The ANSS event ID is ak0139xclbxw and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0139xclbxw/executive.
2013/08/04 07:57:54 61.440 -149.861 36.7 3.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/08/04 07:57:54:0 61.44 -149.86 36.7 3.8 Alaska
Stations used:
AK.FID AK.GHO AK.GLI AK.RC01 AK.SAW AK.SCM AK.SKN AK.SSN
AK.SWD AT.PMR
Filtering commands used:
cut a -30 a 120
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.02e+22 dyne-cm
Mw = 3.94
Z = 48 km
Plane Strike Dip Rake
NP1 220 70 -60
NP2 341 36 -144
Principal Axes:
Axis Value Plunge Azimuth
T 1.02e+22 19 288
N 0.00e+00 28 29
P -1.02e+22 55 168
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.38e+21
Mxy -1.97e+21
Mxz 5.70e+21
Myy 8.08e+21
Myz -4.08e+21
Mzz -5.70e+21
##------------
############----------
##################---------#
######################-#######
######################---#########
#####################-------########
####################----------########
## ##############-------------########
## T ############----------------#######
### ###########-----------------########
###############--------------------#######
##############---------------------#######
#############----------------------#######
###########-----------------------######
##########---------- -----------######
########----------- P -----------#####
######------------ ----------#####
####-------------------------#####
##-------------------------###
#-----------------------####
--------------------##
--------------
Global CMT Convention Moment Tensor:
R T P
-5.70e+21 5.70e+21 4.08e+21
5.70e+21 -2.38e+21 1.97e+21
4.08e+21 1.97e+21 8.08e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130804075754/index.html
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STK = 220
DIP = 70
RAKE = -60
MW = 3.94
HS = 48.0
The NDK file is 20130804075754.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 -30 a 120 rtr taper w 0.1 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 25 45 95 3.22 0.2646
WVFGRD96 1.0 195 45 90 3.24 0.2639
WVFGRD96 2.0 195 45 85 3.37 0.3455
WVFGRD96 3.0 190 50 80 3.42 0.3495
WVFGRD96 4.0 15 45 -90 3.46 0.3490
WVFGRD96 5.0 225 80 -10 3.42 0.3568
WVFGRD96 6.0 230 80 -5 3.43 0.3698
WVFGRD96 7.0 240 70 -5 3.45 0.3841
WVFGRD96 8.0 240 70 -5 3.48 0.3995
WVFGRD96 9.0 70 60 30 3.52 0.4079
WVFGRD96 10.0 70 65 30 3.54 0.4211
WVFGRD96 11.0 70 65 30 3.55 0.4354
WVFGRD96 12.0 70 65 30 3.56 0.4482
WVFGRD96 13.0 70 65 30 3.57 0.4591
WVFGRD96 14.0 70 65 30 3.59 0.4689
WVFGRD96 15.0 75 65 25 3.60 0.4779
WVFGRD96 16.0 70 70 30 3.61 0.4864
WVFGRD96 17.0 70 70 25 3.62 0.4941
WVFGRD96 18.0 70 70 25 3.63 0.5017
WVFGRD96 19.0 70 70 25 3.64 0.5087
WVFGRD96 20.0 70 70 25 3.65 0.5149
WVFGRD96 21.0 230 70 -35 3.67 0.5248
WVFGRD96 22.0 230 70 -40 3.68 0.5381
WVFGRD96 23.0 230 70 -40 3.69 0.5510
WVFGRD96 24.0 230 70 -40 3.69 0.5626
WVFGRD96 25.0 230 70 -40 3.70 0.5735
WVFGRD96 26.0 230 70 -40 3.71 0.5841
WVFGRD96 27.0 230 70 -40 3.72 0.5927
WVFGRD96 28.0 230 70 -40 3.72 0.6011
WVFGRD96 29.0 230 70 -40 3.73 0.6077
WVFGRD96 30.0 230 75 -45 3.74 0.6139
WVFGRD96 31.0 230 75 -45 3.75 0.6221
WVFGRD96 32.0 230 75 -45 3.75 0.6282
WVFGRD96 33.0 225 70 -45 3.76 0.6350
WVFGRD96 34.0 225 70 -45 3.76 0.6400
WVFGRD96 35.0 225 70 -45 3.77 0.6465
WVFGRD96 36.0 225 70 -45 3.78 0.6519
WVFGRD96 37.0 225 70 -45 3.79 0.6571
WVFGRD96 38.0 225 70 -45 3.79 0.6608
WVFGRD96 39.0 220 70 -45 3.81 0.6654
WVFGRD96 40.0 225 70 -60 3.90 0.6622
WVFGRD96 41.0 225 70 -55 3.90 0.6680
