Focal mechanisms!
Nori Nakata! Stanford University! Faulting! Faulting!
N
Strike
Dip Faulting!
N
Strike
Dip Rake Focal mechanism!
N
Strike
Dip Rake
Strike: 0-360 Dip: 0-90 Rake: 0-360 [s, d, r]=[0,90,0]!
N
Strike
Dip Rake [s, d, r]=[0,90,0]!
N
Strike
Dip Rake [s, d, r]=[0,60,0]!
N
Strike
Dip Rake [s, d, r]=[0,60,0]!
N
Strike
Dip Rake [s, d, r]=[0,90-0,0]! 90 60
30 0 [s, d, r]=[30,90,0]!
N
Strike
Dip Rake [s, d, r]=[30,90,0]!
N
Strike
Dip Rake [s, d, r]=[30,60,0]!
N
Strike
Dip Rake [s, d, r]=[30,60,0]!
N
Strike
Dip Rake [s, d, r]=[0,90,30]!
N
Strike
Dip Rake [s, d, r]=[0,90,30]!
N
Strike
Dip Rake [s, d, r]=[0,90,60]!
N
Strike
Dip Rake [s, d, r]=[0,90,60]!
N
Strike
Dip Rake [s, d, r]=[270,30,0]!
N
Strike
Dip Rake [s, d, r]=[270,30,0]!
N
Strike
Dip Rake [s, d, r]=[30,30,60]!
N
Strike
Dip Rake [s, d, r]=[30,30,60]!
N
Strike
Dip Rake [s, d, r]=[0,90,0-270]! 0 120
150 270 [s, d, r]=[30,90,0-270]! 0 120
150 270 [s, d, r]=[30,60,0-270]! 0 120
150 270 Are they enough?!
N
Strike
Dip Rake Are they enough?! Moment tensor! Moment tensor!
[s,d,r]=[0,90,0]
010 1 100 p 2 0 0001 @ A Moment tensor!
0.0566 0 0 01.7015 0 0 001.758 1 @ A Moment tensor!
0.0566 0 0 00 0 01.7015 0 01.7298 0 0 001.758 1 0 00 1.7298 1 @ A @ A
= + +
7.4e 17 0 0 0.0566 0 0 0 7.4e 17 0 0 0.0283 0 0 1 007.4e 17 0 000 .0283 1 @ A @ A Moment tensor!
= + + Moment magnitude!
1/2 1 M = M2 0 p 0 ij1 2 ij X @ A 2 M = (log M 9.1) w 3 10 0
Faulting!
N
Strike
Dip Faulting!
N
Strike
Dip Rake Faulting!
N
Strike
Dip Rake Faulting!
N
Strike
Dip Rake = 0 (left) Rake 180 (right) Rake = 270 Rake = 90 Left-lateral strike slip (rake=0)! Strike 030 6090 120 Dip
90
60
30 Right-lateral strike slip (rake=180)! Strike 030 6090 120 Dip
90
60
30 Normap-dip slip (rake=270)! Strike 030 6090 120 Dip
90
60
30 Reverse-dip slip (rake=90)! Strike 030 6090 120 Dip
90
60
30 Reverse-dip slip (rake=90)! Strike 030 6090 120 Dip
90
60
30 P and T axes! P: maximum compressive principal stress T: minimum compressive principal stress
NP2 v
v T P NP1 Radiation pattern!
Pujol (2003) Moment tensor!
= + + Characterize earthquake!
What kind of faulting?
Is the dip shallow or steep?
Is the mechanism deviatoric?
… Characterize earthquake! What kind of faulting? [s,d,r]=[30,60,180]
Is the dip shallow or steep?
Is the mechanism deviatoric?
What is the horizontal direction of faulting? Characterize earthquake!
[s,d,r]=[30,60,180] What kind of faulting? Right lateral strike slip
Is the dip shallow or steep? Steep
Is the mechanism deviatoric? Yes
What is the horizontal direction of faulting? 30 degrees from North Characterize earthquake!
[s,d,r]=[30,30,60] What kind of faulting?
Is the dip shallow or steep?
Is the mechanism deviatoric?
What is the horizontal direction of faulting?
Characterize earthquake!
[s,d,r]=[30,30,60] What kind of faulting? Mostly reverse-dip slip with some left-lateral strike slip Is the dip shallow or steep? Shallow
Is the mechanism deviatoric? Yes
What is the horizontal direction of faulting? 30 degrees from North http://earthquake.usgs.gov/ earthquakes/ What kind of faulting?
Is the dip shallow or steep (closer to 0 or 90 degrees)?
Is the mechanism deviatoric?
What is meant by “centroid”?
What kind of faulting?
What is the strike?
Is the mechanism deviatoric?
What kind of faulting?
What is the dip?
Is the mechanism deviatoric?
What kind of faulting?
Which is the fault plane?
Records! site source
path a)
0 Instrument 10 −2 10
−4 response! 10 KiK−net
Amplitude (cm/s) derivative of Hi−net
b) response−corrected Hi−net
2 10
0 10
−2 10 without correction Amplitude ratio −4 with correction 10 c) without correction with correction 360
180
0
Phase difference (deg) −1 0 1 10 10 10 Nakata (2013) Frequency (Hz)