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What Is Seismic Reflection?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 13 November 2014
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Seismic reflection is a principle which is utilized in geology to gather information about what is going on underneath the surface of the Earth. Sound waves underground are subject to the same physical principles which govern the travel of energy above ground, and with these principles in mind, geologists can use the movement of sound waves underground to generate data about subsurface geological formations. A closely related concept is seismic refraction, which involves the study of the ways in which sound waves bend as they encounter obstacles underground.

For a seismic reflection survey, geologists need something to generate noise, such as a large vibrating device, a controlled explosion, or a heavy object which can be dropped to create a sound wave. They also need geophones, sensitive listening devices which can be placed on the surface of the Earth to listen for the sound waves as they return. A field team operates the devices, collects the data, and makes observations about the setting of the seismic reflection study, taking note of anything which could skew results.

As the soundwaves move underground, some are reflected back up to the surface of the Earth, where they are picked up by the geophones. Using geophone data, researchers can create a plot which reveals the outline of formations and objects in the ground. In a way, seismic reflection works sort of like ultrasound and radar, with people generating soundwaves and listening for their return to get information about something they cannot see.

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For a seismic reflection study to work well, the area being surveyed generally needs to be deep. If it is too shallow, the reflected sound waves can bunch together, making it hard to differentiate between the waves and muddying the results. It also helps to have multiple geophones to listen from several different angles. Refraction studies, on the other hand, are capable of being used in shallower ground, but they have some limitations, such as difficulty when surveying involves materials of high density overlayed on materials of lower density.

The principles behind seismic reflection studies are also used in the study of earthquakes, except that because the researchers do not know where the source of the energy is located, they need to be able to use input from multiple seismographs to narrow in on the epicenter. This is done by plugging the data into an equation, using an understanding of how energy moves through the Earth to determine where the energy is coming from.

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Mammmood
Post 2

@everetra - It may not be totally wishful thinking. Seismic reflection appears to be an ongoing study of what the Earth is doing, well before any earthquake takes place.

Perhaps with this information the scientists can in fact sound warning bells of potential earthquakes before they happen.

I realize they haven’t been that successful in predicting, but at least pointing to where substantial activity is happening would be a start.

everetra
Post 1

I remember during the big Indonesian tsunami of 2004 that there were many oceanographers who were able to use seismic data acquisition to collect important information about the scope of the earthquake.

I saw lined plots based off this data that revealed the outline of the underlying geological formations and the dramatic changes that took place. Superimposed against the photographs of the affected locations, I thought it was very instructive – not to mention, terribly sad.

I would hope that seismic data acquisition used in this way would not only be useful in describing the shape of the events underneath the Earth, but would enable scientists to somehow predict where such things might take place in the future.

That might be a little wishful thinking on my part, but that would be the best use of this technology in my opinion.

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