The ANSS event ID is ak0196rhyig7 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0196rhyig7/executive.
2019/05/27 23:44:49 60.246 -152.515 99.4 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/05/27 23:44:49:0 60.25 -152.51 99.4 4.2 Alaska
Stations used:
AK.BRLK AK.CAPN AK.CNP AK.CUT AK.GHO AK.HOM AK.KNK AK.PWL
AK.RC01 AK.SAW AK.SKN AK.SLK AK.SSN AK.SWD AT.PMR AV.ILSW
AV.STLK TA.L19K TA.M19K TA.M20K TA.M22K TA.N17K TA.N18K
TA.N19K TA.O18K TA.O19K TA.P18K TA.P19K TA.P23K TA.Q19K
TA.Q20K
Filtering commands used:
cut o DIST/3.3 -50 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.43e+22 dyne-cm
Mw = 4.29
Z = 94 km
Plane Strike Dip Rake
NP1 55 65 30
NP2 311 63 152
Principal Axes:
Axis Value Plunge Azimuth
T 3.43e+22 38 274
N 0.00e+00 52 91
P -3.43e+22 1 183
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.41e+22
Mxy -3.03e+21
Mxz 1.83e+21
Myy 2.10e+22
Myz -1.66e+22
Mzz 1.31e+22
--------------
----------------------
----------------------------
------------------------------
###########-----------------------
###############--------------------#
###################----------------###
#######################------------#####
#########################---------######
####### ##################-----#########
####### T ####################--##########
####### ####################-###########
############################-----#########
########################---------#######
######################------------######
##################---------------#####
############---------------------###
-##-----------------------------##
------------------------------
----------------------------
--------- ----------
----- P ------
Global CMT Convention Moment Tensor:
R T P
1.31e+22 1.83e+21 1.66e+22
1.83e+21 -3.41e+22 3.03e+21
1.66e+22 3.03e+21 2.10e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190527234449/index.html
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STK = 55
DIP = 65
RAKE = 30
MW = 4.29
HS = 94.0
The NDK file is 20190527234449.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 -50 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 115 55 -60 3.45 0.2192
WVFGRD96 4.0 325 65 15 3.46 0.2525
WVFGRD96 6.0 145 65 20 3.54 0.2852
WVFGRD96 8.0 145 65 20 3.62 0.3039
WVFGRD96 10.0 145 70 20 3.66 0.3055
WVFGRD96 12.0 145 70 15 3.69 0.2980
WVFGRD96 14.0 145 70 15 3.72 0.2838
WVFGRD96 16.0 145 70 15 3.74 0.2648
WVFGRD96 18.0 225 70 -25 3.77 0.2595
WVFGRD96 20.0 225 70 -20 3.79 0.2618
WVFGRD96 22.0 225 70 -20 3.82 0.2691
WVFGRD96 24.0 230 70 15 3.83 0.2798
WVFGRD96 26.0 230 70 15 3.86 0.2973
WVFGRD96 28.0 225 70 -10 3.89 0.3156
WVFGRD96 30.0 50 80 20 3.91 0.3332
WVFGRD96 32.0 50 80 20 3.93 0.3533
WVFGRD96 34.0 50 80 20 3.95 0.3707
WVFGRD96 36.0 50 80 20 3.98 0.3853
WVFGRD96 38.0 50 80 20 4.01 0.3984
WVFGRD96 40.0 55 70 30 4.08 0.4211
WVFGRD96 42.0 55 70 30 4.10 0.4239
WVFGRD96 44.0 55 75 30 4.12 0.4308
WVFGRD96 46.0 55 75 30 4.14 0.4417
WVFGRD96 48.0 55 75 30 4.16 0.4550
WVFGRD96 50.0 55 75 30 4.17 0.4672
WVFGRD96 52.0 55 70 30 4.19 0.4812
WVFGRD96 54.0 55 70 30 4.20 0.4921
WVFGRD96 56.0 55 70 30 4.21 0.5082
WVFGRD96 58.0 55 70 30 4.21 0.5208
WVFGRD96 60.0 55 70 30 4.22 0.5354
WVFGRD96 62.0 55 70 35 4.23 0.5476
WVFGRD96 64.0 55 70 35 4.24 0.5593
WVFGRD96 66.0 55 70 30 4.24 0.5693
WVFGRD96 68.0 55 70 30 4.25 0.5766
WVFGRD96 70.0 55 70 30 4.25 0.5851
WVFGRD96 72.0 55 70 30 4.26 0.5935
WVFGRD96 74.0 55 70 30 4.26 0.5997
WVFGRD96 76.0 55 65 30 4.26 0.6050
WVFGRD96 78.0 55 65 30 4.27 0.6097
WVFGRD96 80.0 55 65 30 4.27 0.6137
WVFGRD96 82.0 55 65 30 4.27 0.6156
WVFGRD96 84.0 55 65 30 4.28 0.6172
WVFGRD96 86.0 55 65 30 4.28 0.6188
WVFGRD96 88.0 55 65 30 4.28 0.6211
WVFGRD96 90.0 55 65 30 4.29 0.6234
WVFGRD96 92.0 55 65 30 4.29 0.6246
WVFGRD96 94.0 55 65 30 4.29 0.6252
WVFGRD96 96.0 55 65 30 4.30 0.6242
WVFGRD96 98.0 55 65 30 4.30 0.6234
WVFGRD96 100.0 55 65 30 4.30 0.6225
WVFGRD96 102.0 55 65 30 4.31 0.6222
WVFGRD96 104.0 55 65 30 4.31 0.6210
WVFGRD96 106.0 55 60 30 4.31 0.6197
WVFGRD96 108.0 55 60 30 4.31 0.6189
WVFGRD96 110.0 55 60 30 4.31 0.6168
WVFGRD96 112.0 55 60 30 4.32 0.6152
WVFGRD96 114.0 55 60 30 4.32 0.6143
WVFGRD96 116.0 55 60 30 4.32 0.6123
WVFGRD96 118.0 55 60 30 4.32 0.6075
WVFGRD96 120.0 55 60 30 4.33 0.6067
WVFGRD96 122.0 55 60 30 4.33 0.6049
WVFGRD96 124.0 55 60 30 4.33 0.6012
WVFGRD96 126.0 50 60 25 4.34 0.5995
WVFGRD96 128.0 50 60 25 4.34 0.5956
WVFGRD96 130.0 50 60 25 4.34 0.5939
WVFGRD96 132.0 50 60 25 4.35 0.5913
WVFGRD96 134.0 50 60 25 4.35 0.5888
WVFGRD96 136.0 50 60 25 4.35 0.5849
WVFGRD96 138.0 50 60 25 4.35 0.5823
WVFGRD96 140.0 50 60 25 4.36 0.5807
WVFGRD96 142.0 50 60 25 4.36 0.5752
WVFGRD96 144.0 50 60 25 4.36 0.5742
WVFGRD96 146.0 50 60 25 4.36 0.5699
WVFGRD96 148.0 50 60 25 4.36 0.5685
The best solution is
WVFGRD96 94.0 55 65 30 4.29 0.6252
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 -50 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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