The ANSS event ID is ak0166j12cvm and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0166j12cvm/executive.
2016/05/21 11:34:09 62.360 -152.463 143.5 4.5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2016/05/21 11:34:09:0 62.36 -152.46 143.5 4.5 Alaska
Stations used:
AK.CUT AK.EYAK AK.HDA AK.KNK AK.NEA2 AK.PAX AK.PPLA AK.RC01
AK.RIDG AK.SAW AK.SWD AT.PMR AT.SVW2 AT.TTA IM.IL31 IU.COLA
TA.H21K TA.H23K TA.H24K TA.I21K TA.I23K TA.J20K TA.K20K
TA.L19K TA.M22K TA.M24K TA.N18K TA.N19K TA.N25K TA.O19K
TA.O22K TA.P18K TA.POKR
Filtering commands used:
cut a -20 a 80
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 5.75e+22 dyne-cm
Mw = 4.44
Z = 146 km
Plane Strike Dip Rake
NP1 355 86 87
NP2 215 5 130
Principal Axes:
Axis Value Plunge Azimuth
T 5.75e+22 49 261
N 0.00e+00 3 355
P -5.75e+22 41 88
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.11e+20
Mxy 2.49e+21
Mxz -5.28e+21
Myy -8.17e+21
Myz -5.67e+22
Mzz 7.65e+21
--###---------
--########------------
--###########---------------
-#############----------------
-################-----------------
-#################------------------
-##################-------------------
-###################--------------------
-####################-------------------
-#####################---------- -------
-######## ##########---------- P -------
-######## T ##########---------- -------
-######## ##########--------------------
#####################-------------------
-####################-------------------
#####################-----------------
####################----------------
###################---------------
#################-------------
-###############------------
#############---------
#########-----
Global CMT Convention Moment Tensor:
R T P
7.65e+21 -5.28e+21 5.67e+22
-5.28e+21 5.11e+20 -2.49e+21
5.67e+22 -2.49e+21 -8.17e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160521113409/index.html
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STK = 35
DIP = -5
RAKE = -50
MW = 4.44
HS = 146.0
The NDK file is 20160521113409.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) the waveform inversion are shown in the next figure.
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The program wvfgrd96 was used with good traces observed at short distance to determine the focal mechanism, depth and seismic moment. This technique requires a high quality signal and well determined velocity model for the Green's functions. To the extent that these are the quality data, this type of mechanism should be preferred over the radiation pattern technique which requires the separate step of defining the pressure and tension quadrants and the correct strike.
The observed and predicted traces are filtered using the following gsac commands:
cut a -20 a 80 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 60 90 10 3.40 0.1842
WVFGRD96 4.0 240 80 -10 3.51 0.2084
WVFGRD96 6.0 240 90 -15 3.57 0.2131
WVFGRD96 8.0 240 90 -15 3.64 0.2256
WVFGRD96 10.0 60 85 15 3.67 0.2327
WVFGRD96 12.0 60 85 15 3.71 0.2372
WVFGRD96 14.0 60 85 10 3.74 0.2405
WVFGRD96 16.0 60 75 -5 3.77 0.2417
WVFGRD96 18.0 60 75 5 3.78 0.2389
WVFGRD96 20.0 60 75 5 3.80 0.2302
WVFGRD96 22.0 60 75 10 3.81 0.2174
WVFGRD96 24.0 150 75 5 3.82 0.2106
WVFGRD96 26.0 150 70 5 3.84 0.2163
WVFGRD96 28.0 150 70 5 3.86 0.2193
WVFGRD96 30.0 150 75 10 3.88 0.2255
WVFGRD96 32.0 150 75 10 3.90 0.2335
WVFGRD96 34.0 150 85 15 3.93 0.2406
WVFGRD96 36.0 330 90 -15 3.97 0.2504
WVFGRD96 38.0 330 90 -10 4.01 0.2649
WVFGRD96 40.0 155 85 15 4.08 0.2872
WVFGRD96 42.0 155 85 15 4.11 0.2993
WVFGRD96 44.0 330 90 -15 4.13 0.3071
WVFGRD96 46.0 330 90 -10 4.15 0.3137
WVFGRD96 48.0 330 90 -10 4.17 0.3188
WVFGRD96 50.0 155 85 15 4.19 0.3267
WVFGRD96 52.0 335 90 -15 4.21 0.3282
WVFGRD96 54.0 155 85 15 4.22 0.3358
WVFGRD96 56.0 155 80 15 4.23 0.3393
WVFGRD96 58.0 155 80 10 4.24 0.3431
