The ANSS event ID is ak012dz4hkhx and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak012dz4hkhx/executive.
2012/10/30 22:02:46 61.493 -150.722 65.0 4.3 Alaska
USGS/SLU Moment Tensor Solution
ENS 2012/10/30 22:02:46:0 61.49 -150.72 65.0 4.3 Alaska
Stations used:
AK.BPAW AK.BRLK AK.CAST AK.CNP AK.EYAK AK.FIB AK.FID AK.GHO
AK.GLI AK.HIN AK.KLU AK.KNK AK.MCK AK.PPLA AK.PWL AK.RC01
AK.RND AK.SAW AK.SCM AK.SKN AK.SWD AK.TRF AT.SVW2
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 5.37e+22 dyne-cm
Mw = 4.42
Z = 66 km
Plane Strike Dip Rake
NP1 195 65 -70
NP2 334 32 -126
Principal Axes:
Axis Value Plunge Azimuth
T 5.37e+22 18 270
N 0.00e+00 18 6
P -5.37e+22 64 139
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.73e+21
Mxy 4.75e+21
Mxz 1.59e+22
Myy 4.44e+22
Myz -2.93e+22
Mzz -3.87e+22
-----------###
############-#########
###############----#########
##############--------########
###############-----------########
###############-------------########
###############----------------#######
###############------------------#######
###############-------------------######
## ##########--------------------#######
## T ##########---------------------######
## #########----------------------######
##############---------- ---------######
#############---------- P ---------#####
############----------- ---------#####
###########-----------------------####
##########----------------------####
#########----------------------###
########--------------------##
#######-------------------##
#####----------------#
#-------------
Global CMT Convention Moment Tensor:
R T P
-3.87e+22 1.59e+22 2.93e+22
1.59e+22 -5.73e+21 -4.75e+21
2.93e+22 -4.75e+21 4.44e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121030220246/index.html
|
STK = 195
DIP = 65
RAKE = -70
MW = 4.42
HS = 66.0
The NDK file is 20121030220246.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.
 |
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.
|
|
|
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:
hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 95 40 90 3.61 0.1719
WVFGRD96 1.0 55 60 -35 3.58 0.1703
WVFGRD96 2.0 90 45 85 3.76 0.2240
WVFGRD96 3.0 50 65 -40 3.75 0.2331
WVFGRD96 4.0 45 85 -30 3.75 0.2400
WVFGRD96 5.0 45 90 -30 3.78 0.2495
WVFGRD96 6.0 230 85 30 3.80 0.2562
WVFGRD96 7.0 230 85 30 3.81 0.2595
WVFGRD96 8.0 230 85 35 3.86 0.2615
WVFGRD96 9.0 230 85 30 3.86 0.2596
WVFGRD96 10.0 45 90 30 3.87 0.2613
WVFGRD96 11.0 50 75 35 3.88 0.2626
WVFGRD96 12.0 50 80 35 3.89 0.2654
WVFGRD96 13.0 50 80 35 3.90 0.2683
WVFGRD96 14.0 45 90 30 3.91 0.2707
WVFGRD96 15.0 45 90 30 3.92 0.2737
WVFGRD96 16.0 45 90 30 3.92 0.2765
WVFGRD96 17.0 45 90 30 3.93 0.2788
WVFGRD96 18.0 45 90 30 3.94 0.2815
WVFGRD96 19.0 225 85 -30 3.95 0.2849
WVFGRD96 20.0 50 85 30 3.96 0.2876
WVFGRD96 21.0 50 85 30 3.97 0.2912
WVFGRD96 22.0 50 90 30 3.98 0.2949
WVFGRD96 23.0 225 85 -30 3.99 0.2998
WVFGRD96 24.0 225 85 -30 4.00 0.3047
WVFGRD96 25.0 225 85 -30 4.01 0.3098
WVFGRD96 26.0 230 85 -30 4.03 0.3153
WVFGRD96 27.0 50 90 35 4.02 0.3205
WVFGRD96 28.0 50 90 35 4.03 0.3259
WVFGRD96 29.0 50 90 35 4.04 0.3316
WVFGRD96 30.0 230 85 -30 4.07 0.3380
WVFGRD96 31.0 230 85 -35 4.07 0.3435
WVFGRD96 32.0 225 80 -30 4.09 0.3495
WVFGRD96 33.0 225 80 -30 4.10 0.3554
WVFGRD96 34.0 230 80 -30 4.12 0.3605
WVFGRD96 35.0 225 80 -30 4.12 0.3648
WVFGRD96 36.0 230 80 -30 4.14 0.3691
WVFGRD96 37.0 225 75 -30 4.16 0.3729
WVFGRD96 38.0 225 75 -30 4.17 0.3757
WVFGRD96 39.0 225 75 -30 4.19 0.3782
WVFGRD96 40.0 220 70 -45 4.25 0.3841
WVFGRD96 41.0 220 70 -45 4.26 0.3894
