The ANSS event ID is ak0188rwahak and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0188rwahak/executive.
2018/07/10 01:08:21 62.979 -150.636 113.4 5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2018/07/10 01:08:21:0 62.98 -150.64 113.4 5.0 Alaska
Stations used:
AK.BPAW AK.BWN AK.CCB AK.CUT AK.DHY AK.DIV AK.FID AK.FIRE
AK.GHO AK.GLI AK.HDA AK.KLU AK.KNK AK.MCK AK.MDM AK.MLY
AK.NEA2 AK.PAX AK.PPD AK.RC01 AK.RND AK.SAW AK.SCM AK.SKN
AK.SSN AK.SWD AK.WRH AT.PMR AV.SPU IM.IL31 IU.COLA TA.G23K
TA.H19K TA.H21K TA.H23K TA.H24K TA.I20K TA.J20K TA.J25K
TA.J26L TA.K20K TA.L18K TA.L19K TA.M20K TA.M22K TA.M24K
TA.N19K TA.N25K TA.O22K TA.POKR
Filtering commands used:
cut o DIST/3.5 -40 o DIST/3.5 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.82e+23 dyne-cm
Mw = 4.90
Z = 112 km
Plane Strike Dip Rake
NP1 27 75 103
NP2 165 20 50
Principal Axes:
Axis Value Plunge Azimuth
T 2.82e+23 58 315
N 0.00e+00 13 203
P -2.82e+23 29 106
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.17e+22
Mxy 1.90e+22
Mxz 1.22e+23
Myy -1.60e+23
Myz -2.04e+23
Mzz 1.39e+23
##############
--##################--
---####################-----
--######################------
---#######################--------
---#######################----------
---######## #############-----------
----######## T ############-------------
---######### ###########--------------
----#######################---------------
----######################----------------
----#####################-----------------
----####################---------- -----
----##################----------- P ----
----#################------------ ----
----###############-------------------
----############--------------------
-----#########--------------------
----#######-------------------
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---##-----------------
######--------
Global CMT Convention Moment Tensor:
R T P
1.39e+23 1.22e+23 2.04e+23
1.22e+23 2.17e+22 -1.90e+22
2.04e+23 -1.90e+22 -1.60e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180710010821/index.html
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STK = 165
DIP = 20
RAKE = 50
MW = 4.90
HS = 112.0
The NDK file is 20180710010821.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/3.5 -40 o DIST/3.5 +70 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 55 45 -90 3.95 0.1073
WVFGRD96 4.0 200 70 35 3.97 0.1070
WVFGRD96 6.0 5 75 -40 4.02 0.1190
WVFGRD96 8.0 5 70 -40 4.11 0.1303
WVFGRD96 10.0 15 60 25 4.14 0.1397
WVFGRD96 12.0 200 65 40 4.18 0.1477
WVFGRD96 14.0 200 65 40 4.21 0.1523
WVFGRD96 16.0 200 65 40 4.24 0.1529
WVFGRD96 18.0 195 65 40 4.26 0.1507
WVFGRD96 20.0 195 65 40 4.29 0.1468
WVFGRD96 22.0 195 65 40 4.31 0.1432
WVFGRD96 24.0 195 65 40 4.33 0.1397
WVFGRD96 26.0 285 45 10 4.36 0.1401
WVFGRD96 28.0 285 45 10 4.38 0.1427
WVFGRD96 30.0 285 50 10 4.40 0.1455
WVFGRD96 32.0 285 50 10 4.43 0.1529
WVFGRD96 34.0 285 55 15 4.45 0.1594
WVFGRD96 36.0 275 75 -20 4.47 0.1689
WVFGRD96 38.0 280 80 -15 4.51 0.1755
WVFGRD96 40.0 90 50 -30 4.60 0.1912
WVFGRD96 42.0 85 45 -35 4.63 0.1910
WVFGRD96 44.0 90 50 -30 4.65 0.1922
WVFGRD96 46.0 90 45 -30 4.67 0.1937
WVFGRD96 48.0 95 45 -25 4.69 0.1965
WVFGRD96 50.0 125 40 25 4.71 0.2017
WVFGRD96 52.0 125 40 25 4.73 0.2186
WVFGRD96 54.0 125 40 20 4.75 0.2348
WVFGRD96 56.0 125 40 20 4.76 0.2492
WVFGRD96 58.0 120 35 20 4.77 0.2621
WVFGRD96 60.0 120 35 20 4.78 0.2762
WVFGRD96 62.0 140 30 30 4.79 0.2899
WVFGRD96 64.0 145 30 30 4.80 0.3045
WVFGRD96 66.0 135 25 25 4.82 0.3201
WVFGRD96 68.0 135 25 25 4.83 0.3343
WVFGRD96 70.0 140 20 30 4.84 0.3498
WVFGRD96 72.0 145 20 30 4.84 0.3632
WVFGRD96 74.0 145 20 30 4.85 0.3782
WVFGRD96 76.0 145 20 30 4.86 0.3913
WVFGRD96 78.0 150 20 35 4.86 0.4025
WVFGRD96 80.0 150 20 35 4.87 0.4139
WVFGRD96 82.0 150 20 35 4.87 0.4240
WVFGRD96 84.0 150 20 35 4.87 0.4324
WVFGRD96 86.0 155 20 40 4.87 0.4398
WVFGRD96 88.0 155 20 40 4.88 0.4461
WVFGRD96 90.0 155 20 40 4.88 0.4518
WVFGRD96 92.0 155 20 40 4.88 0.4563
WVFGRD96 94.0 155 20 40 4.89 0.4597
WVFGRD96 96.0 155 20 40 4.89 0.4622
WVFGRD96 98.0 155 20 40 4.89 0.4643
WVFGRD96 100.0 160 20 45 4.89 0.4658
WVFGRD96 102.0 160 20 45 4.89 0.4665
WVFGRD96 104.0 160 20 45 4.89 0.4709
WVFGRD96 106.0 160 20 45 4.89 0.4774
WVFGRD96 108.0 165 20 50 4.89 0.4824
WVFGRD96 110.0 165 20 50 4.89 0.4855
WVFGRD96 112.0 165 20 50 4.90 0.4863
WVFGRD96 114.0 165 20 50 4.90 0.4858
WVFGRD96 116.0 165 20 50 4.90 0.4848
WVFGRD96 118.0 165 20 50 4.90 0.4844
WVFGRD96 120.0 165 20 50 4.90 0.4831
WVFGRD96 122.0 165 20 50 4.90 0.4821
WVFGRD96 124.0 165 20 50 4.90 0.4808
WVFGRD96 126.0 160 25 45 4.90 0.4791
WVFGRD96 128.0 160 25 45 4.90 0.4768
WVFGRD96 130.0 160 25 45 4.90 0.4748
WVFGRD96 132.0 160 25 45 4.90 0.4724
WVFGRD96 134.0 160 25 45 4.90 0.4697
WVFGRD96 136.0 160 25 45 4.91 0.4675
WVFGRD96 138.0 160 25 45 4.91 0.4644
WVFGRD96 140.0 160 25 45 4.91 0.4624
WVFGRD96 142.0 160 25 45 4.91 0.4595
WVFGRD96 144.0 160 25 45 4.91 0.4559
WVFGRD96 146.0 160 25 45 4.91 0.4523
WVFGRD96 148.0 160 25 45 4.91 0.4494
The best solution is
WVFGRD96 112.0 165 20 50 4.90 0.4863
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/3.5 -40 o DIST/3.5 +70 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