Seismic Methods (refraction methods and processing)

Question 1

What is the principle of seismic surveying?

Answer 1

Investigation of elastic waves (also called seismic waves) that travel with different velocities in different rocks.

Question 2

What can be observed and determined through the generation of a seismic waves?

Answer 2

the times of arrival at a certain fixed detector point (geophones) placed on the ground surface
– can be determined the subground velocity distribution

Question 3

How is seismology classified depending on the energy source involved in the travelling of seismic waves?

Answer 3

• earthquake seismology (global earth scale)
• explosion seismology (refraction and reflection)

Question 4

What is earthquake seismology?

Answer 4

investigation and information (physical properties and structure) from earth’s interior (Earth/Global/Pure Geophysics)
- In context of: studies of earthquake (magnitude and frequency), seismic hazards and earthquake science

Question 5

What is explosion seismology?

Answer 5

investigation and information (physical properties and structure) from earth’s crust and application on environment and geotechnical problem (applied geo-seismic and thus applied Geophysics)

Question 6

What are the main laws and principles regulating the seismic methods?

Answer 6

• Elastic Waves (i.e. theory of elasticity, Hooke’s Law)
• Snell’s Law
• Huygen’s Law
• Fermat Principle

Question 7

What are the types of elastic waves?

Answer 7

• body waves (Primary-waves, Secondary-waves)
• surface waves (Rayleigh waves, Love waves)

Question 8

What is Huygens principle?

Answer 8

“Every single point on a wavefront can be considered to be a secondary source of spherical waves travelling radially outward that source point” thus
the new wavefront is the envelope of these waves after given time interval (i.e. the tangential surface)

Question 9

What does Huygens principle (Diffraction) state in specific?

Answer 9

• each point on a wavefront generates secondary wavelets
• these wavelets interfere with each other, causing waves to bend or spread as they pass through slits or around obstacles
• diffraction patterns result from the constructive and destructive interference of these wavelets

Question 10

What is Snell’s Law?

Answer 10

When an elastic wave encounters and interface between materials of different elastic properties, energy is partly reflected and partly transmitted (refracted) in second media.
The angle of incidence equals the angle of reflection, and the angle of transmission is related to the angle of incidence through the velocity ratio.