The ANSS event ID is ak012gi080jr and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak012gi080jr/executive.
2012/12/24 17:28:25 61.243 -150.764 64.4 4.4 Alaska
USGS/SLU Moment Tensor Solution
ENS 2012/12/24 17:28:25:0 61.24 -150.76 64.4 4.4 Alaska
Stations used:
AK.GHO AK.KNK AK.PPLA AK.SAW AK.SCM AK.SKN AK.SSN AK.SWD
AT.PMR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.43e+22 dyne-cm
Mw = 4.19
Z = 70 km
Plane Strike Dip Rake
NP1 188 82 -114
NP2 80 25 -20
Principal Axes:
Axis Value Plunge Azimuth
T 2.43e+22 33 298
N 0.00e+00 23 192
P -2.43e+22 48 73
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.87e+21
Mxy -1.01e+22
Mxz 1.67e+21
Myy 3.49e+21
Myz -2.13e+22
Mzz -6.36e+21
#########-----
#############---------
###############-------------
################--------------
#################-----------------
##################------------------
##### ##########--------------------
###### T ##########---------------------
###### ##########--------- ---------
###################---------- P ---------#
###################---------- ---------#
###################----------------------#
##################----------------------##
#################---------------------##
-################--------------------###
-###############-------------------###
--#############-----------------####
---###########--------------######
-----#######-----------#######
----------#----#############
--------##############
----##########
Global CMT Convention Moment Tensor:
R T P
-6.36e+21 1.67e+21 2.13e+22
1.67e+21 2.87e+21 1.01e+22
2.13e+22 1.01e+22 3.49e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121224172825/index.html
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STK = 80
DIP = 25
RAKE = -20
MW = 4.19
HS = 70.0
The NDK file is 20121224172825.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 0.02 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 35 40 -90 3.23 0.2152
WVFGRD96 1.0 30 80 10 3.22 0.2190
WVFGRD96 2.0 5 75 -15 3.30 0.2817
WVFGRD96 3.0 25 90 5 3.45 0.3114
WVFGRD96 4.0 205 85 -10 3.51 0.3144
WVFGRD96 5.0 190 60 20 3.46 0.3323
WVFGRD96 6.0 190 60 20 3.50 0.3575
WVFGRD96 7.0 10 60 15 3.54 0.3818
WVFGRD96 8.0 10 55 20 3.59 0.4057
WVFGRD96 9.0 190 80 30 3.62 0.4172
WVFGRD96 10.0 185 90 30 3.63 0.4307
WVFGRD96 11.0 185 90 25 3.66 0.4386
WVFGRD96 12.0 185 85 25 3.67 0.4419
WVFGRD96 13.0 185 85 25 3.69 0.4422
WVFGRD96 14.0 185 85 25 3.71 0.4416
WVFGRD96 15.0 185 70 20 3.71 0.4366
WVFGRD96 16.0 185 75 20 3.73 0.4323
WVFGRD96 17.0 185 75 20 3.74 0.4261
WVFGRD96 18.0 185 75 20 3.76 0.4176
WVFGRD96 19.0 190 70 20 3.78 0.4096
WVFGRD96 20.0 190 70 20 3.79 0.4001
WVFGRD96 21.0 190 70 20 3.80 0.3906
WVFGRD96 22.0 190 70 15 3.81 0.3800
WVFGRD96 23.0 190 70 15 3.82 0.3659
WVFGRD96 24.0 190 70 15 3.82 0.3550
WVFGRD96 25.0 190 65 15 3.83 0.3436
