) Pacific Tsunami Warning Center (PTWC), NOAA-IOC International Tsunami Information Center, and USGS National Earthquake Information Center are working together to understand better the source of these earthquakes, which are ongoing.  

The real-time earthquake-monitoring network does not currently permit the earthquake magnitudes or locations to be determined precisely. However, given that they are being felt and there are no reports of widespread damage, we expect these earthquakes to be less than magnitude 4. Earthquakes of this magnitude may cause weak to moderate ground shaking but do not typically cause damage to buildings or infrastructure. 

At this stage, we cannot confirm where the earthquakes are located. There have been prior earthquake swarms and volcanic activity at Vailuluʻu, an underwater volcano 25 miles (40 kilometers) east of Taʻū that last erupted in 2003.  

Hazard Implications 

We do not expect a large explosive eruption like that of Hunga Tonga–Hunga Ha'apai in Tonga earlier this year because volcanoes in the two places form from two very different earth processes. Like in Hawaii, American Samoa volcanoes are caused by a hotspot—eruptions typically include slow-moving lava flows and low-level explosions of lava localized to a small area. Volcanoes in Tonga are caused by the subduction of the Pacific Plate underneath the Indo-Australia Plate, which are more explosive and can produce far-reaching ash clouds. Highly explosive activity is not typical of hotspot volcanoes. 

A tsunami could potentially happen due to a fast-occurring and large underwater eruption or a submarine landslide at Vailuluʻu. The Pacific Tsunami Warning Center will issue warnings if necessary. However, any potential tsunami would travel quickly to the surrounding islands. Therefore, residents of the Manuʻa islands and elsewhere in American Samoa would probably see the tsunami before receiving any official warning.  

If you are at the coast and feel a strong or long earthquake, see a sudden rise or fall of the ocean, or hear a loud roar from the ocean, a tsunami may follow. Immediately move to higher ground.   

Here is information on what you can do to protect yourself and your family if you see a tsunami or receive a warning: https://www.weather.gov/safety/tsunami-during. 

American Samoa volcanoes are monitored remotely with satellite data and a distant seismic station from Apia, Samoa. These observations might detect significant explosive activity in American Samoa. Unfortunately, we cannot provide advanced warning of activity because there is currently an absence of more localized ground-based monitoring stations at the volcanoes.  

We will provide additional information as it becomes available. 

More information

• National Weather Service Pago Pago Office: https://www.weather.gov/ppg/wsopagooffice  

• National Park of American Samoa: https://www.nps.gov/npsa/index.htm 

• International Tsunami Information Center: http://itic.ioc-unesco.org/index.php

• Pacific Tsunamic Warning Center: https://tsunami.gov/

• Protecting yourself and your family from earthquakes: https://www.usgs.gov/node/277816  

• Protecting yourself and your family from tsunami: https://www.weather.gov/safety/tsunami 

• Subscribe to U.S. Tsunami Warning Center: https://www.tsunami.gov/?page=productRetrieval  

•  Smithsonian Institution Global Volcanism Program webpage on Taʻū Island: https://volcano.si.edu/volcano.cfm?vn=244001

• Smithsonian Institution Global Volcanism Program webpage on Vailuluʻu: https://volcano.si.edu/volcano.cfm?vn=244000 

How you can help scientists: 

Contact askhvo@usgs.gov if you have information or observations to share, such as unusual changes in the ground, ocean, or new large areas of dead vegetation or wildlife. These are most useful if you include when and where you observed this and have a photo or video to share that conveys what you see and the scale. A person, boat, house, or tree can provide scale. Only take a photo or video if it is safe to do so. 

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