Left: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated. Right: residuals as a function of distance and azimuth.
The ANSS event ID is ak0194tvwxby and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0194tvwxby/executive.
2019/04/15 14:25:27 60.649 -141.512 14.6 3.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/04/15 14:25:27:0 60.65 -141.51 14.6 3.8 Alaska
Stations used:
AK.BAL AK.BARK AK.BCP AK.BGLC AK.CYK AK.DIV AK.DOT AK.FID
AK.GLB AK.GRIN AK.KIAG AK.KNK AK.MESA AK.NICH AK.PAX
AK.RIDG AK.RKAV AK.SAMH AK.SCRK AK.SSP AK.VRDI AK.YAH
AT.MENT AV.WACK AV.WAZA CN.BRWY CN.BVCY CN.HYT CN.YUK2
CN.YUK6 CN.YUK7 CN.YUK8 TA.K24K TA.K27K TA.L27K TA.L29M
TA.M26K TA.M27K TA.M29M TA.M30M TA.N31M TA.O28M TA.O29M
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
Best Fitting Double Couple
Mo = 1.10e+22 dyne-cm
Mw = 3.96
Z = 26 km
Plane Strike Dip Rake
NP1 269 77 -98
NP2 120 15 -60
Principal Axes:
Axis Value Plunge Azimuth
T 1.10e+22 32 5
N 0.00e+00 7 271
P -1.10e+22 57 169
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.79e+21
Mxy 1.35e+21
Mxz 9.77e+21
Myy -4.19e+19
Myz -4.74e+20
Mzz -4.75e+21
##############
######################
############## ###########
############### T ############
################# ##############
####################################
######################################
-#######################################
-#######################################
-############-------------------##########
--#-------------------------------------##
##----------------------------------------
##----------------------------------------
##--------------------------------------
###----------------- -----------------
###---------------- P ----------------
###--------------- ---------------
####------------------------------
####--------------------------
#####---------------------##
#######-----------####
##############
Global CMT Convention Moment Tensor:
R T P
-4.75e+21 9.77e+21 4.74e+20
9.77e+21 4.79e+21 -1.35e+21
4.74e+20 -1.35e+21 -4.19e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190415142527/index.html
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STK = 120
DIP = 15
RAKE = -60
MW = 3.96
HS = 26.0
The NDK file is 20190415142527.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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 95 45 90 3.49 0.2725
WVFGRD96 2.0 270 45 90 3.63 0.3658
WVFGRD96 3.0 90 40 90 3.68 0.3359
WVFGRD96 4.0 90 35 85 3.68 0.2974
WVFGRD96 5.0 185 10 0 3.68 0.3314
WVFGRD96 6.0 180 10 -5 3.69 0.3979
WVFGRD96 7.0 180 10 -5 3.69 0.4511
WVFGRD96 8.0 170 10 -15 3.78 0.4885
WVFGRD96 9.0 165 10 -20 3.79 0.5380
WVFGRD96 10.0 165 10 -20 3.80 0.5796
WVFGRD96 11.0 165 15 -20 3.80 0.6145
WVFGRD96 12.0 155 15 -30 3.81 0.6452
WVFGRD96 13.0 120 10 -65 3.82 0.6701
WVFGRD96 14.0 125 15 -60 3.83 0.6929
WVFGRD96 15.0 120 15 -65 3.84 0.7134
WVFGRD96 16.0 115 15 -70 3.85 0.7310
WVFGRD96 17.0 115 15 -70 3.86 0.7460
WVFGRD96 18.0 115 15 -70 3.87 0.7585
WVFGRD96 19.0 115 15 -70 3.88 0.7688
WVFGRD96 20.0 115 15 -70 3.89 0.7770
WVFGRD96 21.0 120 15 -65 3.91 0.7841
WVFGRD96 22.0 115 15 -70 3.92 0.7902
WVFGRD96 23.0 110 15 -75 3.93 0.7944
WVFGRD96 24.0 120 15 -60 3.94 0.7978
WVFGRD96 25.0 120 15 -60 3.95 0.8002
WVFGRD96 26.0 120 15 -60 3.96 0.8012
WVFGRD96 27.0 120 15 -60 3.97 0.8003
WVFGRD96 28.0 115 10 -70 3.98 0.7995
WVFGRD96 29.0 125 10 -55 3.99 0.7971
WVFGRD96 30.0 130 10 -50 4.00 0.7934
WVFGRD96 31.0 130 10 -50 4.01 0.7883
