The ANSS event ID is ak0195zdvbuz and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0195zdvbuz/executive.
2019/05/10 23:52:45 60.274 -150.933 51.4 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/05/10 23:52:45:0 60.27 -150.93 51.4 4.2 Alaska
Stations used:
AK.BRLK AK.CAPN AK.CNP AK.DIV AK.KNK AK.PPLA AK.PWL AK.RC01
AK.SKN AK.SLK AK.SSN AK.SWD AT.PMR AV.ILSW AV.RED AV.STLK
TA.M19K TA.M20K TA.M22K TA.N18K TA.O18K TA.O19K TA.O22K
TA.P18K TA.P19K TA.Q19K
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +40
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 5.37e+22 dyne-cm
Mw = 4.42
Z = 60 km
Plane Strike Dip Rake
NP1 163 81 -160
NP2 70 70 -10
Principal Axes:
Axis Value Plunge Azimuth
T 5.37e+22 7 295
N 0.00e+00 68 187
P -5.37e+22 21 28
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.67e+22
Mxy -4.00e+22
Mxz -1.29e+22
Myy 3.26e+22
Myz -1.46e+22
Mzz -5.99e+21
#-------------
#####-----------------
########------------ -----
#########------------ P ------
############----------- --------
###########-----------------------
T ###########------------------------
# ############-----------------------#
################---------------------###
##################------------------######
##################----------------########
###################------------###########
###################---------##############
###################---##################
################----####################
-------------------###################
-------------------#################
-------------------###############
------------------############
-----------------###########
---------------#######
-------------#
Global CMT Convention Moment Tensor:
R T P
-5.99e+21 -1.29e+22 1.46e+22
-1.29e+22 -2.67e+22 4.00e+22
1.46e+22 4.00e+22 3.26e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190510235245/index.html
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STK = 70
DIP = 70
RAKE = -10
MW = 4.42
HS = 60.0
The NDK file is 20190510235245.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 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 165 80 5 3.46 0.2071
WVFGRD96 2.0 165 75 0 3.59 0.2766
WVFGRD96 3.0 170 70 15 3.65 0.2984
WVFGRD96 4.0 165 90 20 3.68 0.3133
WVFGRD96 5.0 345 80 -20 3.72 0.3245
WVFGRD96 6.0 170 80 30 3.76 0.3328
WVFGRD96 7.0 260 70 15 3.79 0.3526
WVFGRD96 8.0 260 70 20 3.84 0.3758
WVFGRD96 9.0 260 70 20 3.86 0.3895
WVFGRD96 10.0 260 70 15 3.88 0.3998
WVFGRD96 11.0 260 75 20 3.90 0.4084
WVFGRD96 12.0 255 80 15 3.91 0.4162
WVFGRD96 13.0 255 85 20 3.94 0.4242
WVFGRD96 14.0 75 80 -15 3.95 0.4345
WVFGRD96 15.0 75 80 -15 3.97 0.4417
WVFGRD96 16.0 75 80 -15 3.98 0.4481
WVFGRD96 17.0 75 80 -10 3.99 0.4538
WVFGRD96 18.0 75 80 -10 4.00 0.4593
WVFGRD96 19.0 75 80 -5 4.01 0.4649
WVFGRD96 20.0 75 80 -5 4.02 0.4705
WVFGRD96 21.0 75 75 -5 4.04 0.4766
WVFGRD96 22.0 75 75 -5 4.05 0.4826
WVFGRD96 23.0 75 75 -5 4.06 0.4890
