The ANSS event ID is ak01289s26wj and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak01289s26wj/executive.
2012/06/28 05:58:57 62.465 -148.315 56.4 3.5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2012/06/28 05:58:57:0 62.47 -148.32 56.4 3.5 Alaska
Stations used:
AK.BWN AK.DHY AK.KTH AK.PPLA AK.SAW AK.TRF AT.PMR
Filtering commands used:
hp c 0.025 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 4.47e+21 dyne-cm
Mw = 3.70
Z = 79 km
Plane Strike Dip Rake
NP1 214 55 -93
NP2 40 35 -85
Principal Axes:
Axis Value Plunge Azimuth
T 4.47e+21 10 306
N 0.00e+00 3 216
P -4.47e+21 79 110
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.51e+21
Mxy -2.02e+21
Mxz 7.34e+20
Myy 2.67e+21
Myz -1.37e+21
Mzz -4.18e+21
##############
######################
###################--------#
###############------------#
# T ############----------------##
## ##########-------------------##
##############---------------------###
##############----------------------####
#############-----------------------####
############-------------------------#####
###########----------- -----------######
###########----------- P -----------######
##########------------ ----------#######
########-------------------------#######
########------------------------########
#######-----------------------########
#####----------------------#########
####--------------------##########
###----------------###########
##-------------#############
######################
##############
Global CMT Convention Moment Tensor:
R T P
-4.18e+21 7.34e+20 1.37e+21
7.34e+20 1.51e+21 2.02e+21
1.37e+21 2.02e+21 2.67e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120628055857/index.html
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STK = 40
DIP = 35
RAKE = -85
MW = 3.70
HS = 79.0
The NDK file is 20120628055857.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:
hp c 0.025 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 90 45 85 2.63 0.1827
WVFGRD96 1.0 65 90 0 2.77 0.1968
WVFGRD96 2.0 245 90 0 2.90 0.2308
WVFGRD96 3.0 245 90 0 3.02 0.2407
WVFGRD96 4.0 60 70 -15 3.01 0.2082
WVFGRD96 5.0 60 70 -20 3.03 0.2236
WVFGRD96 6.0 60 70 -15 3.07 0.2467
WVFGRD96 7.0 60 70 -15 3.09 0.2648
WVFGRD96 8.0 60 65 -15 3.16 0.2818
WVFGRD96 9.0 200 35 20 2.97 0.2888
WVFGRD96 10.0 195 40 15 3.00 0.2998
WVFGRD96 11.0 190 45 5 3.02 0.3048
WVFGRD96 12.0 180 50 -5 3.05 0.3129
WVFGRD96 13.0 180 50 -5 3.06 0.3104
WVFGRD96 14.0 180 50 -5 3.08 0.3129
WVFGRD96 15.0 180 50 -5 3.09 0.3125
WVFGRD96 16.0 145 60 40 3.15 0.3016
WVFGRD96 17.0 145 60 40 3.17 0.3022
WVFGRD96 18.0 145 55 45 3.17 0.3020
WVFGRD96 19.0 140 55 45 3.18 0.3041
WVFGRD96 20.0 135 55 45 3.18 0.3051
WVFGRD96 21.0 135 55 45 3.20 0.3065
