The people of Alaska awoke to a normal cold Bank Holiday, and it continued that way as far as anyone could tell, until 5.36pm local time (3.36on 27th March UTC.)
At that time, some 14 miles below Prince William Sound, approximately 80 miles east of Anchorage, near College Fjiord, the Pacific Plate and the North American Plate fractured with magnitude on the Richter Scale of 8.5 and a Moment Magnitude of 9.2 [1]with the epicentre at 61.1N 147.5W.
It started with about 10 seconds of rumbling and slight movement.The Alaskan people were very used to this and really took little notice.
Then the ground started to ripple and heave with surface waves and fissures up to 30' wide opened and closed. Glass fractured in building before the buildings themselves started to break up.
This main quake lasted four and a half minutes.It triggered landslides and avalanches, which in turn set off tsunamis; it brought down buildings and tore up roads.Bridges collapsed and beaches were raised. The rail freight yard was completely demolished.
Liquefaction[2] was the cause of many of the building in Anchorage collapsing, the shaking disturbing the sands and clay lenses below, causing their strength to drop below the stability level.
The fracture tilted an area of Alaska the size of Wales, drowning forests at one end and leaving ships grounded far from the sea at the other.Areas east of Kodiak were raised up to 30', with the town of Portage dropping over 8'.The following winter ice flows were reported floating down the main street of that town.
The greater part of the 139 deaths was due to the tsunamis which were generated by tectonic uplift of the bed of Prince William Sound, and by sub-areal and submarine landslides. The shaking caused five slide generated tsunamis within minutes after it began. These five occurred at Kachemak Bay, Seward, Whittier, and two at Valdez.
As an example and in brief summary: In Seward, a section of just over one kilometre of the water front slid into the Resurrection Bay due to the earthquake shaking. This created a local tsunami causing a great deal ofdamage and spread oil from fractured tanks which caught fire and floated on the water. About 20 minutes after this occurred, the first wave of the main tsunami arrived.
The number of tsunamis does not seem to be recorded, but it is recorded that they went on until 2 a.m. local time.
The damage was not confined to Alaska. There was earthquake damage right across the Aleutian Islands, and probably into the coastal regions of the Kamchatka Peninsular but this was the height of the Cold War, so the Soviet Union did not report it to the outside world.Those places were also hit with the tsunamis.
The shock was felt badly in Vancouver Island, Canada and Depoe, Oregon, and tremors were even felt in California.All these place were affected by the tsunami which even reached Hawai'i and Japan.
Without belittling 139 deaths it must be considered very fortunate that this was a very unpopulated area. Had it happened almost anywhere else around the Pacific Rim the loss of life might have been as catastrophic as we saw in The Anderman Islands and Indian Ocean on Boxing Day 2004.
The main severe after-shocks continued for three days, and overall it took 18 months to settle into quietness again after over 10,000
minor shocks.
1. Moment magnitude scale
From Wikipedia, the free encyclopedia
The moment magnitude scale (abbreviated as MMS; denoted as MW or M) is used by seismologists to measure the size of earthquakes in terms of the energy released.[1] The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped.[2] The scale was developed in the 1970s to succeed the 1930s-era Richter magnitude scale (ML). Even though the formulae are different, the new scale retains the familiar continuum of magnitude values defined by the older one. The MMS is now the scale used to estimate magnitudes for all modern large earthquakes by the United States Geological Survey.[3]
2. Liquefraction
From Wikipedia, the free encyclopedia
In geology, soil liquefaction refers to the process by which water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid, often in an earthquake. By undermining the foundations and base courses of infrastructure, liquefaction can cause serious damage.
N.B. For pictures of the damage, Google 'images' of 'Good Friday 1964 Alaskan earthquake' .
John.
John
“Civilisation exists by geological consent, subject to change without notice.” - Will Durant
GeologyRocks
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Bad Friday
Submitted by John on Wed, 04/09/2014 - 18:23.Good Friday in 1964 fell on 27th March.
