GEO ENCN454 Flashcards
(43 cards)
1
Q
Hypocentre
A
- The location where the earthquake fault rupture starts, below the surface
2
Q
Epicenter
A
- Is the projection of the hypocenter onto the ground surface
3
Q
Seismic waves consist of…
A
- Body waves
> P-waves
> S-Waves - SV waves, SH waves
- Surface Waves
> Rayleighs waves
> Love Waves
3
Q
Seismic waves consist of…
A
- Body waves
> P-waves
> S-Waves
4
Q
Body waves
A
Travel within body of the earth
- P waves
- S waves
5
Q
P-waves
A
- Compressional waves
- Motion of individual particle in direction of wave motion
- Produces successive compression and dilation deformations
- Can travel through solids and fluids`
6
Q
S- Waves
A
Secondary
- More commonly called shear waves
- Motion of individual particle is perpendicular to direction of wave motion
- Produces shearing deformation
- Cannot travel through fluids
- Vs 2-5 km/s
7
Q
Surface Waves
A
Primarily travel along the surface of the earth
- Rayleigh waves
- Love Waves
8
Q
Rayleigh Waves
A
- Surface wave
- Produced by interaction of P-waves and SV-waves with the earth surface
- Particle motion is more complex. Has components in the direction of motion and also perpendicular
9
Q
Love Waves
A
- Result from interation of SH waves with a soft layer at the ground surface
- SH waves trapped within the surficial soft layer with no vertical component of particle motion
10
Q
Which body waves travels faster
A
P-waves travel faster than S-waves
11
Q
Vp
A
P-wave velocity
12
Q
Vs
A
S-Wave velocity
13
Q
Rhypo
A
distance from source to hypocenter
14
Q
Repi
A
distance from site to epicenter
15
Q
Rrup
A
shortest distance from site to fault supture plane
16
Q
Rjb
A
is the closest distance to the surface projection of the fault
17
Q
Magnitude measures
A
size of the earthquake
18
Q
Seismic Moment magnitude
A
- a measure of work done (related to energy released) by the earthquake
19
Q
Moment magnitude
A
- A Magnitude scale based on siesmic moment
20
Q
Directionality
A
- when ground motion shakes stronger in one direction than others
- recorded directions not necessarily largest
- can average using the geometric mean
21
Q
Natural noise in ground motion
A
ocean waves, animals, wind, atmospheric pressure change
22
Q
human noise in ground motion
A
- traffic, construction, industrial process, sport events, everyday activites
23
Q
Instrumental noise in ground motion
A
digitilisation error, incorrect installation of instrument, significant instrument rocking or rotation during grouf motion, static electricity build up
24
Frequency of earthquakes
- The ground motion produced by an earthquake contains a wide range of frequencies
- Frequency content characterises what frequencies are present and with what amplitudes or energy
- Frequency content is a key parameter because dynamic response of structures may be sensitive to specific frequencies (resoant effects)
25
Fourier Spectra
Spectra of the enerfy corresponding to each frequency present in the ground motion
26
Response spectra
spectra of the responce of a simple SDOF building models over a range of vibration periods
27
Predominant period
Vibration period corresponding to the maximum value of the fourier amplitude spectrum
28
Predominant Period
Vibration period corresponding to the maximum value of the Fourier Amplitude spectrum
- Indicated what frequencies have the largest amplitudes (most energy)
29
Duration
Duration is important as longer durations mean more energy and allows for greater resonant phenomena, cumulative damage in nonlinear structures (eg stiffness degradation) and soil response (e.g. excess pore water pressure build up)
30
Bracketed duration
time interval between the first and last exceedences of a specific acceleration amplitude (usually 0.05g)
31
Uniform duration
sum of durations for which acceleration amplitudes are larger than a specific value
32
Significant Duration
Duration over which a specified percentage of the ground motion energy is released
33
Primary factors that affect ground motions
- Magnitude
- Source to Site Distance
- Site Conditions
34
Secondary factors that affect ground motions
- Faulting Style
- Source Depth
- Directivity
- Basin effects
- Topographic effects
35
Effects of magnitude on ground motions
Larger amplitude
- because there is more work done by the earthquakes rupture
Longer duration
- Because the rupture occurs across a larger fault area and therefore over a longer duration
Stronger long period content
- Because a larger rupture area can produce longer wavelengths
36
Effects if source to site distance on ground motion
Amplitude decreases with increasing distance
- geometric spreading
- Anelastic attenuation
Ground motion duration increases with increasing distance due to
- larger separation between P-waves Swaves and surface waves
- move wave scattering in the earths crust
37
Geometric Spreading
geometric spreading reduces amplitudes due to a decrease in energy density as energy spreads out over larger volumes and areas.
38
Anelastic attenuation
enelastic attenuation reduces amplitudes due to loss of energy resulting from material damping (e.g. friction) which arises during cyclic motion
- the reduction in amplitude is related to a number of cycles
- For a set distance high frequency waves will go through more cycles than low frequency waves and therefore will attenuate more
39
Effects of local site conidtions on ground motion
- Wave amplitudes re amplified when travelling from a stiff material into a soft material
- This is due to complex interactions between transmitted and reflected waves at the boundary
- However, softer soils also have high damping which reduces amplitudes as the waves travel through the soil. Damping is even larger when shaking is strong
40
3 Primary factors that influence ground motion
- Magnitude
- Source-to-site
- Site conditions
41
3 Important characyeristics of ground motion
- Amplitude
- Frequency
- Duration
42
Effects of Directivity
- Superporsition of wave amplitude occur when the direction of rupture propagation and wavefront coincide because rupture propagation velocity is similar to velocity of shear waves