WVFGRD96 22.0 135 55 45 3.22 0.3059
WVFGRD96 23.0 120 60 40 3.22 0.3074
WVFGRD96 24.0 285 60 -50 3.20 0.3085
WVFGRD96 25.0 280 60 -50 3.21 0.3083
WVFGRD96 26.0 280 65 -50 3.22 0.3057
WVFGRD96 27.0 120 65 35 3.25 0.3106
WVFGRD96 28.0 120 65 35 3.26 0.3156
WVFGRD96 29.0 110 70 35 3.27 0.3186
WVFGRD96 30.0 140 60 45 3.30 0.3199
WVFGRD96 31.0 140 60 45 3.31 0.3245
WVFGRD96 32.0 145 65 35 3.34 0.3285
WVFGRD96 33.0 270 70 -40 3.30 0.3326
WVFGRD96 34.0 275 70 -45 3.30 0.3432
WVFGRD96 35.0 265 65 -45 3.33 0.3548
WVFGRD96 36.0 265 65 -45 3.35 0.3647
WVFGRD96 37.0 265 65 -45 3.36 0.3741
WVFGRD96 38.0 265 65 -45 3.37 0.3809
WVFGRD96 39.0 265 60 -45 3.39 0.3890
WVFGRD96 40.0 255 60 -55 3.51 0.4159
WVFGRD96 41.0 255 60 -55 3.52 0.4153
WVFGRD96 42.0 260 65 -45 3.52 0.4110
WVFGRD96 43.0 260 65 -45 3.53 0.4104
WVFGRD96 44.0 260 65 -45 3.54 0.4085
WVFGRD96 45.0 260 65 -45 3.55 0.4070
WVFGRD96 46.0 135 35 -10 3.57 0.4137
WVFGRD96 47.0 120 25 -30 3.57 0.4278
WVFGRD96 48.0 100 20 -50 3.57 0.4413
WVFGRD96 49.0 100 20 -50 3.57 0.4534
WVFGRD96 50.0 245 70 -85 3.57 0.4644
WVFGRD96 51.0 260 75 -55 3.57 0.4750
WVFGRD96 52.0 260 75 -55 3.58 0.4857
WVFGRD96 53.0 260 75 -55 3.58 0.4954
WVFGRD96 54.0 260 75 -50 3.60 0.5025
WVFGRD96 55.0 260 75 -50 3.60 0.5089
WVFGRD96 56.0 225 55 -90 3.66 0.5233
WVFGRD96 57.0 225 55 -90 3.66 0.5321
WVFGRD96 58.0 225 55 -90 3.66 0.5399
WVFGRD96 59.0 225 55 -90 3.66 0.5465
WVFGRD96 60.0 225 55 -90 3.66 0.5508
WVFGRD96 61.0 225 55 -90 3.66 0.5562
WVFGRD96 62.0 225 55 -90 3.66 0.5601
WVFGRD96 63.0 225 55 -90 3.66 0.5646
WVFGRD96 64.0 225 55 -90 3.65 0.5671
WVFGRD96 65.0 225 55 -90 3.65 0.5699
WVFGRD96 66.0 220 55 -90 3.67 0.5721
WVFGRD96 67.0 220 55 -90 3.67 0.5748
WVFGRD96 68.0 220 55 -90 3.67 0.5785
WVFGRD96 69.0 220 55 -90 3.67 0.5807
WVFGRD96 70.0 220 55 -90 3.67 0.5824
WVFGRD96 71.0 220 55 -90 3.67 0.5843
WVFGRD96 72.0 220 55 -90 3.67 0.5848
WVFGRD96 73.0 220 55 -90 3.68 0.5875
WVFGRD96 74.0 220 55 -90 3.68 0.5888
WVFGRD96 75.0 220 55 -90 3.68 0.5891
WVFGRD96 76.0 40 35 -90 3.68 0.5895
WVFGRD96 77.0 220 55 -90 3.68 0.5911
WVFGRD96 78.0 225 50 -85 3.69 0.5896
WVFGRD96 79.0 40 35 -85 3.70 0.5913
WVFGRD96 80.0 40 35 -85 3.70 0.5891
WVFGRD96 81.0 35 40 -100 3.69 0.5912
WVFGRD96 82.0 35 40 -100 3.70 0.5887
WVFGRD96 83.0 220 50 -90 3.70 0.5880
WVFGRD96 84.0 35 40 -100 3.70 0.5863
WVFGRD96 85.0 220 50 -90 3.71 0.5857
WVFGRD96 86.0 35 40 -100 3.70 0.5842
WVFGRD96 87.0 220 50 -90 3.71 0.5827
WVFGRD96 88.0 40 40 -90 3.71 0.5813
WVFGRD96 89.0 40 40 -90 3.71 0.5808
The best solution is
WVFGRD96 79.0 40 35 -85 3.70 0.5913
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
hp c 0.025 n 3 lp c 0.10 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