The people of Alaska awoke to a normal cold Bank Holiday, and it continued that way as far as anyone could tell, until 5.36pm local time (3.36 on 27th March UTC.)
At that time, some 14 miles below Prince William Sound, approximately 80 miles east of Anchorage, near College Fjiord, the Pacific Plate and the North American Plate fractured with magnitude on the Richter Scale of 8.5 and a Moment Magnitude of 9.2 [1] with the epicentre at 61.1N 147.5W.
It started with about 10 seconds of rumbling and slight movement. The Alaskan people were very used to this and really took little notice.
Then the ground started to ripple and heave with surface waves and fissures up to 30' wide opened and closed. Glass fractured in building before the buildings themselves started to break up.
This main quake lasted four and a half minutes. It triggered landslides and avalanches, which in turn set off tsunamis; it brought down buildings and tore up roads. Bridges collapsed and beaches were raised. The rail freight yard was completely demolished.
Liquefaction[2] was the cause of many of the building in Anchorage collapsing, the shaking disturbing the sands and clay lenses below, causing their strength to drop below the stability level.
The fracture tilted an area of Alaska the size of Wales, drowning forests at one end and leaving ships grounded far from the sea at the other. Areas east of Kodiak were raised up to 30', with the town of Portage dropping over 8'. The following winter ice flows were reported floating down the main street of that town.
The greater part of the 139 deaths was due to the tsunamis which were generated by tectonic uplift of the bed of Prince William Sound, and by sub-areal and submarine landslides. The shaking caused five slide generated tsunamis within minutes after it began. These five occurred at Kachemak Bay, Seward, Whittier, and two at Valdez.
As an example and in brief summary: In Seward, a section of just over one kilometre of the water front slid into the Resurrection Bay due to the earthquake shaking. This created a local tsunami causing a great deal of damage and spread oil from fractured tanks which caught fire and floated on the water. About 20 minutes after this occurred, the first wave of the main tsunami arrived.
The number of tsunamis does not seem to be recorded, but it is recorded that they went on until 2 a.m. local time.
The damage was not confined to Alaska. There was earthquake damage right across the Aleutian Islands, and probably into the coastal regions of the Kamchatka Peninsular but this was the height of the Cold War, so the Soviet Union did not report it to the outside world. Those places were also hit with the tsunamis.
The shock was felt badly in Vancouver Island, Canada and Depoe, Oregon, and tremors were even felt in California. All these place were affected by the tsunami which even reached Hawai'i and Japan.
Without belittling 139 deaths it must be considered very fortunate that this was a very unpopulated area. Had it happened almost anywhere else around the Pacific Rim the loss of life might have been as catastrophic as we saw in The Anderman Islands and Indian Ocean on Boxing Day 2004.
The main severe after-shocks continued for three days, and overall it took 18 months to settle into quietness again after over 10,000
minor shocks.
1. Moment magnitude scale
From Wikipedia, the free encyclopedia
The moment magnitude scale (abbreviated as MMS; denoted as MW or M) is used by seismologists to measure the size of earthquakes in terms of the energy released.[1] The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped.[2] The scale was developed in the 1970s to succeed the 1930s-era Richter magnitude scale (ML). Even though the formulae are different, the new scale retains the familiar continuum of magnitude values defined by the older one. The MMS is now the scale used to estimate magnitudes for all modern large earthquakes by the United States Geological Survey.[3]
2. Liquefraction
From Wikipedia, the free encyclopedia
In geology, soil liquefaction refers to the process by which water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid, often in an earthquake. By undermining the foundations and base courses of infrastructure, liquefaction can cause serious damage.
N.B. For pictures of the damage, Google 'images' of 'Good Friday 1964 Alaskan earthquake' .
John.
John
“Civilisation exists by geological consent, subject to change without notice.” - Will Durant