The ANSS event ID is ak0193k3hc7 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0193k3hc7/executive.
2019/01/02 15:16:03 61.305 -149.950 41.3 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/01/02 15:16:03:0 61.31 -149.95 41.3 4.2 Alaska
Stations used:
AK.FID AK.FIRE AK.GHO AK.HIN AK.PWL AK.RC01 AK.SAW AK.SCM
AT.PMR GM.AD09 TA.M22K
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.72e+22 dyne-cm
Mw = 4.09
Z = 39 km
Plane Strike Dip Rake
NP1 185 70 -65
NP2 311 32 -139
Principal Axes:
Axis Value Plunge Azimuth
T 1.72e+22 21 256
N 0.00e+00 23 356
P -1.72e+22 58 129
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.11e+21
Mxy 5.85e+21
Mxz 3.51e+21
Myy 1.11e+22
Myz -1.17e+22
Mzz -1.00e+22
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###############----------------#######
################-----------------#######
###############-------------------######
################--------------------######
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################----------------------####
### ##########---------- ---------####
## T ##########---------- P ---------###
## ##########---------- ---------###
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Global CMT Convention Moment Tensor:
R T P
-1.00e+22 3.51e+21 1.17e+22
3.51e+21 -1.11e+21 -5.85e+21
1.17e+22 -5.85e+21 1.11e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190102151603/index.html
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STK = 185
DIP = 70
RAKE = -65
MW = 4.09
HS = 39.0
The NDK file is 20190102151603.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 o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 105 90 -10 3.41 0.2046
WVFGRD96 2.0 105 85 -5 3.58 0.3116
WVFGRD96 3.0 250 75 35 3.63 0.3459
WVFGRD96 4.0 300 65 25 3.70 0.3841
WVFGRD96 5.0 130 90 -50 3.73 0.4245
WVFGRD96 6.0 55 45 5 3.73 0.4557
WVFGRD96 7.0 55 50 10 3.74 0.4746
WVFGRD96 8.0 55 40 5 3.79 0.4841
WVFGRD96 9.0 60 45 15 3.79 0.4956
WVFGRD96 10.0 60 50 20 3.81 0.5031
WVFGRD96 11.0 60 50 20 3.81 0.5088
WVFGRD96 12.0 60 50 20 3.82 0.5118
WVFGRD96 13.0 60 50 20 3.83 0.5119
WVFGRD96 14.0 60 50 20 3.84 0.5110
WVFGRD96 15.0 55 55 5 3.84 0.5096
WVFGRD96 16.0 55 55 5 3.85 0.5085
WVFGRD96 17.0 55 55 5 3.86 0.5080
WVFGRD96 18.0 55 55 5 3.87 0.5063
WVFGRD96 19.0 55 55 5 3.88 0.5064
WVFGRD96 20.0 50 55 0 3.88 0.5065
WVFGRD96 21.0 50 55 0 3.90 0.5061
WVFGRD96 22.0 50 55 0 3.91 0.5062
WVFGRD96 23.0 50 55 -5 3.92 0.5041
WVFGRD96 24.0 50 55 -5 3.92 0.5024
WVFGRD96 25.0 50 55 -5 3.93 0.5003
WVFGRD96 26.0 50 55 -5 3.94 0.5002
WVFGRD96 27.0 50 55 -15 3.95 0.5054
WVFGRD96 28.0 50 55 -15 3.96 0.5099
WVFGRD96 29.0 50 55 -15 3.97 0.5114
WVFGRD96 30.0 50 55 -25 3.98 0.5109
WVFGRD96 31.0 190 80 -80 4.04 0.5156
WVFGRD96 32.0 190 80 -80 4.05 0.5273
WVFGRD96 33.0 190 80 -80 4.05 0.5384
WVFGRD96 34.0 190 80 -80 4.06 0.5483
WVFGRD96 35.0 190 80 -80 4.06 0.5575
WVFGRD96 36.0 190 80 -80 4.07 0.5654
WVFGRD96 37.0 190 80 -80 4.07 0.5731
WVFGRD96 38.0 190 80 -80 4.07 0.5795
WVFGRD96 39.0 185 70 -65 4.09 0.5910
WVFGRD96 40.0 -10 10 -110 4.21 0.5801
WVFGRD96 41.0 190 80 -85 4.21 0.5766
WVFGRD96 42.0 185 70 -75 4.21 0.5754
WVFGRD96 43.0 185 70 -75 4.22 0.5780
WVFGRD96 44.0 185 70 -75 4.22 0.5809
WVFGRD96 45.0 185 70 -75 4.23 0.5834
WVFGRD96 46.0 185 70 -75 4.24 0.5848
WVFGRD96 47.0 185 70 -75 4.24 0.5861
WVFGRD96 48.0 185 70 -75 4.25 0.5864
WVFGRD96 49.0 185 70 -75 4.25 0.5863
WVFGRD96 50.0 185 70 -75 4.26 0.5861
WVFGRD96 51.0 180 70 -75 4.27 0.5843
WVFGRD96 52.0 185 70 -75 4.26 0.5832
WVFGRD96 53.0 180 70 -75 4.27 0.5813
WVFGRD96 54.0 180 70 -75 4.28 0.5785
WVFGRD96 55.0 180 70 -75 4.28 0.5763
WVFGRD96 56.0 180 70 -75 4.28 0.5723
WVFGRD96 57.0 90 25 -10 4.31 0.5721
WVFGRD96 58.0 90 25 -10 4.31 0.5737
WVFGRD96 59.0 95 25 -5 4.32 0.5744
The best solution is
WVFGRD96 39.0 185 70 -65 4.09 0.5910
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 o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2
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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