1 EPS 122: Lecture 12 – Moment tensors Moment tensors Reading: Fowler p111-140 EPS 122: Lecture 12 – Moment tensors Fault planes Rock ruptures and slides releasing stress Stress builds deforming the rock
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
EPS 122: Lecture 12 – Moment tensors
Moment tensors
Reading: Fowler p111-140
EPS 122: Lecture 12 – Moment tensors
Fault planes
Rock ruptures and slides releasing stress
Stress builds deforming the rock
2
EPS 122: Lecture 12 – Moment tensors
First motion
time
time
time
time
time
time
de
pth
What does the waveform look like?
The first motion direction observed at many stations around an earthquake can tell us the type of fault and orientation of the fault planes.
Explosive source
EPS 122: Lecture 12 – Moment tensors
San Andrea Fault
What does the waveform look like?
map view
time
time
time
time
Consider a strike-slip earthquake on the San Andreas Fault:
3
EPS 122: Lecture 12 – Moment tensors
First motion
The first motion direction observed at many stations around an earthquake can tell us the type of fault and orientation of the fault planes.
Consider a strike-slip earthquake on the San Andreas Fault:
Fault plane solutions
EPS 122: Lecture 12 – Moment tensors
Landers earthquake
InSAR image
• Radar interferogram of land surface before and after Landers
• Shows surface motion in direction of satellite viewing angle
• One fringe represents a change in distance of one wavelength (28 mm)
• 28 June, 1992
• magnitude 7.3
• strike-slip fault
• rupture 85 km long
Massonnett et al 1993
4
EPS 122: Lecture 12 – Moment tensors
Landers earthquake
InSAR image
• One fringe represents a change in distance of one wavelength (28 mm)
20 fringes
NW corner moved 56 cm
Massonnett et al 1993
EPS 122: Lecture 12 – Moment tensors
Landers earthquake
Massonnett et al 1993
5
EPS 122: Lecture 12 – Moment tensors
Landers earthquake
What would surface deformation look like?
And the slip on the fault…
mag 7.3 3-6 m slip
Massonnett et al 1993
EPS 122: Lecture 12 – Moment tensors
First motion within a sphere
In spherical Earth we plot the lower hemisphere
Fault plane solutions
Surface view
6
EPS 122: Lecture 12 – Moment tensors
Indicate fault type Fault plane solutions
…and stress regime
Transform or strike-slip
e.g. San Andreas
Normal
e.g. Mid-Ocean Ridges
Thrust or reverse
e.g. Subduction
EPS 122: Lecture 12 – Moment tensors
Mid-ocean ridges Fault plane solutions
7
EPS 122: Lecture 12 – Moment tensors
Subduction zones Fault plane solutions
ridge
EPS 122: Lecture 12 – Moment tensors
Transform Fault plane solutions
ridge subduction
8
EPS 122: Lecture 12 – Moment tensors
California Fault plane solutions
EPS 122: Lecture 12 – Moment tensors
Forces – double couple
9
EPS 122: Lecture 12 – Moment tensors
Forces
double couple compensated linear vector dipole
isotropic
EPS 122: Lecture 12 – Moment tensors
Long Valley Earthquake Moment tensor inversion
– double-couple solution
10
EPS 122: Lecture 12 – Moment tensors
Moment tensor inversion
Long Valley Earthquake – full solution
EPS 122: Lecture 12 – Moment tensors
JUNCTION explosion – Nevada test site Moment tensor inversion
11
EPS 122: Lecture 12 – Moment tensors
Bardarbunga earthquakes Volcanic earthquakes
EPS 122: Lecture 12 – Moment tensors
Bardarbunga earthquakes
Nettles and Ekström, 1998
Volcanic earthquakes
Related Documents
