The ANSS event ID is ak0168vinufu and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0168vinufu/executive.
2016/07/11 20:05:57 63.806 -149.228 123.0 4.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2016/07/11 20:05:57:0 63.81 -149.23 123.0 4.1 Alaska
Stations used:
AK.BPAW AK.BWN AK.CAST AK.CCB AK.CUT AK.DHY AK.GHO AK.GLI
AK.HDA AK.KNK AK.KTH AK.MCK AK.MDM AK.NEA2 AK.PAX AK.RC01
AK.RND AK.SAW AK.SCM AK.SCRK AK.TRF AK.WRH AT.PMR IM.IL31
IU.COLA TA.H23K TA.H24K TA.I23K TA.J20K TA.J25K TA.J26L
TA.K20K TA.L19K TA.L26K TA.M22K TA.M26K TA.POKR
Filtering commands used:
cut o DIST/4.5 -30 o DIST/4.5 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.04e+22 dyne-cm
Mw = 4.14
Z = 140 km
Plane Strike Dip Rake
NP1 339 66 129
NP2 95 45 35
Principal Axes:
Axis Value Plunge Azimuth
T 2.04e+22 52 295
N 0.00e+00 35 140
P -2.04e+22 12 41
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.57e+21
Mxy -1.27e+22
Mxz 1.03e+21
Myy -2.14e+21
Myz -1.18e+22
Mzz 1.17e+22
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##############------------ P -
#################----------- ---
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########## ###########----------------
########## T ############---------------
########### ############----------------
-##########################---------------
--##########################--------------
---#########################-------------#
----########################-----------#
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Global CMT Convention Moment Tensor:
R T P
1.17e+22 1.03e+21 1.18e+22
1.03e+21 -9.57e+21 1.27e+22
1.18e+22 1.27e+22 -2.14e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160711200557/index.html
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STK = 95
DIP = 45
RAKE = 35
MW = 4.14
HS = 140.0
The NDK file is 20160711200557.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/4.5 -30 o DIST/4.5 +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 2.0 145 50 -80 3.26 0.2355
WVFGRD96 4.0 205 20 -20 3.25 0.1769
WVFGRD96 6.0 130 90 65 3.27 0.2349
WVFGRD96 8.0 215 25 -10 3.37 0.2668
WVFGRD96 10.0 140 75 60 3.41 0.2977
WVFGRD96 12.0 145 70 65 3.45 0.3168
WVFGRD96 14.0 240 40 35 3.49 0.3221
WVFGRD96 16.0 245 40 35 3.52 0.3249
WVFGRD96 18.0 240 45 35 3.56 0.3210
WVFGRD96 20.0 240 45 30 3.58 0.3120
WVFGRD96 22.0 240 45 25 3.61 0.2987
WVFGRD96 24.0 240 45 25 3.62 0.2853
WVFGRD96 26.0 290 65 45 3.63 0.2737
WVFGRD96 28.0 290 65 45 3.65 0.2646
WVFGRD96 30.0 285 65 40 3.67 0.2544
WVFGRD96 32.0 285 65 40 3.67 0.2404
WVFGRD96 34.0 175 55 -40 3.69 0.2527
WVFGRD96 36.0 175 55 -40 3.70 0.2662
WVFGRD96 38.0 175 50 -45 3.71 0.2763
WVFGRD96 40.0 165 50 -55 3.82 0.3048
WVFGRD96 42.0 150 40 -90 3.84 0.3093
WVFGRD96 44.0 150 40 -90 3.86 0.3084
WVFGRD96 46.0 335 50 -85 3.88 0.3042
WVFGRD96 48.0 335 50 -85 3.89 0.2991
WVFGRD96 50.0 335 50 -85 3.90 0.2932
WVFGRD96 52.0 340 50 -80 3.91 0.2872
WVFGRD96 54.0 340 50 -80 3.91 0.2807
WVFGRD96 56.0 335 50 -75 3.91 0.2747
WVFGRD96 58.0 340 50 -70 3.92 0.2697
WVFGRD96 60.0 250 55 25 3.98 0.2807
WVFGRD96 62.0 275 60 40 3.96 0.3031
WVFGRD96 64.0 275 60 40 3.98 0.3384
WVFGRD96 66.0 275 60 40 3.99 0.3720
WVFGRD96 68.0 275 60 40 4.01 0.4007
WVFGRD96 70.0 100 45 65 3.99 0.4277
WVFGRD96 72.0 100 45 65 4.00 0.4555
WVFGRD96 74.0 100 45 60 4.01 0.4780
WVFGRD96 76.0 100 45 60 4.01 0.4980
WVFGRD96 78.0 100 45 55 4.02 0.5172
WVFGRD96 80.0 100 45 55 4.03 0.5358
WVFGRD96 82.0 100 45 55 4.03 0.5517
WVFGRD96 84.0 100 45 55 4.03 0.5656
WVFGRD96 86.0 100 45 50 4.04 0.5793
WVFGRD96 88.0 100 45 50 4.05 0.5923
WVFGRD96 90.0 100 45 50 4.05 0.6039
WVFGRD96 92.0 100 45 50 4.05 0.6144
WVFGRD96 94.0 95 45 45 4.06 0.6256
WVFGRD96 96.0 95 45 45 4.06 0.6355
WVFGRD96 98.0 95 45 45 4.06 0.6452
WVFGRD96 100.0 95 45 45 4.07 0.6552
WVFGRD96 102.0 95 45 45 4.07 0.6635
WVFGRD96 104.0 95 45 45 4.07 0.6713
WVFGRD96 106.0 95 45 40 4.08 0.6786
WVFGRD96 108.0 95 45 40 4.09 0.6843
WVFGRD96 110.0 95 45 40 4.09 0.6924
WVFGRD96 112.0 95 45 40 4.09 0.6979
WVFGRD96 114.0 95 45 40 4.10 0.7028
WVFGRD96 116.0 95 45 40 4.10 0.7076
WVFGRD96 118.0 95 45 40 4.10 0.7117
WVFGRD96 120.0 95 45 40 4.11 0.7159
WVFGRD96 122.0 95 45 40 4.11 0.7189
WVFGRD96 124.0 95 45 40 4.11 0.7224
WVFGRD96 126.0 95 45 40 4.11 0.7244
WVFGRD96 128.0 95 45 40 4.12 0.7270
WVFGRD96 130.0 95 45 40 4.12 0.7281
WVFGRD96 132.0 95 45 40 4.12 0.7293
WVFGRD96 134.0 95 45 40 4.12 0.7313
WVFGRD96 136.0 95 45 40 4.13 0.7317
WVFGRD96 138.0 95 45 40 4.13 0.7326
WVFGRD96 140.0 95 45 35 4.14 0.7335
WVFGRD96 142.0 95 45 40 4.13 0.7323
WVFGRD96 144.0 95 45 35 4.14 0.7332
WVFGRD96 146.0 95 45 35 4.15 0.7315
WVFGRD96 148.0 95 45 40 4.14 0.7315
The best solution is
WVFGRD96 140.0 95 45 35 4.14 0.7335
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/4.5 -30 o DIST/4.5 +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