WVFGRD96 24.0 75 75 -5 4.07 0.4958
WVFGRD96 25.0 75 75 -10 4.08 0.5023
WVFGRD96 26.0 75 75 -5 4.09 0.5083
WVFGRD96 27.0 75 75 -5 4.09 0.5147
WVFGRD96 28.0 75 75 -5 4.10 0.5208
WVFGRD96 29.0 70 70 -20 4.14 0.5265
WVFGRD96 30.0 70 70 -20 4.15 0.5324
WVFGRD96 31.0 70 70 -20 4.16 0.5387
WVFGRD96 32.0 70 70 -20 4.17 0.5452
WVFGRD96 33.0 70 70 -20 4.18 0.5509
WVFGRD96 34.0 70 70 -20 4.19 0.5572
WVFGRD96 35.0 70 70 -20 4.20 0.5612
WVFGRD96 36.0 70 70 -20 4.21 0.5657
WVFGRD96 37.0 70 70 -15 4.22 0.5711
WVFGRD96 38.0 70 70 -10 4.23 0.5754
WVFGRD96 39.0 70 70 -10 4.24 0.5815
WVFGRD96 40.0 70 60 -15 4.29 0.5867
WVFGRD96 41.0 70 60 -10 4.30 0.5921
WVFGRD96 42.0 70 60 -10 4.31 0.5968
WVFGRD96 43.0 70 60 -15 4.32 0.6019
WVFGRD96 44.0 70 60 -15 4.33 0.6044
WVFGRD96 45.0 70 60 -15 4.34 0.6080
WVFGRD96 46.0 70 65 -15 4.35 0.6111
WVFGRD96 47.0 70 65 -15 4.35 0.6135
WVFGRD96 48.0 70 65 -15 4.36 0.6168
WVFGRD96 49.0 70 65 -15 4.37 0.6185
WVFGRD96 50.0 70 65 -15 4.38 0.6202
WVFGRD96 51.0 70 65 -15 4.38 0.6229
WVFGRD96 52.0 70 65 -15 4.39 0.6237
WVFGRD96 53.0 70 65 -15 4.40 0.6252
WVFGRD96 54.0 70 65 -15 4.40 0.6260
WVFGRD96 55.0 70 65 -15 4.41 0.6256
WVFGRD96 56.0 70 70 -15 4.41 0.6269
WVFGRD96 57.0 70 70 -10 4.41 0.6269
WVFGRD96 58.0 70 70 -10 4.41 0.6272
WVFGRD96 59.0 70 70 -10 4.42 0.6271
WVFGRD96 60.0 70 70 -10 4.42 0.6273
WVFGRD96 61.0 70 70 -10 4.43 0.6263
WVFGRD96 62.0 70 70 -10 4.43 0.6271
WVFGRD96 63.0 70 70 -10 4.43 0.6258
WVFGRD96 64.0 70 70 -10 4.44 0.6254
WVFGRD96 65.0 70 70 -10 4.44 0.6245
WVFGRD96 66.0 70 75 -10 4.44 0.6236
WVFGRD96 67.0 70 75 -10 4.45 0.6235
WVFGRD96 68.0 70 75 -10 4.45 0.6221
WVFGRD96 69.0 70 75 -10 4.45 0.6214
WVFGRD96 70.0 70 75 -10 4.46 0.6194
WVFGRD96 71.0 70 75 -10 4.46 0.6193
WVFGRD96 72.0 70 75 -10 4.46 0.6173
WVFGRD96 73.0 70 75 -5 4.46 0.6162
WVFGRD96 74.0 70 75 -5 4.46 0.6149
WVFGRD96 75.0 70 75 -5 4.46 0.6132
WVFGRD96 76.0 70 75 -5 4.46 0.6123
WVFGRD96 77.0 70 75 -5 4.47 0.6107
WVFGRD96 78.0 70 75 -5 4.47 0.6078
WVFGRD96 79.0 70 75 -5 4.47 0.6076
WVFGRD96 80.0 70 75 -5 4.47 0.6050
WVFGRD96 81.0 75 75 0 4.46 0.6026
WVFGRD96 82.0 75 75 0 4.46 0.6024
WVFGRD96 83.0 75 75 0 4.47 0.6001
WVFGRD96 84.0 75 75 0 4.47 0.5987
WVFGRD96 85.0 75 80 0 4.47 0.5975
WVFGRD96 86.0 75 80 0 4.47 0.5956
WVFGRD96 87.0 75 80 0 4.47 0.5944
WVFGRD96 88.0 75 80 0 4.48 0.5926
WVFGRD96 89.0 75 80 0 4.48 0.5907
WVFGRD96 90.0 75 80 0 4.48 0.5895
WVFGRD96 91.0 75 80 0 4.48 0.5872
WVFGRD96 92.0 75 80 5 4.48 0.5863
WVFGRD96 93.0 75 80 5 4.48 0.5841
WVFGRD96 94.0 75 80 5 4.48 0.5831
WVFGRD96 95.0 75 80 5 4.48 0.5825
WVFGRD96 96.0 75 80 5 4.49 0.5796
WVFGRD96 97.0 75 80 5 4.49 0.5787
WVFGRD96 98.0 75 80 5 4.49 0.5781
WVFGRD96 99.0 75 80 5 4.49 0.5759
The best solution is
WVFGRD96 60.0 70 70 -10 4.42 0.6273
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 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 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