The ANSS event ID is ak019edz87xd and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak019edz87xd/executive.
2019/11/09 20:18:31 60.031 -153.400 146.3 3.9 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/11/09 20:18:31:0 60.03 -153.40 146.3 3.9 Alaska
Stations used:
AK.CNP AK.HOM AK.L19K AK.N19K AK.PPLA AK.Q19K AK.RC01
AK.SKN AK.SSN AV.ACH AV.ILSW AV.STLK II.KDAK TA.M22K
TA.O19K TA.P19K TA.Q20K
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
Best Fitting Double Couple
Mo = 1.17e+22 dyne-cm
Mw = 3.98
Z = 168 km
Plane Strike Dip Rake
NP1 310 67 136
NP2 60 50 30
Principal Axes:
Axis Value Plunge Azimuth
T 1.17e+22 46 267
N 0.00e+00 42 108
P -1.17e+22 11 9
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.11e+22
Mxy -1.39e+21
Mxz -2.39e+21
Myy 5.30e+21
Myz -6.17e+21
Mzz 5.79e+21
-------- P ---
------------ -------
----------------------------
------------------------------
########--------------------------
#############-----------------------
#################--------------------#
#####################----------------###
#######################--------------###
###########################----------#####
######### ################--------######
######### T ##################-----#######
######### ####################-#########
###############################-########
############################-----#######
#########################--------#####
####################-------------###
---###########-------------------#
------------------------------
----------------------------
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Global CMT Convention Moment Tensor:
R T P
5.79e+21 -2.39e+21 6.17e+21
-2.39e+21 -1.11e+22 1.39e+21
6.17e+21 1.39e+21 5.30e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20191109201831/index.html
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STK = 60
DIP = 50
RAKE = 30
MW = 3.98
HS = 168.0
The NDK file is 20191109201831.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 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 290 65 15 2.93 0.1446
WVFGRD96 4.0 300 70 45 3.08 0.1647
WVFGRD96 6.0 295 70 35 3.13 0.1834
WVFGRD96 8.0 300 75 45 3.23 0.1944
WVFGRD96 10.0 300 75 40 3.26 0.1978
WVFGRD96 12.0 295 80 35 3.29 0.1952
WVFGRD96 14.0 295 80 35 3.32 0.1886
WVFGRD96 16.0 295 80 35 3.34 0.1796
WVFGRD96 18.0 200 50 -5 3.37 0.1812
WVFGRD96 20.0 200 50 -5 3.40 0.1888
WVFGRD96 22.0 200 50 -10 3.44 0.1984
WVFGRD96 24.0 205 50 -5 3.46 0.2073
WVFGRD96 26.0 205 55 -10 3.48 0.2146
WVFGRD96 28.0 210 55 -5 3.50 0.2206
WVFGRD96 30.0 210 60 -5 3.51 0.2269
WVFGRD96 32.0 210 60 -5 3.53 0.2260
WVFGRD96 34.0 210 65 -5 3.54 0.2225
WVFGRD96 36.0 215 65 0 3.56 0.2191
WVFGRD96 38.0 215 70 0 3.59 0.2143
WVFGRD96 40.0 215 65 0 3.65 0.2087
WVFGRD96 42.0 215 65 0 3.67 0.2050
WVFGRD96 44.0 215 65 -5 3.70 0.2002
WVFGRD96 46.0 220 65 0 3.73 0.1979
WVFGRD96 48.0 220 65 0 3.75 0.1985
WVFGRD96 50.0 220 65 0 3.76 0.1997
WVFGRD96 52.0 220 70 0 3.77 0.2054
WVFGRD96 54.0 225 70 5 3.80 0.2137
WVFGRD96 56.0 225 70 5 3.82 0.2267
WVFGRD96 58.0 225 70 5 3.84 0.2402
WVFGRD96 60.0 225 75 5 3.84 0.2533
WVFGRD96 62.0 225 75 5 3.86 0.2667
WVFGRD96 64.0 225 75 5 3.87 0.2779
WVFGRD96 66.0 225 70 10 3.88 0.2856
WVFGRD96 68.0 225 70 10 3.88 0.2940
WVFGRD96 70.0 225 70 10 3.89 0.2987
WVFGRD96 72.0 225 70 10 3.90 0.3074
WVFGRD96 74.0 225 70 15 3.89 0.3165
WVFGRD96 76.0 225 70 15 3.90 0.3264
WVFGRD96 78.0 225 70 15 3.91 0.3329
WVFGRD96 80.0 225 70 15 3.91 0.3371
WVFGRD96 82.0 225 70 15 3.91 0.3399
WVFGRD96 84.0 225 70 15 3.92 0.3408
WVFGRD96 86.0 225 70 15 3.92 0.3413
WVFGRD96 88.0 225 70 15 3.92 0.3421
WVFGRD96 90.0 45 65 40 3.86 0.3486
WVFGRD96 92.0 60 60 40 3.89 0.3902
WVFGRD96 94.0 60 60 40 3.91 0.4336
WVFGRD96 96.0 60 60 35 3.91 0.4632
WVFGRD96 98.0 60 60 35 3.92 0.4815
WVFGRD96 100.0 60 60 35 3.93 0.4967
WVFGRD96 102.0 60 60 35 3.93 0.5020
WVFGRD96 104.0 60 60 35 3.93 0.5060
WVFGRD96 106.0 60 60 35 3.93 0.5070
WVFGRD96 108.0 60 60 35 3.94 0.5116
WVFGRD96 110.0 60 60 35 3.94 0.5130
WVFGRD96 112.0 60 55 30 3.93 0.5162
WVFGRD96 114.0 60 55 30 3.93 0.5172
WVFGRD96 116.0 60 55 30 3.93 0.5196
WVFGRD96 118.0 60 55 30 3.93 0.5202
WVFGRD96 120.0 60 55 30 3.93 0.5220
WVFGRD96 122.0 60 55 30 3.94 0.5238
WVFGRD96 124.0 60 55 30 3.94 0.5251
WVFGRD96 126.0 60 55 30 3.94 0.5261
WVFGRD96 128.0 60 55 30 3.94 0.5251
WVFGRD96 130.0 60 55 30 3.95 0.5266
WVFGRD96 132.0 60 55 30 3.95 0.5262
WVFGRD96 134.0 60 55 30 3.95 0.5269
WVFGRD96 136.0 60 55 30 3.95 0.5256
WVFGRD96 138.0 60 55 30 3.95 0.5261
WVFGRD96 140.0 60 55 30 3.96 0.5270
WVFGRD96 142.0 60 55 30 3.96 0.5249
WVFGRD96 144.0 60 55 30 3.96 0.5253
WVFGRD96 146.0 60 55 30 3.96 0.5249
WVFGRD96 148.0 60 50 30 3.95 0.5246
WVFGRD96 150.0 60 50 30 3.96 0.5257
WVFGRD96 152.0 60 50 30 3.96 0.5253
WVFGRD96 154.0 60 50 30 3.96 0.5253
WVFGRD96 156.0 60 50 30 3.96 0.5264
WVFGRD96 158.0 60 50 30 3.97 0.5264
WVFGRD96 160.0 60 50 30 3.97 0.5261
WVFGRD96 162.0 60 50 30 3.97 0.5262
WVFGRD96 164.0 60 50 30 3.97 0.5270
WVFGRD96 166.0 60 50 30 3.97 0.5270
WVFGRD96 168.0 60 50 30 3.98 0.5270
The best solution is
WVFGRD96 168.0 60 50 30 3.98 0.5270
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
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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