WVFGRD96 26.0 30 85 10 3.87 0.3460
WVFGRD96 27.0 35 85 20 3.87 0.3561
WVFGRD96 28.0 35 85 20 3.88 0.3651
WVFGRD96 29.0 35 85 20 3.89 0.3717
WVFGRD96 30.0 35 85 25 3.89 0.3796
WVFGRD96 31.0 45 70 25 3.90 0.3884
WVFGRD96 32.0 45 70 25 3.91 0.3989
WVFGRD96 33.0 45 70 25 3.92 0.4078
WVFGRD96 34.0 45 70 25 3.93 0.4181
WVFGRD96 35.0 45 70 25 3.94 0.4289
WVFGRD96 36.0 45 70 25 3.95 0.4389
WVFGRD96 37.0 45 85 40 3.96 0.4479
WVFGRD96 38.0 45 85 40 3.96 0.4585
WVFGRD96 39.0 50 80 40 3.97 0.4669
WVFGRD96 40.0 45 85 55 4.06 0.4679
WVFGRD96 41.0 45 85 55 4.07 0.4760
WVFGRD96 42.0 45 85 55 4.08 0.4787
WVFGRD96 43.0 45 80 50 4.08 0.4858
WVFGRD96 44.0 50 75 45 4.09 0.4905
WVFGRD96 45.0 50 75 45 4.10 0.4963
WVFGRD96 46.0 65 25 -30 4.09 0.5050
WVFGRD96 47.0 65 25 -30 4.09 0.5148
WVFGRD96 48.0 70 25 -30 4.10 0.5234
WVFGRD96 49.0 70 25 -30 4.11 0.5338
WVFGRD96 50.0 70 25 -30 4.12 0.5439
WVFGRD96 51.0 70 25 -30 4.12 0.5519
WVFGRD96 52.0 70 25 -30 4.13 0.5595
WVFGRD96 53.0 70 25 -30 4.13 0.5683
WVFGRD96 54.0 75 25 -25 4.13 0.5747
WVFGRD96 55.0 75 25 -25 4.14 0.5799
WVFGRD96 56.0 75 25 -25 4.14 0.5876
WVFGRD96 57.0 75 25 -25 4.15 0.5945
WVFGRD96 58.0 75 25 -25 4.15 0.5989
WVFGRD96 59.0 75 25 -25 4.15 0.6011
WVFGRD96 60.0 75 25 -25 4.16 0.6070
WVFGRD96 61.0 75 25 -25 4.16 0.6109
WVFGRD96 62.0 75 25 -25 4.16 0.6131
WVFGRD96 63.0 75 25 -25 4.17 0.6148
WVFGRD96 64.0 80 25 -20 4.17 0.6191
WVFGRD96 65.0 80 25 -20 4.17 0.6206
WVFGRD96 66.0 80 25 -20 4.17 0.6217
WVFGRD96 67.0 80 25 -20 4.18 0.6232
WVFGRD96 68.0 80 25 -20 4.18 0.6235
WVFGRD96 69.0 80 25 -20 4.18 0.6255
WVFGRD96 70.0 80 25 -20 4.19 0.6257
WVFGRD96 71.0 85 25 -15 4.18 0.6240
WVFGRD96 72.0 85 25 -15 4.19 0.6243
WVFGRD96 73.0 85 25 -15 4.19 0.6247
WVFGRD96 74.0 85 25 -15 4.19 0.6247
WVFGRD96 75.0 90 25 -15 4.20 0.6249
WVFGRD96 76.0 90 25 -15 4.20 0.6217
WVFGRD96 77.0 90 25 -15 4.21 0.6211
WVFGRD96 78.0 90 20 -15 4.20 0.6208
WVFGRD96 79.0 90 20 -15 4.21 0.6215
WVFGRD96 80.0 95 25 -10 4.21 0.6189
WVFGRD96 81.0 95 20 -10 4.21 0.6175
WVFGRD96 82.0 95 20 -10 4.21 0.6151
WVFGRD96 83.0 95 20 -10 4.22 0.6153
WVFGRD96 84.0 95 20 -10 4.22 0.6147
WVFGRD96 85.0 95 20 -10 4.22 0.6123
WVFGRD96 86.0 100 25 -5 4.22 0.6102
WVFGRD96 87.0 100 25 -5 4.23 0.6072
WVFGRD96 88.0 100 25 -5 4.23 0.6066
WVFGRD96 89.0 100 25 -5 4.23 0.6061
WVFGRD96 90.0 105 25 -5 4.24 0.6037
WVFGRD96 91.0 105 25 -5 4.24 0.6019
WVFGRD96 92.0 105 25 -5 4.25 0.5978
WVFGRD96 93.0 105 25 -5 4.25 0.5966
WVFGRD96 94.0 110 25 0 4.25 0.5954
WVFGRD96 95.0 110 25 0 4.25 0.5946
WVFGRD96 96.0 110 25 0 4.25 0.5928
WVFGRD96 97.0 110 25 0 4.26 0.5907
WVFGRD96 98.0 110 25 0 4.26 0.5874
WVFGRD96 99.0 110 25 0 4.26 0.5872
The best solution is
WVFGRD96 70.0 80 25 -20 4.19 0.6257
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 0.02 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