The ANSS event ID is ak0188d4oyaj and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0188d4oyaj/executive.
2018/07/01 08:20:16 63.068 -150.797 117.3 5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2018/07/01 08:20:16:0 63.07 -150.80 117.3 5.0 Alaska
Stations used:
AK.BPAW AK.BWN AK.CAPN AK.CAST AK.CCB AK.CUT AK.DHY AK.DIV
AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.KLU AK.KNK
AK.KTH AK.MCK AK.MLY AK.NEA2 AK.PAX AK.PPLA AK.RC01 AK.RND
AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.WRH AT.PMR AT.SVW2
AV.SPU IM.IL31 IU.COLA TA.H21K TA.H24K TA.I20K TA.I23K
TA.J18K TA.J19K TA.J20K TA.J25K TA.L18K TA.L19K TA.M19K
TA.M22K TA.M24K TA.N19K TA.POKR
Filtering commands used:
cut o DIST/3.7 -50 o DIST/3.7 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.54e+23 dyne-cm
Mw = 4.87
Z = 126 km
Plane Strike Dip Rake
NP1 193 78 -112
NP2 75 25 -30
Principal Axes:
Axis Value Plunge Azimuth
T 2.54e+23 29 300
N 0.00e+00 21 197
P -2.54e+23 52 77
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.43e+22
Mxy -1.05e+23
Mxz 2.73e+22
Myy 5.30e+22
Myz -2.14e+23
Mzz -9.73e+22
###########---
##############--------
################------------
################--------------
#################-----------------
#### ###########------------------
##### T ##########--------------------
###### #########----------------------
##################---------- ---------
##################----------- P ---------#
##################----------- ---------#
##################----------------------##
#################-----------------------##
################----------------------##
-###############---------------------###
-#############--------------------####
--###########------------------#####
---#########----------------######
----######-------------#######
----------------############
------################
--############
Global CMT Convention Moment Tensor:
R T P
-9.73e+22 2.73e+22 2.14e+23
2.73e+22 4.43e+22 1.05e+23
2.14e+23 1.05e+23 5.30e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180701082016/index.html
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STK = 75
DIP = 25
RAKE = -30
MW = 4.87
HS = 126.0
The NDK file is 20180701082016.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/3.7 -50 o DIST/3.7 +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 0 85 5 3.81 0.1612
WVFGRD96 4.0 180 70 5 3.93 0.1852
WVFGRD96 6.0 180 70 10 4.00 0.2003
WVFGRD96 8.0 180 70 10 4.08 0.2149
WVFGRD96 10.0 175 75 -15 4.13 0.2221
WVFGRD96 12.0 175 75 -10 4.17 0.2238
WVFGRD96 14.0 0 80 10 4.20 0.2181
WVFGRD96 16.0 0 80 10 4.23 0.2110
WVFGRD96 18.0 270 85 15 4.25 0.2109
WVFGRD96 20.0 270 90 15 4.27 0.2153
WVFGRD96 22.0 270 70 10 4.30 0.2236
WVFGRD96 24.0 270 85 15 4.32 0.2334
WVFGRD96 26.0 90 85 -15 4.35 0.2466
WVFGRD96 28.0 90 85 -15 4.37 0.2600
WVFGRD96 30.0 90 80 -15 4.39 0.2723
WVFGRD96 32.0 90 85 -15 4.41 0.2834
WVFGRD96 34.0 90 80 -15 4.43 0.2935
WVFGRD96 36.0 90 80 -15 4.45 0.2997
WVFGRD96 38.0 90 80 -10 4.48 0.3026
WVFGRD96 40.0 90 80 -15 4.53 0.3038
WVFGRD96 42.0 90 75 -10 4.56 0.3021
WVFGRD96 44.0 85 70 -15 4.58 0.3031
WVFGRD96 46.0 85 70 -15 4.60 0.3059
WVFGRD96 48.0 85 70 -15 4.61 0.3091
WVFGRD96 50.0 85 70 -15 4.63 0.3141
WVFGRD96 52.0 85 65 -15 4.65 0.3202
WVFGRD96 54.0 95 60 15 4.68 0.3288
WVFGRD96 56.0 95 60 15 4.69 0.3363
WVFGRD96 58.0 95 60 10 4.70 0.3461
WVFGRD96 60.0 90 60 10 4.70 0.3540
WVFGRD96 62.0 90 60 5 4.70 0.3619
WVFGRD96 64.0 90 60 5 4.71 0.3691
WVFGRD96 66.0 90 60 5 4.72 0.3774
WVFGRD96 68.0 85 60 -10 4.72 0.3838
WVFGRD96 70.0 85 30 -15 4.76 0.3965
WVFGRD96 72.0 85 30 -15 4.77 0.4111
WVFGRD96 74.0 85 30 -15 4.77 0.4246
WVFGRD96 76.0 85 30 -15 4.78 0.4371
WVFGRD96 78.0 85 30 -15 4.79 0.4515
WVFGRD96 80.0 80 30 -20 4.79 0.4637
WVFGRD96 82.0 75 20 -25 4.81 0.4766
WVFGRD96 84.0 80 20 -20 4.81 0.4910
WVFGRD96 86.0 75 20 -25 4.82 0.5054
WVFGRD96 88.0 75 20 -25 4.82 0.5174
WVFGRD96 90.0 75 20 -25 4.83 0.5282
WVFGRD96 92.0 75 20 -25 4.83 0.5369
WVFGRD96 94.0 80 20 -25 4.84 0.5459
WVFGRD96 96.0 80 20 -25 4.84 0.5542
WVFGRD96 98.0 80 20 -25 4.85 0.5608
WVFGRD96 100.0 75 20 -30 4.85 0.5666
WVFGRD96 102.0 75 20 -30 4.85 0.5719
WVFGRD96 104.0 75 20 -30 4.85 0.5768
WVFGRD96 106.0 75 20 -30 4.86 0.5795
WVFGRD96 108.0 75 20 -30 4.86 0.5827
WVFGRD96 110.0 75 20 -30 4.86 0.5854
WVFGRD96 112.0 75 25 -30 4.86 0.5884
WVFGRD96 114.0 75 25 -30 4.86 0.5916
WVFGRD96 116.0 75 25 -30 4.86 0.5955
WVFGRD96 118.0 75 25 -30 4.86 0.5965
WVFGRD96 120.0 75 25 -30 4.86 0.5998
WVFGRD96 122.0 75 25 -30 4.87 0.6001
WVFGRD96 124.0 75 25 -30 4.87 0.6011
WVFGRD96 126.0 75 25 -30 4.87 0.6024
WVFGRD96 128.0 75 25 -30 4.87 0.6003
WVFGRD96 130.0 75 25 -30 4.87 0.6010
WVFGRD96 132.0 75 25 -30 4.87 0.5988
WVFGRD96 134.0 75 25 -30 4.87 0.5994
WVFGRD96 136.0 75 25 -30 4.87 0.5968
WVFGRD96 138.0 75 25 -30 4.87 0.5961
WVFGRD96 140.0 75 25 -30 4.88 0.5941
WVFGRD96 142.0 75 25 -35 4.88 0.5912
WVFGRD96 144.0 75 25 -35 4.88 0.5903
WVFGRD96 146.0 75 25 -35 4.88 0.5867
WVFGRD96 148.0 85 25 -25 4.89 0.5847
The best solution is
WVFGRD96 126.0 75 25 -30 4.87 0.6024
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/3.7 -50 o DIST/3.7 +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