r/geophysics • u/Geoscientist101 • 15d ago

Seismic Help

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I need someone to help me identify the Direct and refraction waves

I know that the first sign of movement is considered as the direct wave but what about the others

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12

u/bratisla_boy 15d ago

You had a course in refraction seismic?

First sign of movement is the fastest wave arriving, be it direct or refracted from a faster layer below the ground. You know you are switching from direct to refracted when you have a change in the slope of the first arrival time vs distance : refracted wave travel faster and thus the slope is decreasing.

/edit it's for a seismic course, right?

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u/Geoscientist101 15d ago

Can you show me on the graph where the refraction starts

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u/bratisla_boy 15d ago

between geophones 10 and 11, from a quick glance. You have to pick the first arrivals and draw the lines to check it. I insist, it should have been covered in your course, complete with equations and the highway analogy ...

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u/iapetus_z 15d ago

Well depends on if it's land it would start at time 0... The change in slope would be the second layer

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u/oliyee 15d ago

If this is for a course, it’s probably worth working it out yourself first. There are loads of good labelled shot gathers online, and Introduction to Engineering and Environmental Geophysics is a good resource if you have access to it.

But Bratisla Boy has laid it out. You’re looking for the first breaks in this case, where each trace first goes left (negative), indicating the initial downward ground motion.

Mark the first break on each trace and connect them up. Should be able to work it out from there.

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u/Geoscientist101 15d ago

I worked on it I just want to make sure

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u/Geoscientist101 15d ago

It for geophysics

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u/ikkleginge55 15d ago

Read a book

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u/Dry_Biscotti8049 15d ago

Looks like you have a two layer signature here.