Earthquake Articles - Facts - Videos

Earthquake Facts - Videos

EARTHQUAKE ARTICLES - NASA

1964 ALASKAN EARTHQUAKE

The earthquake was accompanied by vertical displacement over an area of about 520,000 square kilometers. The major area of uplift trended northeast from southern Kodiak Island to Prince William Sound and trended east-west to the east of the sound. Vertical displacements ranged from about 11.5 meters of uplift to 2.3 meters of subsidence relative to sea level. Off the southwest end of Montague Island, there was absolute vertical displacement of about 13 - 15 meters. Uplift also occurred along the extreme southeast coast of Kodiak Island, Sitkalidak Island, and over part or all of Sitkinak Island. This zone of subsidence covered about 285,000 square kilometers, including the north and west parts of Prince William Sound, the west part of the Chugach Mountains, most of Kenai Peninsula, and almost all the Kodiak Island group.

This shock generated a tsunami that devastated many towns along the Gulf of Alaska, and left serious damage at Alberni and Port Alberni, Canada, along the West Coast of the United States (15 killed), and in Hawaii. The maximum wave height recorded was 67 meters at Valdez Inlet. Seiche action in rivers, lakes, bayous, and protected harbors and waterways along the Gulf Coast of Louisiana and Texas caused minor damage. It was also recorded on tide gages in Cuba and Puerto Rico.

This great earthquake was felt over a large area of Alaska and in parts of western Yukon Territory and British Columbia, Canada.[1]

The area where there was significant damage covered about 130,000 square kilometers. The area in which it was felt was about 1,300,000 square kilometers (all of Alaska, parts of Canada, and south to Washington). The four minute duration of shaking triggered many landslides and avalanches. Major structural damage occurred in many of the major cities in Alaska. The damage totalled 300-400 million dollars (1964 dollars)…

Of the 119 deaths attributable to the effects of the ocean, about one-third were due to the open-ocean tsunami: 4 at Newport Beach, Oregon; 12 at Crescent City, California; and about 21 in Alaska. Local waves claimed at least 82 lives.[2]

[1] “Historic Earthquakes: Prince William Sound, Alaska: 1964 March 28.” U.S. Geological Survey. Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.  Retrieved August 30, 2011.

[2] Christensen, Doug. “The Great Alaska Earthquake of 1964.” November 2002. Retrieved August 30, 2011.



Much more information is available on the Internet:

RAT ISLANDS

The Rat Islands are part of the Aleutian Islands off of Alaska. According to the Alaska Earthquake Information Center, “Large earthquakes in the Aleutian arc occur on the convergent boundary between the Pacific and North American crustal plates. This region, where the two plates are being forced directly into one another, is one of the world’s most active seismic zones. Over one hundred earthquakes of magnitude seven or larger have occurred along this boundary in the past hundred years.”[1]

[1] Ratchkovski, N. “February 4, 1965 Rat Islands Earthquake.” May 2005. Alaska Earthquake Information Center (AEIC). Retrieved September 1, 2011. http://www.aeic.alaska.edu/quakes/rat_islands_1965.html

EARTHQUAKE MEASUREMENTS

The Richter scale is the one most commonly referred to. For mathematical reasons, Richter is accurate only up to about 6.5. For larger quakes, scientists use the newer moment magnitude scale.[1]

There are several ways to measure an earthquake, but the most common is magnitude. Scientists no longer use the original Richter scale, but an updated version. Earthquakes should be referred to as “magnitude X” rather than “an X on the Richter scale.” A magnitude 6.0 earthquake releases 32 times more energy than a magnitude 5.0 and nearly 1,000 times more energy than a 4.0. But that doesn't mean the ground shakes a thousand times harder in a 6.0 than a 4.0, because the energy is released over a much larger area.

How much power does an earthquake pack? A magnitude 6.0 quake releases approximately as much energy as 6,270 tons of TNT, an M 7.0 199,000 tons, an M 8.0 6.27 million tons and a M 9.0 99 million tons. Of course, all that energy is not focused in one particular spot, but spreads out in waves.[2]

[1] “Quake Basics—Measurements.” Faultine: Seismic Science at the Epicenter. Retrieved August 30, 2011.

[2] “Earthquakes – A Whole Lotta Shakin’ Goin’ On.” State of California – Department of Conservation. Retrieved September 29, 2011.

EARTHQUAKES - INFORMATIVE WEBSITES

Many websites contain information about earthquakes, of which these are a few. 

HOW MUCH POWER DOES AN EARTHQUAKE PACK?

  • A magnitude 6.0 quake releases approximately as much energy as 6,270 tons of TNT,
  • an M 7.0 199,000 tons,
  • an M 8.0 6.27 million tons
  • and a M 9.0 99 million tons.
  • Of course, all that energy is not focused in one particular spot, but spreads out in waves.

WHAT FACTORS INFLUENCE WHAT YOU FEEL IN AN EARTHQUAKE?

There are three major factors: magnitude, your distance from the fault, and local soil conditions. 
  • Magnitude is discussed above.  
  • As for distance, the seismic waves that cause the shaking become less intense farther from the fault.  
  • Certain soil conditions amplify the shaking; generally, the looser the soil, the greater the amplification.  
Although most of San Francisco escaped serious damage in Loma Prieta, those with unconsolidated landfill or soft soils (such as the Marina District) suffered serious damage. The ground motion in such areas was 10 times stronger than at neighboring sites on rock. 

