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Focal Mechanisms! 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).
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