Very strong shallow earthquake near Niuafo’ou volcano (Tonga) – NO special volcanic activity reported

Last update: September 23, 2011 at 1:04 am by By

Article also compiled by Carlos Robles
Earthquake overview :  Very strong earthquake near a rim volcano island in Tonga. As this earthquake is extremely shallow and as the location of the epicenter has a substantial error margin, we feared for volcanic activity.

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To read the full story as it happened, we advise our readers to start at the lower part of the page (earthquake data).

Keep this page open or return regularly as we will be back with more details when they become available

NOAA tsunami message for the Pacific :
NO DESTRUCTIVE WIDESPREAD TSUNAMI THREAT EXISTS BASED ON HISTORICAL EARTHQUAKE AND TSUNAMI DATA

IMPORTANT UPDATE 00:57 UTC :
Matangi reports : The earthquake was felt by Niuafo'ou residents. Meola Vaka at the Western Union office at 'Esia said she felt an earthquake this morning that lasted for less than a minute. She said there was no unusual volcanic activity evident on the island.

Update 23/09 – 00:11 UTC : Both EMSC and USGS have epicenters approx. 30 to 40 km from the volcanic island.  If the epicenter locations are accurate which we do not know at the moment, it may be well a normal earthquake close to a volcano.

Update 23/09 – 00:11 UTC : The latest known eruption from the volcano was in 1985.

Update 23/09 – 00:04 UTC : Between 1946 and 1947, the island was completely evacuated by the Tongan government following a volcanic eruption. In 1957 about half of the population returned to Niuafo'ou, and the rest remained in 'Eua (source Wikipedia)

Update 23:59 UTC : As this earthquake is extremely shallow and as the location of the epicenter has a substantial error margin, we do not exclude volcanic activity.

Update 23:54 UTC :  Max shaking on the island would be a VI MMI strong shaking.

Update 23:49 UTC : Niuafo'ou is is a volcanic rim island of 15 km² and with a population of 650 in 2006

Update 23:43 UTC : Earthquake values from the other seismological agencies :
EMSC : 6.5 @ 2 km
GFZ : 6.1 @ 5 km

Update 23:32 UTC : We change our opinion because in lowering the magnitude, also the location has been recalculated. The epicenter is now located approx. 30 km from Niuafo'ou, a small 7 km diameter island.  The island has a ring road and a number of small settlements. As this earthquake was also very shallow (less than 10 km, there is a small chance on minor damage).

Update 23:29 UTC : USGS has decreased the Magnitude to 6.2, which is even safer than the initial 6.8.
Conclusion : Harmless earthquake amidst a lot of water

"I Have Felt It" reports as received by Earthquake-Report.com
MMI values (if indicated) after the text (III: Weak shaking, IV Light shaking, V Moderate shaking, VI Strong shaking, VII Very Strong shaking)
- No Felt reports as yet, be the first to send us what you experienced.

Most important Earthquake Data:
Magnitude :  6.2 Mw
UTC Time : Thursday, September 22, 2011 at 23:07:03 UTC
Local time at epicenter : Friday, September 23, 2011 at 12:07:03 PM at epicenter
Depth (Hypocenter) : 8.6 km (EMSC 2 km) (GFZ 5 km)
Geo-location(s) :
Close to Niuafo'ou (Tonga)
382 km (238 miles) NNW (338°) from Neiafu, Tonga
 

Links to important maps
USGS Did You Feel It Map
Google satellite map showing the epicenter and the surrounding area.
Historic earthquakes map
Seismic hazard map
Shaking map
Focal mechanism report
Human impact map
GDACS earthquake report
NOAA tsunami report

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I did feel it – Ik heb het gevoeld – Το έκανα αισθάνεται –Yo lo he sentido – 我的确感到了 – 私はそれを感じていました- Ich habe es gefühlt – Bunu hissediyorum yaptı – لم أشعر أنه

