Taking a Picture of the Earth Deep Beneath Our Feet
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| Figure 1 | Poor image quality -Little information is given to aid in the understanding of this image. |
The figure to the right (Figure1) may look a bit incomprehensible. Even through you have
more information in some locations than others, regarding the shapes and colors, it may still be puzzling to figure out what is going on in this image. The poor image quality leaves much room for
interpretation, if we want a better idea of what Figure 1 is we will need more
information for higher resolution.
In
the past, lack of information to create higher resolution images has been a problem in
creating seismologists’ picture of the continents. Seismologists seek to reveal the geologic
structure (the type and thickness of differing rock layers) many kilometers
beneath our feet. Seismologists look into the earth with seismograms collected
from seismic stations. Seismograms contain information about four main things:
an earthquake, the station, background movement, and the geologic structure of
the earth. If we remove the earthquake, station, and background information, we
are left with information from the earth’s structure. This is one method
seismologists use to “see” a little bit of the earth’s structure at each
station. The effect is similar to a taking a telescope and pointing it into the
ground at each station. Until recently, the images of the geologic structure from seismic stations have been fairly unclear (like Figure 1). The National
Science Foundation funded project to improve the image (or resolution) of the
interior of the earth called Earthscope
USArray.
Earthscope USArray densely packed seismic stations across the
continental US and Alaska to collect information about the earth beneath our
feet. The increased station coverage (Figure 2) allows us to gather more
information and create a higher resolution image of the geologic structure. The
idea is similar to increasing the resolution of an image. If we look at Figure
3, we see the higher resolution image of Figure 1. Now that we have more
information we can better understand what’s going on in the picture, just like understanding
the continent with Earthscope USArray.
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| Figure 2 | Left: Earthscope USArray station coverage Right: Prior Station coverage |
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| Figure 3 | Left: improved image of Figure 1with more information (Now we can see the image was grumpy cat) Right: Poor image quality with little information. |
The dense seismic stations provide the highest
resolution image of any continent, allowing scientists to look at the earth in
a whole new way. The vast majority of the human population lives on a
continent. In fact, you are likely on one right now. It may be surprising to
find then, that we know very little about the structure within these continents.
In fact, scientists have found a layer present in almost all continents 100
kilometers (km) beneath our feet that has not been able to be explained –we
don’t know why it is there or what the consequences of this layer have been. Some have suggested that this layer may be
related to the locations of large earthquakes that occur in the middle of the continents. In the
United States most earthquakes are located on the west coast, however if we look
at locations of some of the largest earthquakes and earthquake hazard areas in
Figure 4, you will find bright red areas associated with high hazard in the St.
Louis, MO area. If there is a correlation between some characteristic of the
100km layer within the continents and the high hazard areas within continents
of the US, we may be able to where other large earthquakes in continents may
occur. Even if no correlation exists, this layer might preserve billion year
old secrets to continental formation, alteration, and breakup and provide
insight to the past, present, and future of our continent.
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| Figure 4 | Hazard map from United States Geological Survey. Areas with high seismic hazard are in warmer colors with red being the most hazardous, while cooler colors indicate low seismic hazard with dark blue being the least hazardous. |
For more information about Earthscope and projects being done, visit:
To make your own earthquake map (like Figure 4) visit:
USGS Earthquake Hazard Program - http://earthquake.usgs.gov/earthquakes/search/
References:
References:
"Earthquake Hazards Program." Earthquake Hazards Program. US Department of the Interior - United States Geological Society, 26.Aug, 2014.
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