The ANSS event ID is ak0196dzvlpi and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0196dzvlpi/executive.
2019/05/19 07:01:54 61.320 -149.956 46.3 4.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/05/19 07:01:54:0 61.32 -149.96 46.3 4.1 Alaska
Stations used:
AK.BMR AK.CAPN AK.CUT AK.DIV AK.FID AK.GHO AK.GLI AK.HDA
AK.HOM AK.KNK AK.PPLA AK.PWL AK.RC01 AK.SAW AK.SKN AK.SLK
AK.SSN AK.SWD AT.PMR AT.TTA AV.ILSW AV.STLK TA.L19K TA.M19K
TA.M22K TA.N19K TA.O18K TA.O22K TA.P19K
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 = 1.55e+22 dyne-cm
Mw = 4.06
Z = 45 km
Plane Strike Dip Rake
NP1 333 57 -130
NP2 210 50 -45
Principal Axes:
Axis Value Plunge Azimuth
T 1.55e+22 4 90
N 0.00e+00 33 357
P -1.55e+22 57 186
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.57e+21
Mxy -4.75e+20
Mxz 7.05e+21
Myy 1.54e+22
Myz 1.87e+21
Mzz -1.08e+22
--------------
#####-------------####
###########-----############
##############-###############
##############-----###############
#############--------###############
#############-----------##############
############--------------##############
###########----------------#############
###########------------------##########
##########--------------------######### T
##########--------------------#########
#########----------------------###########
########----------------------##########
########---------- ----------#########
######----------- P ----------########
#####----------- ----------#######
#####-----------------------######
###-----------------------####
###---------------------####
---------------------#
--------------
Global CMT Convention Moment Tensor:
R T P
-1.08e+22 7.05e+21 -1.87e+21
7.05e+21 -4.57e+21 4.75e+20
-1.87e+21 4.75e+20 1.54e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190519070154/index.html
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STK = 210
DIP = 50
RAKE = -45
MW = 4.06
HS = 45.0
The NDK file is 20190519070154.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 1.0 340 50 65 3.21 0.1910
WVFGRD96 2.0 350 45 80 3.39 0.2646
WVFGRD96 3.0 125 65 -25 3.35 0.2512
WVFGRD96 4.0 125 65 -30 3.40 0.2829
WVFGRD96 5.0 125 65 -30 3.44 0.3029
WVFGRD96 6.0 130 70 -30 3.46 0.3179
WVFGRD96 7.0 130 70 -30 3.49 0.3309
WVFGRD96 8.0 130 70 -35 3.55 0.3354
WVFGRD96 9.0 130 70 -40 3.57 0.3412
WVFGRD96 10.0 130 70 -40 3.59 0.3446
WVFGRD96 11.0 130 70 -40 3.61 0.3455
WVFGRD96 12.0 50 60 30 3.63 0.3505
WVFGRD96 13.0 40 65 30 3.64 0.3545
WVFGRD96 14.0 40 70 30 3.65 0.3578
WVFGRD96 15.0 40 70 30 3.67 0.3601
WVFGRD96 16.0 40 70 30 3.68 0.3609
WVFGRD96 17.0 40 70 30 3.69 0.3604
WVFGRD96 18.0 210 85 -40 3.70 0.3624
WVFGRD96 19.0 230 60 20 3.72 0.3650
WVFGRD96 20.0 230 60 15 3.73 0.3692
WVFGRD96 21.0 230 60 15 3.75 0.3738
WVFGRD96 22.0 220 65 -25 3.76 0.3850
WVFGRD96 23.0 220 65 -25 3.77 0.3942
WVFGRD96 24.0 220 65 -30 3.78 0.4045
WVFGRD96 25.0 220 65 -30 3.79 0.4146
WVFGRD96 26.0 220 65 -30 3.80 0.4237
WVFGRD96 27.0 220 65 -25 3.81 0.4318
WVFGRD96 28.0 220 55 -15 3.83 0.4454
WVFGRD96 29.0 220 55 -20 3.84 0.4632
WVFGRD96 30.0 220 55 -20 3.85 0.4796
WVFGRD96 31.0 220 55 -20 3.86 0.4934
WVFGRD96 32.0 220 55 -20 3.87 0.5069
WVFGRD96 33.0 215 55 -35 3.88 0.5220
WVFGRD96 34.0 215 55 -35 3.89 0.5415
WVFGRD96 35.0 215 55 -40 3.90 0.5574
WVFGRD96 36.0 215 55 -40 3.91 0.5699
WVFGRD96 37.0 215 55 -40 3.91 0.5790
WVFGRD96 38.0 215 55 -40 3.92 0.5859
WVFGRD96 39.0 215 55 -40 3.94 0.5921
WVFGRD96 40.0 210 50 -45 4.01 0.5933
WVFGRD96 41.0 210 50 -45 4.02 0.6026
WVFGRD96 42.0 210 50 -45 4.03 0.6082
WVFGRD96 43.0 210 50 -45 4.04 0.6119
WVFGRD96 44.0 210 50 -45 4.05 0.6133
WVFGRD96 45.0 210 50 -45 4.06 0.6155
WVFGRD96 46.0 210 50 -45 4.06 0.6128
WVFGRD96 47.0 210 50 -45 4.07 0.6133
WVFGRD96 48.0 210 50 -45 4.07 0.6098
WVFGRD96 49.0 210 50 -45 4.08 0.6080
WVFGRD96 50.0 210 50 -45 4.08 0.6045
WVFGRD96 51.0 210 50 -45 4.08 0.6021
WVFGRD96 52.0 210 50 -45 4.09 0.5989
WVFGRD96 53.0 210 50 -45 4.09 0.5953
WVFGRD96 54.0 210 50 -45 4.09 0.5921
WVFGRD96 55.0 215 55 -40 4.09 0.5893
WVFGRD96 56.0 215 55 -40 4.10 0.5865
WVFGRD96 57.0 215 55 -40 4.10 0.5823
WVFGRD96 58.0 215 55 -40 4.10 0.5787
WVFGRD96 59.0 215 55 -40 4.10 0.5758
WVFGRD96 60.0 215 55 -40 4.11 0.5719
WVFGRD96 61.0 215 55 -40 4.11 0.5670
WVFGRD96 62.0 215 55 -40 4.11 0.5644
WVFGRD96 63.0 215 55 -40 4.11 0.5595
WVFGRD96 64.0 215 55 -40 4.11 0.5560
WVFGRD96 65.0 215 55 -40 4.12 0.5513
WVFGRD96 66.0 215 55 -40 4.12 0.5478
WVFGRD96 67.0 215 50 -40 4.12 0.5448
WVFGRD96 68.0 215 50 -40 4.12 0.5406
WVFGRD96 69.0 215 50 -40 4.12 0.5377
WVFGRD96 70.0 215 50 -40 4.12 0.5351
WVFGRD96 71.0 215 50 -40 4.12 0.5307
WVFGRD96 72.0 215 50 -40 4.13 0.5280
WVFGRD96 73.0 215 50 -40 4.13 0.5244
WVFGRD96 74.0 215 50 -40 4.13 0.5209
WVFGRD96 75.0 215 50 -40 4.13 0.5167
WVFGRD96 76.0 215 50 -40 4.13 0.5135
WVFGRD96 77.0 215 50 -40 4.13 0.5098
WVFGRD96 78.0 215 50 -40 4.13 0.5049
WVFGRD96 79.0 215 50 -40 4.13 0.5012
The best solution is
WVFGRD96 45.0 210 50 -45 4.06 0.6155
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