WVFGRD96 42.0 220 70 -45 4.27 0.3937
WVFGRD96 43.0 220 65 -45 4.29 0.3991
WVFGRD96 44.0 220 65 -45 4.30 0.4039
WVFGRD96 45.0 220 65 -45 4.31 0.4093
WVFGRD96 46.0 220 65 -45 4.31 0.4135
WVFGRD96 47.0 215 65 -45 4.32 0.4186
WVFGRD96 48.0 215 65 -50 4.32 0.4228
WVFGRD96 49.0 215 65 -50 4.33 0.4277
WVFGRD96 50.0 215 65 -50 4.34 0.4315
WVFGRD96 51.0 205 60 -55 4.35 0.4365
WVFGRD96 52.0 205 60 -60 4.35 0.4401
WVFGRD96 53.0 205 60 -60 4.36 0.4443
WVFGRD96 54.0 200 60 -60 4.37 0.4477
WVFGRD96 55.0 200 60 -65 4.37 0.4510
WVFGRD96 56.0 200 60 -65 4.37 0.4546
WVFGRD96 57.0 200 60 -65 4.38 0.4570
WVFGRD96 58.0 200 60 -65 4.39 0.4597
WVFGRD96 59.0 195 60 -70 4.39 0.4615
WVFGRD96 60.0 195 60 -70 4.39 0.4637
WVFGRD96 61.0 195 60 -70 4.40 0.4651
WVFGRD96 62.0 195 60 -70 4.40 0.4655
WVFGRD96 63.0 195 60 -70 4.41 0.4663
WVFGRD96 64.0 200 65 -65 4.41 0.4666
WVFGRD96 65.0 200 65 -65 4.42 0.4673
WVFGRD96 66.0 195 65 -70 4.42 0.4673
WVFGRD96 67.0 195 65 -70 4.42 0.4672
WVFGRD96 68.0 195 65 -70 4.43 0.4672
WVFGRD96 69.0 195 65 -75 4.43 0.4669
WVFGRD96 70.0 195 65 -75 4.43 0.4656
WVFGRD96 71.0 195 65 -75 4.43 0.4650
WVFGRD96 72.0 195 65 -75 4.44 0.4634
WVFGRD96 73.0 195 65 -75 4.44 0.4614
WVFGRD96 74.0 190 65 -80 4.44 0.4596
WVFGRD96 75.0 190 65 -80 4.44 0.4576
WVFGRD96 76.0 190 65 -80 4.44 0.4550
WVFGRD96 77.0 190 65 -80 4.45 0.4532
WVFGRD96 78.0 190 65 -80 4.45 0.4503
WVFGRD96 79.0 190 65 -80 4.45 0.4470
WVFGRD96 80.0 190 65 -85 4.45 0.4446
WVFGRD96 81.0 190 65 -85 4.45 0.4414
WVFGRD96 82.0 190 65 -85 4.45 0.4377
WVFGRD96 83.0 190 70 -85 4.45 0.4345
WVFGRD96 84.0 190 70 -85 4.46 0.4329
WVFGRD96 85.0 190 70 -85 4.46 0.4300
WVFGRD96 86.0 5 20 -95 4.46 0.4268
WVFGRD96 87.0 0 20 -100 4.46 0.4245
WVFGRD96 88.0 5 20 -95 4.46 0.4214
WVFGRD96 89.0 0 20 -100 4.47 0.4182
WVFGRD96 90.0 5 20 -95 4.47 0.4155
WVFGRD96 91.0 190 70 -85 4.47 0.4120
WVFGRD96 92.0 190 70 -85 4.47 0.4083
WVFGRD96 93.0 0 20 -100 4.47 0.4044
WVFGRD96 94.0 0 20 -100 4.47 0.4011
WVFGRD96 95.0 190 70 -90 4.47 0.3971
WVFGRD96 96.0 -5 20 -105 4.48 0.3930
WVFGRD96 97.0 -10 20 -110 4.48 0.3892
WVFGRD96 98.0 -10 20 -110 4.48 0.3856
WVFGRD96 99.0 0 15 -100 4.48 0.3823
WVFGRD96 100.0 0 15 -100 4.48 0.3798
WVFGRD96 101.0 190 75 -85 4.48 0.3780
WVFGRD96 102.0 0 15 -100 4.48 0.3751
WVFGRD96 103.0 10 15 -90 4.48 0.3722
WVFGRD96 104.0 20 15 -80 4.48 0.3680
WVFGRD96 105.0 190 75 -85 4.49 0.3674
WVFGRD96 106.0 190 75 -85 4.49 0.3654
WVFGRD96 107.0 190 75 -85 4.49 0.3630
WVFGRD96 108.0 190 75 -85 4.49 0.3601
WVFGRD96 109.0 190 75 -85 4.49 0.3573
WVFGRD96 110.0 190 75 -85 4.49 0.3554
WVFGRD96 111.0 190 80 -80 4.49 0.3533
WVFGRD96 112.0 190 80 -80 4.50 0.3517
WVFGRD96 113.0 190 80 -80 4.50 0.3498
WVFGRD96 114.0 190 80 -80 4.50 0.3485
WVFGRD96 115.0 190 80 -80 4.50 0.3471
WVFGRD96 116.0 190 80 -80 4.50 0.3457
WVFGRD96 117.0 190 80 -80 4.50 0.3437
WVFGRD96 118.0 190 80 -80 4.50 0.3416
WVFGRD96 119.0 190 80 -80 4.51 0.3406
WVFGRD96 120.0 190 80 -80 4.51 0.3394
WVFGRD96 121.0 190 80 -80 4.51 0.3373
WVFGRD96 122.0 190 80 -80 4.51 0.3352
WVFGRD96 123.0 190 80 -80 4.51 0.3339
WVFGRD96 124.0 195 85 -80 4.52 0.3326
WVFGRD96 125.0 195 85 -80 4.52 0.3316
WVFGRD96 126.0 195 85 -80 4.52 0.3305
WVFGRD96 127.0 195 85 -80 4.53 0.3291
WVFGRD96 128.0 195 85 -80 4.53 0.3283
WVFGRD96 129.0 195 85 -80 4.53 0.3274
The best solution is
WVFGRD96 66.0 195 65 -70 4.42 0.4673
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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
hp c 0.02 n 3 lp c 0.06 n 3
|
| 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. |
|
| 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