WVFGRD96 32.0 130 10 -50 4.01 0.7813
WVFGRD96 33.0 135 10 -45 4.02 0.7729
WVFGRD96 34.0 135 10 -45 4.02 0.7632
WVFGRD96 35.0 140 10 -40 4.03 0.7521
WVFGRD96 36.0 140 10 -40 4.03 0.7402
WVFGRD96 37.0 145 10 -35 4.03 0.7285
WVFGRD96 38.0 145 10 -35 4.03 0.7158
WVFGRD96 39.0 155 10 -25 4.03 0.7022
WVFGRD96 40.0 140 5 -40 4.18 0.6880
WVFGRD96 41.0 155 5 -25 4.18 0.6776
WVFGRD96 42.0 160 5 -15 4.19 0.6661
WVFGRD96 43.0 170 5 -5 4.19 0.6549
WVFGRD96 44.0 175 5 0 4.20 0.6425
WVFGRD96 45.0 185 5 10 4.20 0.6301
WVFGRD96 46.0 185 10 10 4.20 0.6180
WVFGRD96 47.0 195 10 25 4.20 0.6064
WVFGRD96 48.0 200 10 30 4.21 0.5948
WVFGRD96 49.0 210 10 40 4.21 0.5831
WVFGRD96 50.0 215 25 60 4.21 0.5784
WVFGRD96 51.0 215 25 60 4.22 0.5755
WVFGRD96 52.0 215 25 60 4.22 0.5728
WVFGRD96 53.0 220 25 65 4.23 0.5705
WVFGRD96 54.0 220 25 70 4.24 0.5683
WVFGRD96 55.0 220 25 70 4.24 0.5657
WVFGRD96 56.0 220 30 70 4.24 0.5643
WVFGRD96 57.0 220 30 70 4.25 0.5631
WVFGRD96 58.0 220 30 75 4.26 0.5615
WVFGRD96 59.0 220 30 75 4.26 0.5600
WVFGRD96 30.0 130 10 -50 4.00 0.7934
WVFGRD96 31.0 130 10 -50 4.01 0.7883
WVFGRD96 32.0 130 10 -50 4.01 0.7813
WVFGRD96 33.0 135 10 -45 4.02 0.7729
WVFGRD96 34.0 135 10 -45 4.02 0.7632
WVFGRD96 35.0 140 10 -40 4.03 0.7521
WVFGRD96 36.0 140 10 -40 4.03 0.7402
WVFGRD96 37.0 145 10 -35 4.03 0.7285
WVFGRD96 38.0 145 10 -35 4.03 0.7158
WVFGRD96 39.0 155 10 -25 4.03 0.7022
WVFGRD96 40.0 140 5 -40 4.18 0.6880
WVFGRD96 41.0 155 5 -25 4.18 0.6776
WVFGRD96 42.0 160 5 -15 4.19 0.6661
WVFGRD96 43.0 170 5 -5 4.19 0.6549
WVFGRD96 44.0 175 5 0 4.20 0.6425
WVFGRD96 45.0 185 5 10 4.20 0.6301
WVFGRD96 46.0 185 10 10 4.20 0.6180
WVFGRD96 47.0 195 10 25 4.20 0.6064
WVFGRD96 48.0 200 10 30 4.21 0.5948
WVFGRD96 49.0 210 10 40 4.21 0.5831
WVFGRD96 50.0 215 25 60 4.21 0.5784
WVFGRD96 51.0 215 25 60 4.22 0.5755
WVFGRD96 52.0 215 25 60 4.22 0.5728
WVFGRD96 53.0 220 25 65 4.23 0.5705
WVFGRD96 54.0 220 25 70 4.24 0.5683
WVFGRD96 55.0 220 25 70 4.24 0.5657
WVFGRD96 56.0 220 30 70 4.24 0.5643
WVFGRD96 57.0 220 30 70 4.25 0.5631
WVFGRD96 58.0 220 30 75 4.26 0.5615
WVFGRD96 59.0 220 30 75 4.26 0.5600
WVFGRD96 30.0 130 10 -50 4.00 0.7934
WVFGRD96 31.0 130 10 -50 4.01 0.7883
WVFGRD96 32.0 130 10 -50 4.01 0.7813
WVFGRD96 33.0 135 10 -45 4.02 0.7729
WVFGRD96 34.0 135 10 -45 4.02 0.7632
WVFGRD96 35.0 140 10 -40 4.03 0.7521
WVFGRD96 36.0 140 10 -40 4.03 0.7402
WVFGRD96 37.0 145 10 -35 4.03 0.7285
WVFGRD96 38.0 145 10 -35 4.03 0.7158
WVFGRD96 39.0 155 10 -25 4.03 0.7022
WVFGRD96 40.0 140 5 -40 4.18 0.6880
WVFGRD96 41.0 155 5 -25 4.18 0.6776
WVFGRD96 42.0 160 5 -15 4.19 0.6661
WVFGRD96 43.0 170 5 -5 4.19 0.6549
WVFGRD96 44.0 175 5 0 4.20 0.6425
WVFGRD96 45.0 185 5 10 4.20 0.6301
WVFGRD96 46.0 185 10 10 4.20 0.6180
WVFGRD96 47.0 195 10 25 4.20 0.6064
WVFGRD96 48.0 200 10 30 4.21 0.5948
WVFGRD96 49.0 210 10 40 4.21 0.5831
WVFGRD96 50.0 215 25 60 4.21 0.5784
WVFGRD96 51.0 215 25 60 4.22 0.5755
WVFGRD96 52.0 215 25 60 4.22 0.5728
WVFGRD96 53.0 220 25 65 4.23 0.5705
WVFGRD96 54.0 220 25 70 4.24 0.5683
WVFGRD96 55.0 220 25 70 4.24 0.5657
WVFGRD96 56.0 220 30 70 4.24 0.5643
WVFGRD96 57.0 220 30 70 4.25 0.5631
WVFGRD96 58.0 220 30 75 4.26 0.5615
WVFGRD96 59.0 220 30 75 4.26 0.5600
The best solution is
WVFGRD96 26.0 120 15 -60 3.96 0.8012
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 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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