Earthquakes of the 20th Century

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    Animation from NWS Pacific Tsunami Warning Center shows earthquakes of the 20th century.


    This animation shows every recorded earthquake in sequence as they occurred from January 1, 1901, through December 31, 2000, at a rate of 1 year per second. The earthquake hypocenters first appear as flashes then remain as colored circles before shrinking with time so as not to obscure subsequent earthquakes. The size of the circle represents the earthquake magnitude while the color represents its depth within the earth. At the end of the animation it will first show all quakes in this 100-year period. Next, it will show only those earthquakes greater than magnitude 6.5, the smallest earthquake size known to make a tsunami. It will then show only those earthquakes with magnitudes of 8.0 or larger, the “great” earthquakes most likely to pose a tsunami threat when they occur under the ocean or near a coastline and when they are shallow within the earth (less than 100 km or 60 mi. deep). The animation concludes by showing the plate boundary faults responsible for the majority of all of these earthquakes.

    The era of modern earthquake seismology—the scientific study of earthquakes—began in the 20th Century with the invention of the seismometer and its deployment in instrument networks to record and measure earthquakes as they occur. Therefore, when the animation begins only the largest earthquakes appear as they were the only ones that could be detected at great distances with the few available instruments available at the time. But as time progresses, more and more seismometers were deployed and smaller and smaller earthquakes could be recorded. For example, note how in the 1930’s many small earthquakes suddenly seem to appear in California, but this illusion results from the installation of more and more instruments in that region. Likewise, there appears to be a jump in the number of earthquakes globally in the 1970’s when seismology took another leap forward with advances in telecommunications and signal processing with digital computers, a trend that continues today.

    20th Century seismology revealed the global geographic distribution of earthquakes and helped to solidify the Theory of Plate Tectonics. Notice how earthquake epicenters do not occur randomly in space but form patterns over the earth’s surface, revealing the boundaries between tectonic plates as shown toward the end of this animation. This time period also includes some remarkable events, including those that generated devastating tsunamis:

    8.8 — Ecuador — 31January 1906
    8.4 — Kamchatka, Russia — 3 February 1923
    8.4 — Sanriku, Japan — 2 March 1933
    8.6 — Unimak Island, Aleutian Islands — 1 April 1946
    9.0 — Kamchatka, Russia — 4 November 1952
    8.6 — Andreanof Islands, Aleutian Islands — 9 March 1957
    9.5 — Valdivia, Chile — 22 May 1960
    9.2 — Prince William Sound, Alaska — 28 March 1964
    8.7 — Rat Islands, Aleutian Islands — 4 February 1965

    These earthquakes represent some of the largest ever recorded. Note how they all occur at a particular type of plate boundary, subduction zones where tectonic plates collide, so these are the regions where we expect future devastating tsunamis to be generated.

  • Also, take a look at the Smithsonian's Eruptions, Earthquakes, & Emissions player/viewer as well, to help complete the picture of active geological activity on Earth.

    "The Smithsonian's "Eruptions, Earthquakes, & Emissions" web application (or "E3") is a time-lapse animation of volcanic eruptions and earthquakes since 1960. It also shows volcanic gas emissions (sulfur dioxide, SO2) since 1978 — the first year satellites were available to provide global monitoring of SO2. The eruption data are drawn from the Volcanoes of the World (VOTW) database maintained by the Smithsonian's Global Volcanism Program (GVP). The earthquake data are pulled from the United States Geological Survey (USGS) Earthquake Catalog. Sulfur-dioxide emissions data incorporated into the VOTW for use here originate in NASA's Multi-Satellite Volcanic Sulfur Dioxide L4 Long-Term Global Database."


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    Eruptions, Earthquakes, & Emissions player/viewer is here:

    Windy provides forecasts of global emission of such sulfur dioxide (SO2) gases, from both geological and human sources.

    Precipitation of solid sulfur from a vent of volcanic water and gas, called a fumarole:

    Mining of sulfur (Freeport Sulphur Co., Hoskins Mound, Texas in 1943).

    Natural 'massive' sulfur mineral precipitate, deposited from evaporated water that contained a lot of dissolved sulfur in it:

    Jupiter's moon Io is completely covered in volcanic emissions and resulting yellow sulfur deposits, which are constantly changing as the moon is continuously resurfaced with every new major eruption (which are almost constant):
    Images from Wikipedia public imagery sources.

    Thus sulfur, in the form of atmospheric SO2, is a natural part of the planet's atmosphere and also its crustal mineralogy. But it's also produced as a component of human industrial processes. It can become a locally intense plus also a regionally diffuse chronic pollutant. Especially in and from China due to China's extremely poor and even dangerous air quality within cities and industrial areas. This occurs mainly due to China's almost non-existent SO2 emission control, or else a lack of enforcement of pollution emissions standards within China. Many major Russian cities and industrial sites are also almost as bad, but not as concentrated in areas affected, compared to China.

    SO2 gas emissions forecast in China tomorrow, on Windy:

    Screenshot_2019-04-11 Windy as forecasted.png

    Natural sulfur dioxide SO2 gas emissions constantly occur from chains of hundreds of volcanoes all around the Pacific ocean basin's rim.

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    Windy's SO2 display,39.368,150.381,4,p:off

    Such sulfur emission also occurs underwater from millions of hot hydrothermal springs and 'black smoker' metal sulfide 'chimney' structures. Most of earth's copious SO2 sulfur emission ends up in ocean waters and oceanic sediments. In fact natural sulfuric acid is a component of volcanic and hydrothermal emissions into the ocean and atmosphere.


    Image sources:

    Major volcanic eruptions also produce extremely intense emissions of SO2 that can be punched high into Earth's upper atmosphere. So much so that it can produce vivid salmon-pink sunsets due to SO2 which was launched high into the stratosphere, where it stays for a year or so before dissipating. The reflection of light from this SO2 alters the Earth's albedo (external sunlight reflectivity brightness of the planet, when viewed from space):

    A twilight sky can be colored pink via light scattered from volcanic eruptions of copious SO2 gas injected into the stratosphere - from the Calbuco volcano's eruptions, in this case.




    Creation of sulfuric acid in the atmosphere from SO2:

    Screenshot_2019-04-11 Sulfuric acid - Wikipedia.png




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