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Tell us where in which location you felt the earthquake
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Your Email address might help us if we request for additional details about your experience. This field is NOT mandatory. It is up to you to give it or not.
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People :
Felt by persons at rest, on upper floors or favorably placed.
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People :
Felt indoors; hanging objects may swing, vibration similar to passing of light trucks, duration may be estimated, may not be recognized as an earthquake.
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People :
Generally noticed indoors but not outside. Light sleepers may be awakened. Vibration may be likened to the passing of heavy traffic, or to the jolt of a heavy object falling or striking the building.
Fittings :
Doors and windows rattle. Glassware and crockery rattle. Liquids in open vessels may be slightly disturbed. Standing motorcars may rock.
Structures :
Walls and frames of buildings, and partitions and suspended ceilings in commercial buildings, may be heard to creak.
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People :
Generally felt outside, and by almost everyone indoors. Most sleepers awakened. A few people alarmed.
Fittings :
Small unstable objects are displaced or upset. Some glassware and crockery may be broken. Hanging pictures knock against the wall. Open doors may swing. Cupboard doors secured by magnetic catches may open. Pendulum clocks stop, start, or change rate.
Structures :
Some large display windows cracked. A few earthenware toilet fixtures cracked.
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People Felt by all. People and animals alarmed. Many run outside. Difficulty experienced in walking steadily.
Fittings :
Objects fall from shelves. Pictures fall from walls. Some furniture moved on smooth floors, some unsecured free-standing fireplaces moved. Glassware and crockery broken. Very unstable furniture overturned. Small church and school bells ring. Appliances move on bench or table tops. Filing cabinets or "easy glide" drawers may open (or shut).
Structures :
Slight damage to buildings with low standard. Some stucco or cement plaster falls. Large display windows broken. Damage to a few weak domestic chimneys, some may fall.
Environment :
Trees and bushes shake, or are heard to rustle. Loose material may be dislodged from sloping ground, e.g. existing slides, talus slopes, shingle slides.
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People
General alarm. Difficulty experienced in standing. Noticed by motorcar drivers who may stop.
Fittings :
Large bells ring. Furniture moves on smooth floors, may move on carpeted floors. Substantial damage to fragile contents of buildings.
Structures :
Unreinforced stone and brick walls cracked. Low standard buildings cracked with some minor masonry falls. A few instances of damage to buildings of ordinary workmanship. Unbraced parapets, unbraced brick gables, and architectural ornaments fall. Roofing tiles, especially ridge tiles may be dislodged. Many unreinforced domestic chimneys damaged, often falling from roof-line. Water tanks Type I burst. A few instances of damage to brick veneers and plaster or cement-based linings. Unrestrained water cylinders (hot-water cylinders) may move and leak. Some common windows cracked. Suspended ceilings damaged.
Environment :
Water made turbid by stirred up mud. Small slides such as falls of sand and gravel banks, and small rock-falls from steep slopes and cuttings. Instances of settlement of unconsolidated or wet, or weak soils. Some fine cracks appear in sloping ground. A few instances of liquefaction (i.e. small water and sand ejections).
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People Alarm may approach panic. Steering of motorcars greatly affected. Structures : Low standard buildings heavily damaged, some collapse. ordinary workmanship buildings damaged, some with partial collapse. Reinforced masonry or concrete buildings damaged in some cases. A few instances of damage to buildings and bridges designed and built to resist earthquakes. Monuments and pre-1976 elevated tanks and factory stacks twisted or brought down. Some pre-1965 infill masonry panels damaged. A few post-1980 brick veneers damaged. Decayed timber piles of houses damaged. Houses not secured to foundations may move. Most unreinforced domestic chimneys damaged, some below roof-line, many brought down. Environment : Cracks appear on steep slopes and in wet ground. Small to moderate slides in roadside cuttings and unsupported excavations. Small water and sand ejections and localized lateral spreading adjacent to streams, canals, lakes, etc.
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Structures Many low standard buildings destroyed. Ordinary workmanship buildings heavily damaged, some collapse. Reinforced masonry or concrete buildings damaged, some with partial collapse. Buildings and bridges designed and built to resist earthquakes damaged in some cases, some with flexible frames seriously damaged. Damage or permanent distortion to some buildings and bridges, designed and built to normal use standards. Houses not secured to foundations shifted off. Brick veneers fall and expose frames. Environment : Cracking of ground conspicuous. Landsliding general on steep slopes. Liquefaction effects intensified and more widespread, with large lateral spreading and flow sliding adjacent to streams, canals, lakes, etc.
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