WVFGRD96 42.0 225 70 -55 3.91 0.6723
WVFGRD96 43.0 220 70 -55 3.91 0.6768
WVFGRD96 44.0 220 70 -55 3.92 0.6795
WVFGRD96 45.0 220 70 -55 3.93 0.6821
WVFGRD96 46.0 220 70 -55 3.93 0.6832
WVFGRD96 47.0 220 70 -60 3.94 0.6838
WVFGRD96 48.0 220 70 -60 3.94 0.6840
WVFGRD96 49.0 220 70 -60 3.95 0.6833
WVFGRD96 50.0 220 70 -60 3.95 0.6823
WVFGRD96 51.0 220 70 -60 3.95 0.6802
WVFGRD96 52.0 220 70 -60 3.96 0.6782
WVFGRD96 53.0 220 70 -60 3.96 0.6753
WVFGRD96 54.0 220 70 -60 3.96 0.6726
WVFGRD96 55.0 220 70 -60 3.96 0.6693
WVFGRD96 56.0 220 70 -60 3.97 0.6651
WVFGRD96 57.0 220 70 -60 3.97 0.6616
WVFGRD96 58.0 220 70 -60 3.97 0.6563
WVFGRD96 59.0 215 70 -60 3.97 0.6534
WVFGRD96 60.0 215 70 -60 3.98 0.6491
WVFGRD96 61.0 215 70 -60 3.98 0.6452
WVFGRD96 62.0 215 70 -60 3.98 0.6407
WVFGRD96 63.0 215 70 -60 3.98 0.6363
WVFGRD96 64.0 215 70 -60 3.98 0.6329
WVFGRD96 65.0 215 70 -60 3.98 0.6282
WVFGRD96 66.0 215 70 -60 3.98 0.6239
WVFGRD96 67.0 215 70 -60 3.99 0.6205
WVFGRD96 68.0 215 70 -60 3.99 0.6153
WVFGRD96 69.0 215 70 -60 3.99 0.6115
WVFGRD96 70.0 215 70 -60 3.99 0.6073
WVFGRD96 71.0 215 70 -60 3.99 0.6022
WVFGRD96 72.0 215 70 -60 3.99 0.5988
WVFGRD96 73.0 215 70 -60 3.99 0.5944
WVFGRD96 74.0 215 70 -60 3.99 0.5894
WVFGRD96 75.0 215 70 -60 3.99 0.5861
WVFGRD96 76.0 215 75 -60 4.00 0.5818
WVFGRD96 77.0 215 75 -60 4.00 0.5786
WVFGRD96 78.0 215 75 -60 4.00 0.5755
WVFGRD96 79.0 215 75 -60 4.00 0.5730
WVFGRD96 80.0 215 75 -65 4.00 0.5697
WVFGRD96 81.0 215 75 -65 4.01 0.5665
WVFGRD96 82.0 215 75 -65 4.01 0.5644
WVFGRD96 83.0 215 75 -65 4.01 0.5612
WVFGRD96 84.0 215 75 -65 4.01 0.5580
WVFGRD96 85.0 215 75 -65 4.01 0.5555
WVFGRD96 86.0 215 75 -65 4.01 0.5532
WVFGRD96 87.0 215 75 -70 4.01 0.5495
WVFGRD96 88.0 215 80 -70 4.02 0.5476
WVFGRD96 89.0 215 80 -70 4.02 0.5458
WVFGRD96 90.0 215 80 -70 4.03 0.5443
WVFGRD96 91.0 215 80 -75 4.03 0.5415
WVFGRD96 92.0 215 80 -75 4.03 0.5409
WVFGRD96 93.0 215 80 -80 4.04 0.5389
WVFGRD96 94.0 215 80 -85 4.05 0.5373
WVFGRD96 95.0 215 80 -85 4.05 0.5357
WVFGRD96 96.0 215 80 -85 4.05 0.5346
WVFGRD96 97.0 215 80 -85 4.05 0.5329
WVFGRD96 98.0 215 80 -85 4.05 0.5308
WVFGRD96 99.0 215 80 -85 4.05 0.5292
WVFGRD96 100.0 215 80 -85 4.05 0.5273
WVFGRD96 101.0 215 80 -85 4.06 0.5256
WVFGRD96 102.0 15 10 -110 4.06 0.5229
WVFGRD96 103.0 15 10 -110 4.06 0.5215
WVFGRD96 104.0 215 80 -90 4.07 0.5190
WVFGRD96 105.0 15 10 -110 4.06 0.5173
WVFGRD96 106.0 15 10 -110 4.06 0.5147
WVFGRD96 107.0 215 80 -90 4.07 0.5118
WVFGRD96 108.0 215 80 -90 4.07 0.5102
WVFGRD96 109.0 215 80 -90 4.07 0.5073
WVFGRD96 110.0 50 10 -75 4.08 0.5050
WVFGRD96 111.0 50 10 -70 4.08 0.5025
WVFGRD96 112.0 60 10 -60 4.09 0.5002
WVFGRD96 113.0 60 10 -60 4.09 0.4983
WVFGRD96 114.0 60 10 -60 4.09 0.4955
WVFGRD96 115.0 65 10 -55 4.10 0.4927
WVFGRD96 116.0 65 10 -55 4.10 0.4908
WVFGRD96 117.0 65 10 -55 4.10 0.4879
WVFGRD96 118.0 65 10 -55 4.10 0.4858
WVFGRD96 119.0 70 10 -50 4.10 0.4829
WVFGRD96 120.0 70 10 -50 4.10 0.4800
WVFGRD96 121.0 70 10 -50 4.10 0.4781
WVFGRD96 122.0 50 5 -70 4.10 0.4753
WVFGRD96 123.0 50 5 -70 4.10 0.4726
WVFGRD96 124.0 50 5 -70 4.10 0.4698
WVFGRD96 125.0 60 5 -60 4.10 0.4669
WVFGRD96 126.0 60 5 -60 4.10 0.4647
WVFGRD96 127.0 60 5 -60 4.10 0.4622
WVFGRD96 128.0 60 5 -60 4.11 0.4590
WVFGRD96 129.0 60 5 -60 4.11 0.4565
The best solution is
WVFGRD96 48.0 220 70 -60 3.94 0.6840
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 -30 a 120 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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