The ANSS event ID is ak013bo3451v and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak013bo3451v/executive.
2013/09/11 01:02:59 61.348 -149.512 41.3 4 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/09/11 01:02:59:0 61.35 -149.51 41.3 4.0 Alaska
Stations used:
AK.CAPN AK.CAST AK.EYAK AK.GLI AK.HDA AK.KNK AK.PAX AK.PPLA
AK.PTPK AK.RC01 AK.SAW AK.SCM AK.SKN AK.SLK AK.SWD AK.TGL
AK.WAT1 AK.WAT2 AK.WAT3 AK.WAT4 AK.WAT6 AK.WAT7 AK.WAX
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.22e+22 dyne-cm
Mw = 3.99
Z = 45 km
Plane Strike Dip Rake
NP1 143 57 -130
NP2 20 50 -45
Principal Axes:
Axis Value Plunge Azimuth
T 1.22e+22 4 260
N 0.00e+00 33 167
P -1.22e+22 57 356
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.24e+21
Mxy 2.32e+21
Mxz -5.71e+21
Myy 1.17e+22
Myz -4.87e+20
Mzz -8.47e+21
--------------
-------------------###
#----------------------#####
##-----------------------#####
####------------------------######
#####----------- ----------#######
######----------- P ----------########
########---------- ----------#########
########-----------------------#########
##########----------------------##########
###########---------------------##########
############-------------------###########
##########------------------###########
T ###########----------------###########
#############-------------############
###############-----------############
################--------############
#################-----############
##############################
###############-------######
#########-------------
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Global CMT Convention Moment Tensor:
R T P
-8.47e+21 -5.71e+21 4.87e+20
-5.71e+21 -3.24e+21 -2.32e+21
4.87e+20 -2.32e+21 1.17e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130911010259/index.html
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STK = 20
DIP = 50
RAKE = -45
MW = 3.99
HS = 45.0
The NDK file is 20130911010259.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 180 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 0.5 170 45 95 3.25 0.1964
WVFGRD96 1.0 345 45 90 3.29 0.1977
WVFGRD96 2.0 170 45 95 3.40 0.2549
WVFGRD96 3.0 345 45 90 3.47 0.2651
WVFGRD96 4.0 135 80 -20 3.47 0.2450
WVFGRD96 5.0 130 70 -30 3.51 0.2545
WVFGRD96 6.0 130 70 -30 3.52 0.2616
WVFGRD96 7.0 130 70 -25 3.54 0.2693
WVFGRD96 8.0 130 70 -30 3.58 0.2738
WVFGRD96 9.0 130 70 -30 3.59 0.2747
WVFGRD96 10.0 130 85 -40 3.56 0.2793
WVFGRD96 11.0 130 85 -40 3.57 0.2898
WVFGRD96 12.0 45 45 25 3.57 0.3051
WVFGRD96 13.0 45 50 25 3.60 0.3256
WVFGRD96 14.0 45 50 25 3.61 0.3444
WVFGRD96 15.0 45 50 25 3.62 0.3614
WVFGRD96 16.0 45 55 20 3.64 0.3775
WVFGRD96 17.0 45 55 20 3.66 0.3927
WVFGRD96 18.0 45 55 20 3.67 0.4065
WVFGRD96 19.0 40 55 15 3.67 0.4191
WVFGRD96 20.0 40 55 15 3.68 0.4308
WVFGRD96 21.0 40 55 15 3.70 0.4417
WVFGRD96 22.0 30 55 -20 3.71 0.4551
WVFGRD96 23.0 30 55 -20 3.72 0.4677