WVFGRD96 60.0 155 80 10 4.24 0.3470
WVFGRD96 62.0 155 80 5 4.25 0.3514
WVFGRD96 64.0 155 80 5 4.25 0.3554
WVFGRD96 66.0 155 80 5 4.26 0.3576
WVFGRD96 68.0 150 85 -10 4.24 0.3619
WVFGRD96 70.0 150 85 -15 4.24 0.3670
WVFGRD96 72.0 150 85 -20 4.25 0.3733
WVFGRD96 74.0 150 85 -20 4.25 0.3804
WVFGRD96 76.0 150 85 -25 4.25 0.3866
WVFGRD96 78.0 150 85 -25 4.26 0.3931
WVFGRD96 80.0 150 85 -25 4.26 0.3993
WVFGRD96 82.0 150 85 -30 4.26 0.4039
WVFGRD96 84.0 150 85 -30 4.27 0.4100
WVFGRD96 86.0 150 85 -30 4.27 0.4157
WVFGRD96 88.0 165 90 -40 4.28 0.4205
WVFGRD96 90.0 165 90 -45 4.29 0.4294
WVFGRD96 92.0 160 90 -50 4.29 0.4402
WVFGRD96 94.0 160 90 -55 4.30 0.4517
WVFGRD96 96.0 160 90 -55 4.31 0.4631
WVFGRD96 98.0 160 90 -60 4.31 0.4736
WVFGRD96 100.0 160 90 -60 4.32 0.4845
WVFGRD96 102.0 340 90 65 4.33 0.4966
WVFGRD96 104.0 160 90 -70 4.34 0.5090
WVFGRD96 106.0 160 90 -70 4.35 0.5207
WVFGRD96 108.0 160 90 -70 4.35 0.5313
WVFGRD96 110.0 160 90 -70 4.36 0.5411
WVFGRD96 112.0 165 90 -75 4.37 0.5505
WVFGRD96 114.0 345 85 80 4.38 0.5671
WVFGRD96 116.0 345 85 80 4.38 0.5766
WVFGRD96 118.0 350 85 80 4.38 0.5853
WVFGRD96 120.0 350 85 85 4.40 0.5940
WVFGRD96 122.0 350 85 85 4.40 0.6022
WVFGRD96 124.0 350 85 85 4.40 0.6097
WVFGRD96 126.0 350 85 85 4.41 0.6158
WVFGRD96 128.0 170 90 -80 4.41 0.5997
WVFGRD96 130.0 170 90 -80 4.41 0.6038
WVFGRD96 132.0 350 85 85 4.41 0.6308
WVFGRD96 134.0 355 85 85 4.42 0.6345
WVFGRD96 136.0 140 5 55 4.44 0.6332
WVFGRD96 138.0 130 5 45 4.44 0.6338
WVFGRD96 140.0 130 5 45 4.44 0.6355
WVFGRD96 142.0 165 5 80 4.43 0.6390
WVFGRD96 144.0 15 -5 -70 4.43 0.6422
WVFGRD96 146.0 35 -5 -50 4.44 0.6434
WVFGRD96 148.0 180 90 -90 4.46 0.6203
WVFGRD96 150.0 165 5 80 4.44 0.6352
WVFGRD96 152.0 40 -5 -45 4.44 0.6367
WVFGRD96 154.0 -5 85 85 4.43 0.6311
WVFGRD96 156.0 25 -5 -60 4.44 0.6297
WVFGRD96 158.0 -5 85 85 4.43 0.6231
WVFGRD96 160.0 180 90 -90 4.46 0.6048
WVFGRD96 162.0 155 5 70 4.44 0.6102
WVFGRD96 164.0 165 5 80 4.43 0.6048
WVFGRD96 166.0 165 5 80 4.43 0.5974
WVFGRD96 168.0 185 5 100 4.43 0.5938
The best solution is
WVFGRD96 146.0 35 -5 -50 4.44 0.6434
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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The comparison of the observed and predicted waveforms is given in the next figure. The red traces are the observed and the blue are the predicted. Each observed-predicted component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number it the time shift required for maximum correlation between the observed and predicted traces. This time shift is required because the synthetics are not computed at exactly the same distance as the observed, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. A positive time shift indicates that the prediction is too fast and should be delayed to match the observed trace (shift to the right in this figure). A negative value indicates that the prediction is too slow. The lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
cut a -20 a 80 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3
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| Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. Each solution is plotted as a vector at a given value of strike and dip with the angle of the vector representing the rake angle, measured, with respect to the upward vertical (N) in the figure. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
MODEL.01
Model after 8 iterations
ISOTROPIC
KGS
FLAT EARTH
1-D
CONSTANT VELOCITY
LINE08
LINE09
LINE10
LINE11
H(KM) VP(KM/S) VS(KM/S) RHO(GM/CC) QP QS ETAP ETAS FREFP FREFS
1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00
6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00
13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00
19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 0.00 0.00 1.00 1.00