Categorized | Sci-Tech

Volcano Watch: Earthquakes provide warnings of activity

An HVO scientist and volunteer work to upgrade the power system of a seismic station located in the Ka‘u desert on Kilauea’s southwest rift zone.  USGS Photo.

An HVO scientist and volunteer work to upgrade the power system of a seismic station located in the Ka‘u desert on Kilauea’s southwest rift zone. USGS Photo.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

This week, we continue our series of Volcano Watch articles on volcano monitoring with a discussion of seismic techniques.

Seismic monitoring is perhaps the most commonly used and well-known method for tracking volcanic activity — and for good reason. The very movement of magma beneath the surface causes earthquakes, both due to breaking of rock from magma pressure and from the fluid motion itself.

Tracking the number, magnitude, depth, and type of earthquakes at a volcano provides an indication of where magma is located and whether or not it is rising toward the surface.

While simple in concept, however, volcano seismology is much more complicated in practice. For example, earthquakes associated with volcanic activity come in many different styles, depending on the characteristics of the earthquake waves.

Volcano-tectonic (VT) earthquakes have high rates of shaking, while long-period (LP) and very-long period (VLP) earthquakes have lower rates of shaking. These earthquake types are analogous to sound waves.

Very short-period acoustic waves, like chaotic radio static, are like VT earthquakes, whereas the longer-period oscillations in pitch produced by a fire engine’s siren exemplify LP and VLP earthquakes.

VT, LP, and VLP earthquakes also suggest different sources. VT seismicity is often associated with breaking rock, which might occur at the front of a propagating magmatic intrusion. In contrast, LP and VLP earthquakes are thought to reflect fluid oscillations in subsurface magma and gas.

In addition to discrete earthquakes, volcanoes also produce continuous, low-level seismic tremor, which can be considered the background noise of a volcano. Tremor tends to increase before an eruption and decrease during periods of no eruption and is, therefore, a useful indicator of the level of activity of a given volcano.

Locating tremor and earthquake sources is critical for mapping a volcano’s magma plumbing system and assessing volcanic activity. For example, tremor, LP, and VLP earthquakes have been used to map magma storage areas beneath Kilauea’s summit, while migration of VT events is commonly used to track magma migration along Kilauea’s east rift zone, and even magma ascent prior to eruptions.

A network of seismometers capable of measuring very small levels of ground motion is required to locate an earthquake. Like earthquakes themselves, seismometers come in many varieties, each of which is sensitive to different types of ground shaking. Short-period seismometers are the least expensive and are excellent at detecting VT earthquakes. Broadband seismometers are more expensive but can detect LP and VLP earthquakes.

Kilauea and Mauna Loa were the first volcanoes in the United States to be monitored by a modern seismic network, which was installed in the 1950s and continues to be expanded today. Thanks to funding from the American Recovery and Reinvestment Act (ARRA), HVO’s seismometers are currently being upgraded to all digital instruments with a mix of short-period and broadband sensors.

Using the wealth of seismic data recorded by HVO, seismologists have learned much about the structure of Hawai`i’s volcanoes. For example, a persistent source of VLP and LP earthquakes and tremor occurs about 1 km (0.6 mi) beneath Kilauea’s summit, indicating the presence of a shallow magma reservoir.

Next week, in the final part of our series on volcano monitoring methods, we will describe how volcanologists use motion of the Earth’s surface to assess where magma is located beneath the ground and whether or not it is likely to erupt.

Until then, you may want to attend some of this week’s Volcano Awareness Month activities, which include a presentation about the 1911 observations of Kilauea by volcanologist Frank Perret in the Hawaii Volcanoes National Park Visitor Center on Jan. 25; a talk about volcanic gas emissions and vog at the Konawaena High School cafeteria on Jan. 27; a talk about the link between volcanoes and early Hawaiian stone tools at the University of Hawaii at Hilo on Jan. 28, and daily National Park programs.

Details about these and other Volcano Awareness Month activities is available at http://hvo.wr.usgs.gov or by calling 808-967-8844.

5 Responses to “Volcano Watch: Earthquakes provide warnings of activity”

  1. john delano says:

    People are wrong about Hawaii and its formation.

  2. john delano says:

    Hawaii is at the end of the 3,000 mile long “Emperor Seamounts”, and where the seamounts have “popped” there heads above sea-level the lava has hardened and “can be tested for its age based on the “hardening of the lava.
    Scientists “picked” a 20 million years old Island and a 10 million years old Island and “made the claim that these Islands traveled over a”hot Spot” in the earths lithosphere, a “Plume” of molten magma the has risen from the hot core of the center of the earth.

    The picking of those island was not random and the scientist “forced” the “moveing over the hot spot theory.”
    They “fudged” the answer.
    Read on if you want proof.
    sunnyday1@optonline.net
    john delano

  3. john delano says:

    “Why did the scientist fudge the Hawii hot spot theory?”
    What does the hardening of islands made of lava have to do with moving?
    let me ask you this question so that you can understand what I am saying.
    Your mother cooks 3 apple pies- one [1] is the very large 16 inch deepdish kind, one is the 9 inch standard pie, and one is those small apple pies you eat in 5 bites, you know the 3 inch pie.
    Mom places the 3 pies cooked in three separate ovens ,all ozzing apple jucies on the window sill to cool.
    After 10 minutes [notice the correlation with the 10 million year old island]the 3 inch pie can be eaten, but the 9 and 16 inch pies are still ozzing.
    After 20 minutes the 9 inch pie has cooled and it has stopped ozzing; [notice the freference to the 20 million years old Island in the example]

    The 16 inch deep dish pie is still ozzing apple juices, and can not be eated.

    My question to you is this .
    How far has the large 16 inch deep dish apple pie moved from the 3 inch pie and the 9 inch pie???????????????

    The pies did not move, and neither did thos Islands move over a ficteous “hot spot.”

    Read on.
    john Delano.

  4. john delano says:

    Hawaii like the 16 inch deep dish apple pie has a massive volume of material , ans is taking along time to cool.
    the Magma pool under “Hawaii” is huge and must go down 500 miles or more.
    Hawaii was formed in the middle of the Pacific Ocean because it is a crustal “pivot point” on Planet Earth. Opposite Hawaii [antipodal] is the other pivot point on the globe -Botswana South Africa.

    The pacific ocean before it was an ocean was the “Pacific hollow”, an excavation caused by the moon-forming collision 4.5 billion years ago.
    to be continued…

  5. Huh? says:

    You sir, are a wacko.

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