• Author / Uploaded
• Divyanshu Lal

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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]

0

1

0 1 0 1 @ p 1 0 0 A 2 0 0 0

Moment tensor! 0

0.0566 @ 0 0

0 1.7015 0

1

0 A 0 1.758

Moment tensor! 0

0.0566 @ 0 0

0 1.7015 0

1

0

0 A 0 1.758

0 0 @ 0 1.7298 0 0

= 0 @

7.4e 0 0

1

0 A 0 1.7298

+ 17

0 7.4e 0

17

0 0 7.4e

+

17

1 A

0

0.0566 @ 0 0

1

0 0 A 0.0283 0 0 0.0283

Moment tensor!

=

+

+

Moment magnitude! 0

11/2

1 @X 2 A Mij M0 = p 2 ij 2 Mw = (log10 M0 3

9.1)

Faulting! N

Strike

Dip

Faulting! N

Strike

Dip

Rake

Faulting! N

Strike

Dip

Rake

Faulting! N

Strike

Rake = 0 (left) 180 (right)

Dip

Rake

Rake = 270

Rake = 90

Left-lateral strike slip (rake=0)! Dip 90

60

30

0

30

Strike 60

90

120

Right-lateral strike slip (rake=180)! Dip 90

60

30

0

30

Strike 60

90

120

Normap-dip slip (rake=270)! Dip 90

60

30

0

30

Strike 60

90

120

Reverse-dip slip (rake=90)! Dip 90

60

30

0

30

Strike 60

90

120

Reverse-dip slip (rake=90)! Dip 90

60

30

0

30

Strike 60

90

120

P and T axes! P: maximum compressive principal stress T: minimum compressive principal stress

NP2

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! [s,d,r]=[30,60,180]

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]=[30,60,180]

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) Amplitude (cm/s) Amplitude ratio

Instrument response!

0

10

10

−2

10

−4

KiK−net derivative of Hi−net response−corrected Hi−net

10

b) 2

0

10

−2

10

without correction with correction

−4

Nakata (2013)

Phase difference (deg)

c)

10

without correction with correction

360 180 0 −1

10

0

1

10 10 Frequency (Hz)