The ANSS event ID is ak0169vkoz7q and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0169vkoz7q/executive.
2016/08/02 00:25:01 62.049 -149.391 38.2 4.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2016/08/02 00:25:01:0 62.05 -149.39 38.2 4.1 Alaska
Stations used:
AK.CUT AK.DHY AK.GHO AK.GLI AK.HDA AK.HIN AK.KNK AK.PWL
AK.RC01 AK.SAW AK.SCM AK.WRH AT.PMR TA.J20K TA.M22K TA.N25K
TA.O22K
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +30
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.72e+22 dyne-cm
Mw = 4.09
Z = 52 km
Plane Strike Dip Rake
NP1 336 52 -117
NP2 195 45 -60
Principal Axes:
Axis Value Plunge Azimuth
T 1.72e+22 4 84
N 0.00e+00 21 353
P -1.72e+22 69 184
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.04e+21
Mxy 1.54e+21
Mxz 5.87e+21
Myy 1.69e+22
Myz 1.57e+21
Mzz -1.49e+22
----------####
#######---############
###########--###############
##########-------#############
##########----------##############
##########-------------#############
##########---------------#############
##########-----------------#############
##########------------------##########
##########--------------------######### T
##########---------------------########
#########----------------------###########
#########-----------------------##########
########---------- ----------#########
########---------- P ----------#########
########--------- ----------########
#######----------------------#######
######----------------------######
#####---------------------####
#####-------------------####
###-----------------##
#-------------
Global CMT Convention Moment Tensor:
R T P
-1.49e+22 5.87e+21 -1.57e+21
5.87e+21 -2.04e+21 -1.54e+21
-1.57e+21 -1.54e+21 1.69e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160802002501/index.html
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STK = 195
DIP = 45
RAKE = -60
MW = 4.09
HS = 52.0
The NDK file is 20160802002501.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 +30 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 1.0 185 40 90 3.18 0.2201
WVFGRD96 2.0 -5 50 85 3.33 0.2746
WVFGRD96 3.0 320 20 50 3.38 0.2450
WVFGRD96 4.0 320 20 45 3.38 0.2873
WVFGRD96 5.0 320 25 45 3.38 0.3098
WVFGRD96 6.0 320 25 45 3.39 0.3265
WVFGRD96 7.0 325 25 55 3.41 0.3390
WVFGRD96 8.0 330 20 60 3.49 0.3452
WVFGRD96 9.0 335 20 65 3.50 0.3527
WVFGRD96 10.0 335 20 70 3.53 0.3618
WVFGRD96 11.0 335 20 70 3.54 0.3677
WVFGRD96 12.0 330 25 65 3.55 0.3697
WVFGRD96 13.0 330 25 65 3.57 0.3703
WVFGRD96 14.0 330 25 65 3.58 0.3677
WVFGRD96 15.0 345 25 80 3.59 0.3636
WVFGRD96 16.0 340 25 75 3.60 0.3580
WVFGRD96 17.0 340 25 75 3.61 0.3509
WVFGRD96 18.0 330 25 65 3.62 0.3423
WVFGRD96 19.0 330 25 65 3.63 0.3336
WVFGRD96 20.0 25 45 -40 3.64 0.3280
WVFGRD96 21.0 25 45 -45 3.66 0.3303
WVFGRD96 22.0 25 40 -45 3.67 0.3310
WVFGRD96 23.0 25 40 -45 3.68 0.3319
WVFGRD96 24.0 25 40 -45 3.69 0.3312
WVFGRD96 25.0 25 40 -45 3.70 0.3277
WVFGRD96 26.0 20 40 -55 3.70 0.3227
WVFGRD96 27.0 240 40 -25 3.74 0.3204
WVFGRD96 28.0 245 35 -20 3.76 0.3358
WVFGRD96 29.0 240 35 -30 3.77 0.3523
WVFGRD96 30.0 240 35 -30 3.78 0.3670
WVFGRD96 31.0 240 35 -30 3.79 0.3832
WVFGRD96 32.0 175 40 -85 3.80 0.4087
WVFGRD96 33.0 175 40 -85 3.81 0.4448
WVFGRD96 34.0 175 40 -85 3.83 0.4758
WVFGRD96 35.0 180 40 -80 3.84 0.5060
WVFGRD96 36.0 180 40 -80 3.85 0.5370
WVFGRD96 37.0 180 40 -80 3.86 0.5623
WVFGRD96 38.0 180 40 -75 3.89 0.5842
WVFGRD96 39.0 180 40 -75 3.90 0.6013
WVFGRD96 40.0 185 40 -75 3.98 0.6134
WVFGRD96 41.0 185 40 -75 3.99 0.6141
WVFGRD96 42.0 185 40 -70 4.01 0.6193
WVFGRD96 43.0 185 40 -70 4.02 0.6232
WVFGRD96 44.0 185 40 -70 4.03 0.6269
WVFGRD96 45.0 185 40 -70 4.04 0.6320
WVFGRD96 46.0 185 40 -70 4.05 0.6347
WVFGRD96 47.0 185 40 -70 4.05 0.6380
WVFGRD96 48.0 190 40 -65 4.06 0.6387
WVFGRD96 49.0 190 40 -65 4.07 0.6405
WVFGRD96 50.0 185 40 -65 4.08 0.6400
WVFGRD96 51.0 195 45 -60 4.08 0.6401
WVFGRD96 52.0 195 45 -60 4.09 0.6408
WVFGRD96 53.0 195 45 -60 4.09 0.6387
WVFGRD96 54.0 195 45 -60 4.09 0.6387
WVFGRD96 55.0 195 45 -55 4.10 0.6337
WVFGRD96 56.0 195 45 -55 4.11 0.6332
WVFGRD96 57.0 195 45 -55 4.11 0.6293
WVFGRD96 58.0 195 45 -55 4.11 0.6252
WVFGRD96 59.0 195 45 -55 4.11 0.6220
WVFGRD96 60.0 195 45 -55 4.11 0.6150
WVFGRD96 61.0 200 50 -50 4.12 0.6133
WVFGRD96 62.0 200 50 -50 4.12 0.6081
WVFGRD96 63.0 200 50 -50 4.12 0.6049
WVFGRD96 64.0 200 50 -50 4.12 0.6015
WVFGRD96 65.0 200 50 -50 4.12 0.5958
WVFGRD96 66.0 200 50 -50 4.12 0.5912
WVFGRD96 67.0 205 50 -45 4.13 0.5877
WVFGRD96 68.0 205 50 -45 4.13 0.5820
WVFGRD96 69.0 205 50 -45 4.13 0.5780
WVFGRD96 70.0 205 50 -45 4.13 0.5723
WVFGRD96 71.0 205 50 -45 4.13 0.5683
WVFGRD96 72.0 205 55 -45 4.14 0.5625
WVFGRD96 73.0 205 55 -45 4.14 0.5588
WVFGRD96 74.0 210 55 -40 4.15 0.5555
WVFGRD96 75.0 210 55 -40 4.15 0.5511
WVFGRD96 76.0 210 55 -40 4.15 0.5468
WVFGRD96 77.0 210 55 -40 4.15 0.5436
WVFGRD96 78.0 210 55 -40 4.15 0.5395
WVFGRD96 79.0 210 55 -40 4.15 0.5346
The best solution is
WVFGRD96 52.0 195 45 -60 4.09 0.6408
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 +30 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