WHAT IS A FAULT?

  • A fault is a fracture in the crust along which one side has moved relative to the other side. Faults can be very small or hundreds of miles long.
  • The earth's crust is composed of huge plates that are in slow but nearly constant motion.
  • Part of California is on the Pacific Plate, and part is on the North American Plate. The San Andreas Fault, which runs from the Salton Sea in Imperial County to Cape Mendocino in Humboldt County, is the boundary between these plates.
  • Sometimes one block of the crust moves up while the other moves down, sometimes they move horizontally in opposite directions (that's what's happening with the San Andreas Fault; Los Angeles is creeping closer to San Francisco).
  • Some faults are well known and easy to spot, such as the San Andreas. Others are underground, with nothing on the surface revealing their presence (a blind thrust fault). The 1994 Northridge earthquake was caused by a blind thrust fault.

HOW COMMON ARE FAULTS IN CALIFORNIA?

  • There are hundreds of identified faults in California; about 200 are considered potentially hazardous based on their slip rates in recent geological time (the last 10,000 years). 
  • More than 70 percent of the state's population resides within 30 miles of a fault where high ground shaking could occur in the next 50 years.

EARTHQUAKE PREPAREDNESS

Many websites and groups offer information on earthquake preparedness. Below are a few:

EARTHQUAKE - YOU-TUBE VIDEOS

  • This video shows the buildings swaying during the earthquake in Japan on March 11, 2011.

EARTHQUAKE - JAPAN - 3-11-2011

LIQUEFACTION - DEFINED

When loosely packed and wet sand is shaken during an earthquake, it may flow like liquid. This is called liquefaction. Anyone who has walked on a beach may have seen a small-scale version of this process. Stamp your foot in the sand near the water’s edge and suddenly the area of your footprint vibrates like gelatin.

Earthquake-induced liquefaction is often accompanied by cracks in the ground surface and small eruptions of sand and water called sand blows. During the 2002 Denali Fault earthquake, people in Northway watched sand erupting 4 feet out of the ground. When a soil liquefies, it is unable to support the weight of the ground or any structures above it. Bridges and buildings may settle and tilt even though they withstood strong ground shaking. If the liquefied area is on a slope, massive landslides may result.

The Bootlegger Cove Formation is the name of a soil that underlies much of Anchorage. Liquefaction of a part of the Bootlegger Cove Formation caused much of the destruction in the Anchorage area during the 1964 earthquake, and it causes people to feel earthquakes more strongly in western Anchorage. Soils that liquefy are not limited to the Anchorage area, but are present in many low-lying parts of Alaska where soil near the surface is saturated with water.

LIQUEFACTION - INFORMATIVE WEBSITES

LIQUEFACTION - YOU-TUBE VIDEOS

  • After a series of earthquakes, a person did this video to help explain to friends what liquefaction is and how it occurred during the earthquakes in Christchurch, New Zealand. (uploaded 2-26-2011)

LIQUEFACTION - Demonstration - Christchurch

  • This video was taken just moments after the 9.0 earthquake on March 11, 2011 in Central Park of Makuhari, Chiba City, Japan. It shows fissures moving and water from liquefaction coming to the surface.

LIQUEFACTION - JAPAN - 3-2011 - Video 1

  • This video was taken after the earthquake in Japan. 

LIQUEFACTION - JAPAN - 3-2011 - Video 2

WHAT IS A TSUNAMI?

  • Sometimes called seismic sea waves (or, incorrectly, tidal waves), a tsunami is a series of waves generated by large earthquakes that create vertical movement on the ocean floor.
  • Tsunamis can reach more than 50 feet in height, move inland several hundred feet and threaten life and property.
  • Often, the first wave of a tsunami is not the largest.
  • Tsunamis can occur on all coastal regions of the world, but are most common along margins of the Pacific Ocean.
  • Tsunamis can travel from one side of the Pacific to the other in a day, at a velocity of 600 miles an hour in deep water.
  • A locally generated tsunami may reach the shore within minutes.

WHAT IS A TSUNAMI? - Poster

TSUNAMI - YOUTUBE VIDEOS

  • Tsunami waves coming in. Japan on March 11, 2011. This video shows a tsunami wave smashing into the Japanese town of Miyako, in Iwate Prefecture. The wave crashes over the seawall carrying away everything in its path, including boats that topple over the wall and are smashed into a bridge. Cars were simply washed away, crashing into each other and buildings.

TSUNAMI - JAPAN - 3-2011 - Video 1

  • Tsunami wave coming into Minami-Sanriku. Japan on March 11, 2011.

TSUNAMI - JAPAN - 3-2011 - Video 2

  • Tsunami wave battering ships, etc. Japan on March 11, 2011.

TSUNAMI - JAPAN - 3-2011 - Video 3

  • Tsunami wave coming through town. Japan on March 11, 2011.

TSUNAMI - JAPAN - 3-2011 - Video 4

  • Aerial view from a helicopter of tsunami. Japan on March 11, 2011.

TSUNAMI - JAPAN - 3-2011 - Video 5

OTHER INFORMATIVE WEBSITES