WVFGRD96 24.0 30 60 -25 3.74 0.4804
WVFGRD96 25.0 30 60 -25 3.75 0.4923
WVFGRD96 26.0 30 60 -25 3.76 0.5038
WVFGRD96 27.0 30 60 -25 3.77 0.5147
WVFGRD96 28.0 25 60 -30 3.78 0.5256
WVFGRD96 29.0 25 60 -30 3.78 0.5366
WVFGRD96 30.0 25 60 -30 3.79 0.5470
WVFGRD96 31.0 25 60 -30 3.80 0.5567
WVFGRD96 32.0 25 60 -30 3.81 0.5657
WVFGRD96 33.0 25 60 -30 3.82 0.5740
WVFGRD96 34.0 25 60 -30 3.83 0.5810
WVFGRD96 35.0 25 60 -30 3.84 0.5865
WVFGRD96 36.0 25 60 -30 3.85 0.5909
WVFGRD96 37.0 25 60 -30 3.86 0.5934
WVFGRD96 38.0 25 60 -30 3.87 0.5941
WVFGRD96 39.0 25 60 -30 3.88 0.5924
WVFGRD96 40.0 20 50 -40 3.95 0.6031
WVFGRD96 41.0 20 50 -40 3.96 0.6085
WVFGRD96 42.0 20 50 -45 3.98 0.6119
WVFGRD96 43.0 20 50 -45 3.98 0.6143
WVFGRD96 44.0 20 50 -45 3.99 0.6155
WVFGRD96 45.0 20 50 -45 3.99 0.6162
WVFGRD96 46.0 20 50 -45 4.00 0.6157
WVFGRD96 47.0 20 50 -45 4.01 0.6148
WVFGRD96 48.0 20 50 -40 4.01 0.6134
WVFGRD96 49.0 20 50 -40 4.01 0.6120
WVFGRD96 50.0 20 50 -40 4.02 0.6100
WVFGRD96 51.0 20 50 -40 4.02 0.6079
WVFGRD96 52.0 20 50 -40 4.03 0.6059
WVFGRD96 53.0 20 50 -40 4.03 0.6031
WVFGRD96 54.0 20 50 -40 4.03 0.6007
WVFGRD96 55.0 20 50 -40 4.04 0.5978
WVFGRD96 56.0 25 50 -35 4.04 0.5954
WVFGRD96 57.0 25 50 -35 4.05 0.5934
WVFGRD96 58.0 25 50 -35 4.05 0.5915
WVFGRD96 59.0 25 50 -35 4.06 0.5892
WVFGRD96 60.0 25 50 -35 4.06 0.5871
WVFGRD96 61.0 25 50 -35 4.06 0.5848
WVFGRD96 62.0 25 50 -35 4.07 0.5820
WVFGRD96 63.0 25 50 -35 4.07 0.5791
WVFGRD96 64.0 25 50 -35 4.08 0.5762
WVFGRD96 65.0 30 50 -30 4.08 0.5737
WVFGRD96 66.0 30 50 -30 4.09 0.5714
WVFGRD96 67.0 30 50 -30 4.09 0.5692
WVFGRD96 68.0 30 50 -30 4.09 0.5671
WVFGRD96 69.0 30 50 -30 4.10 0.5641
WVFGRD96 70.0 30 50 -30 4.10 0.5613
WVFGRD96 71.0 30 50 -25 4.10 0.5585
WVFGRD96 72.0 30 50 -25 4.10 0.5555
WVFGRD96 73.0 30 50 -25 4.11 0.5529
WVFGRD96 74.0 30 50 -25 4.11 0.5496
WVFGRD96 75.0 30 50 -25 4.11 0.5460
WVFGRD96 76.0 30 45 -25 4.11 0.5435
WVFGRD96 77.0 30 45 -25 4.11 0.5407
WVFGRD96 78.0 30 45 -25 4.12 0.5382
WVFGRD96 79.0 30 45 -25 4.12 0.5354
WVFGRD96 80.0 30 45 -25 4.12 0.5324
WVFGRD96 81.0 30 45 -25 4.13 0.5294
WVFGRD96 82.0 30 45 -25 4.13 0.5258
WVFGRD96 83.0 30 45 -25 4.13 0.5230
WVFGRD96 84.0 30 45 -25 4.14 0.5193
WVFGRD96 85.0 30 45 -25 4.14 0.5159
WVFGRD96 86.0 30 45 -25 4.14 0.5123
WVFGRD96 87.0 30 45 -25 4.14 0.5086
WVFGRD96 88.0 30 45 -25 4.14 0.5046
WVFGRD96 89.0 30 45 -25 4.15 0.5012
WVFGRD96 90.0 35 45 -20 4.16 0.4975
WVFGRD96 91.0 35 45 -20 4.16 0.4937
WVFGRD96 92.0 35 45 -20 4.16 0.4901
WVFGRD96 93.0 35 45 -20 4.17 0.4864
WVFGRD96 94.0 35 45 -20 4.17 0.4824
WVFGRD96 95.0 35 45 -20 4.17 0.4788
WVFGRD96 96.0 35 45 -20 4.17 0.4744
WVFGRD96 97.0 35 45 -20 4.17 0.4707
WVFGRD96 98.0 35 45 -20 4.17 0.4664
WVFGRD96 99.0 35 45 -20 4.18 0.4625
The best solution is
WVFGRD96 45.0 20 50 -45 3.99 0.6162
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 180 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