Lecture2-seismic Methods And Engineering Flashcards
(15 cards)
What is seismology used for?
To determine the direction from which waves originated.
What do slow waves and fast waves tell us about the soil?
Slow waves → soft soil, loose sediments
Fast waves → solid rock, strong foundation.
What happens when seismic waves reach an underground boundary?
They can be refracted at a critical angle only if the deeper layer has a higher velocity.
What influences the speed of waves?
Elastic properties of the medium through which they propagate.
What are elastic moduli?
Set of constants that define the properties of a material.
What is stress and strain?
Stress is a force that is applied on an object.
Strain is the distortion/deformation caused by stress.
What is stress and strain on an object dependent on?
The strength and direction of stress, and properties of the object.
What is Bulk modulus?
A measure of how resistant to compression an object is.
What is Shear modulus?
Ratio of shear stress to shear strain.
What is Young’s modulus?
A solid material will undergo elastic deformation when a small force is applied to it in compression/extension.
Where do surface waves originate from?
Interaction of P and S waves in the Earth.
What are surface wave velocities?
Each surface wave contains a range of frequencies at a different velocity.
Surface wave vs. sensitivity?
Each frequency is sensitive to a certain depth.
Shorter periods/higher frequency → shallower depth.
Longer periods/lower frequency → larger depth.
What is crossover distance in seismology?
Marks the seismic wave journey: Interface A & B.
What is Poisson’s Ratio (ν)?
Shows that change in diameter (d1-d2) is proportional to change in length. It governs the speed at which a wave travels through a material.
