Lecture 1 - Seismics A

Question 1

What is a seismic wave?

Answer 1

An acoustic energy transmitted by the vibration of rock particles

Question 2

What effect do low energy waves have on rocks?

Answer 2

None, waves are elastic and leave the rock undisturbed

Question 3

Name 3 sources of seismic waves

Answer 3

Natural source (e.g. earthquake), explosive source (e.g. bomb) or a heavy impact (e.g. hammer)

Question 4

In what ways is it possible to record seismic waves?

Answer 4

Seismograph, geophone or a hydrophone (oceans)

Question 5

What direction do seismic waves radiate?

Answer 5

In all directions

Question 6

Describe the path taken by a reflected p-wave

Answer 6

Reflected p-waves radiate down at an angle, upon reaching the interface between a new layer of rocks it gets reflected back to the surface where it can be detected by geophones. Reflected waves reach further away geophones later.

Question 7

Describe the path taken by refracted p-waves

Answer 7

Refracted p-waves hit the lower interface and travel along it throwing energy back to surface through diffraction.

Question 8

Describe the path of a direct p-wave

Answer 8

Direct p-waves travel along surface straight from shot point to detector

Question 9

Which waves are detected by detectors first?

Answer 9

Direct waves

Question 10

Which waves are not detected by the first set of geophones?

Answer 10

Refreacted waves

Question 11

How can we work out seismic velocity in the top layer of a graph of p-waves?

Answer 11

\the gradient of the straight line

Question 12

How can we find out the depth of the interface?

Answer 12

The time that it takes for the reflected waves to get to the surface