Magnitude 7.9 quake strikes Alaska: macroseismic analysis

MeteoWeb

exposure_smallThe magnitude-7.9 earthquake was centered about 13 miles (21 kilometers) southeast of Little Sitkin Island, or about 1,400 miles (2,250 kilometers) southwest of Anchorage. There were no reports of damage, said Jeremy Zidek, a spokesman for the Alaska Department of Homeland Security and Emergency Management. About 200 miles (320 kilometers) west, a tsunami wave of about 7 inches (18 centimeters) was reported at Amchitka Island, Zidek said. The wave diminished the further it traveled, reaching only a couple of inches at Adak and Shemya. But the earthquake was widely felt in Adak, one of the largest cities in the affected area. Shaking could also be felt in Shemya and other villages along the island chain. Monday’s earthquake was initially reported with a magnitude of 7.1, but that was upgraded to 8.0, said Natasha Ruppert, a seismologist with the Alaska Earthquake Center. In the review of data hours after the quake, the magnitude was downgraded to 7.9. There were several strong aftershocks, with magnitudes reaching 5.9. Dave Nyland, a geophysicist at the National Tsunami Warning Center, said those would be too small to trigger a tsunami.

Macroseismic analysis

Earthquake epicenter: Little Sitkin island – Alaska – USA
Date 23/06/2014 UTC 20:53:09
Latitude 51.80° N Longitude 178.76° E
Magnitude 7.9 Depth 107.5 Km
The following analysis shows the macroseismical effects based on a model hereby displayed. The reported macroseismic effects may vary (one or two levels, up or down) depending on the characteristics of local geology or buildings. If not expressly indicated, earthquake perception is intended during the day. Peak ground acceleration is expressed in cm/s².
Values and terms do not coincide with other seismic scales.
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usc000rki5_ciimNearby cities 80 Km far from the epicenter:
Little Sitkin island – Alaska
10- Harmful earthquake 150 < PGA < 300 ( VII MCS )
Seismic shake is very strong; people who drive on bumpy roads may not feel it. The event is preceeded by an intense and wide roar, often heard inside buildings. All objects, mirrors, glasses, fall down and break inside houses; furniture moves. People panic and run outside. There are just a few victims and injured. The structure of old houses and monuments is damaged; big cracks in walls; doors and windows break; tiles and chimneys break and fall. Ordinary buildings have shallow damages and can be accessed. A few cracks on the ground; only a few roads get damaged. Even if the situation is serious, a lot of reports come from the affected area.
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Nearby cities from 80 Km to 194 Km far from the epicenter:
Islands Alaska
9- Strong earthquake 80 < PGA < 150 ( VI MCS )
Seismic shake is intense and only a few people, inside moving vehicles, can’t feel it. The event is preceeded by a roar, often heard even inside the houses; who sleeps, wakes up. Furniture and objects vibrate loudly; unsteady objects fall. Doors and windows open and close. Chandeliers oscillate widely. People are terrified and run out of buildings. Someone gets hurt or is suddenly taken ill. Old buildings are damaged: cracks in walls; broken windows; broken chimneys. Ordinary buildings are not particularly damaged. A high number of reports arrive through the internet.
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intensityNearby cities from 194 Km to 349 Km far from the epicenter:
Islands Alaska
8- Notable earthquake 40 < PGA < 80 ( V MCS )
Inside the houses almost everyone feels the earthquake, and sometimes even the preceeding roar; outside many perceive a vibration. Seismic shake is intense and wakes up several people. Objects vibrate, some of them fall. Chandeliers oscillate widely. Doors and windows open and close. People are scared and run out of buildings. Old houses and monuments are lightly damaged. Several reports arrive from the affected area.
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Nearby cities from 349 Km to 592 Km far from the epicenter:
Islands Alaska
7- Moderate earthquake 20 < PGA < 40 ( IV MCS )
Inside the houses, many people feel the earthquake. Seismic vibration is very intense and wakes up who’s sleeping. Chandeliers oscillate widely. Windows and objects shake;People are scared; many of them get out of buildings. Outside many people clearly feel the earthquake and hear the preceeding roar. Buildings are not externally damaged. Many reports arrive from the affected area.
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Nearby cities from 592 Km to 986 Km far from the epicenter:
Islands Alaska
6- Mild earthquake 10 < PGA < 20 ( III – IV MCS )
Lots of people inside buildings feel a strong seismic vibration. Chandeliers oscillate noticeably; crakles and tinkles can be heard. Someone of those who sleep, wakes up. Several people prefer to go outside, as a safety measure. Outside several people feel the vibration, they clearly hear that particular sound preceeding the earthquake. Many reports arrive through the internet.
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Nearby cities from 986 Km to 1632 Km far from the epicenter:
Russia: Petropavlovsk-Kamchactskiy, Vilyuchinsk, Yelizovo
5- Light earthquake 5 < PGA < 10 ( III MCS )
Inside buildings, some people feel a vibration. Chandeliers oscillate; A tinkle of glasses shattered can be heard. Someone decides to go outside, as a safety measure. Outside only a few people feel the earthquake; before the event, a few people hear a noise, like a far away thunder. From the affected area many reports arrive.
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Nearby cities from 1632 Km to 2695 Km far from the epicenter:
Anchorage, Fairbanks, Magadan
4- Weak earthquake 2.5 < PGA < 5.0 ( II – III MCS )
A relevant number of people, inside buildings in in quietness, feels a moderate vibration. Chandeliers oscillate; a tinkle of glasses shattering can be heard. People who perceive these effects feel apprehension. Outside, only a few people feel the earthquake; someone hears a low frequency noise. A few reports arrive through the internet.
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Nearby cities from 2695 Km to 4446 Km far from the epicenter:
Tokyo, Honolulu, Seoul, Juneau, Whitehorse
3- Tenuous earthquake 1.2 < PGA < 2.5 ( II MCS )
In the higest and middle floors, a few people perceive a light vibration. Chandeliers oscillate. People feel apprehension. Outside, almost nobody feels the earthquake.From the affected area, only a few reports arrive; sometimes a light sound is heard.
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Nearby cities from 4446 Km to 7331 Km far from the epicenter:
Los Angeles, San Francisco, Beijing, Toronto, Ulaanbaatar
2- Insignificant earthquake 0.6 < PGA < 1.2 ( I – II MCS )
In the highest floors and in quietness, a few people feel a very light vibration, but there isn’t any concern. Outside nobody feels anything. No sound of the earthquake can be heard. Only a few reports arrive through the internet.
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Nearby cities from 7331 Km to 12088 Km far from the epicenter:
New York, Moskva, Sydney, Roma, Parigi, New Delhi, Cairo, Caracas, Ciudad de Mexico
1- Unperceivable earthquake 0.3 < PGA < 0.6 ( I MCS )
The intensity is irrelevant; the earthquake is recorded by seismic stations in the region. Even in the best-case scenario, almost nobody feels the shaking, not even in the highest floors. No reports come from the area.
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Cities beyond 12088 Km from the epicenter.
0- Instrumental earthquake PGA < 0.3 ( I MCS )
Earthquake is unsubstantial; it is recorded by seismic stations with advanced instruments. Even in the best-case scenario, people don’t feel the earthquake.
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