The ANSS event ID is ak0177q3cz5d and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0177q3cz5d/executive.
2017/06/17 15:24:10 62.465 -149.089 39.4 3.7 Alaska
USGS/SLU Moment Tensor Solution
ENS 2017/06/17 15:24:10:0 62.47 -149.09 39.4 3.7 Alaska
Stations used:
AK.BWN AK.CUT AK.DHY AK.GLI AK.KLU AK.KNK AK.MCK AK.RC01
AK.RND AK.SAW AK.SCM AT.PMR TA.K20K TA.M22K TA.M24K
Filtering commands used:
cut o DIST/3.5 -30 o DIST/3.5 +50
rtr
taper w 0.1
hp c 0.04 n 3
lp c 0.12 n 3
Best Fitting Double Couple
Mo = 4.79e+21 dyne-cm
Mw = 3.72
Z = 60 km
Plane Strike Dip Rake
NP1 305 75 -40
NP2 47 52 -161
Principal Axes:
Axis Value Plunge Azimuth
T 4.79e+21 15 1
N 0.00e+00 48 108
P -4.79e+21 38 259
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.36e+21
Mxy -4.89e+20
Mxz 1.64e+21
Myy -2.82e+21
Myz 2.31e+21
Mzz -1.54e+21
###### #####
########## T #########
############# ############
##############################
################################--
-------##########################---
-------------#####################----
-----------------##################-----
--------------------##############------
------------------------###########-------
--------------------------########--------
------- ------------------#####---------
------- P --------------------------------
------ --------------------##---------
---------------------------######-------
------------------------##########----
---------------------#############--
----------------##################
----------####################
############################
######################
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Global CMT Convention Moment Tensor:
R T P
-1.54e+21 1.64e+21 -2.31e+21
1.64e+21 4.36e+21 4.89e+20
-2.31e+21 4.89e+20 -2.82e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170617152410/index.html
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STK = 305
DIP = 75
RAKE = -40
MW = 3.72
HS = 60.0
The NDK file is 20170617152410.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 -30 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.12 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 220 80 -5 2.64 0.1362
WVFGRD96 2.0 220 90 -5 2.79 0.1785
WVFGRD96 3.0 50 80 40 2.91 0.1961
WVFGRD96 4.0 50 80 40 2.96 0.2134
WVFGRD96 5.0 30 40 -30 3.04 0.2340
WVFGRD96 6.0 30 40 -30 3.07 0.2515
WVFGRD96 7.0 35 45 -25 3.10 0.2628
WVFGRD96 8.0 30 40 -30 3.17 0.2685
WVFGRD96 9.0 35 40 -25 3.20 0.2715
WVFGRD96 10.0 35 40 -25 3.22 0.2719
WVFGRD96 11.0 35 45 -20 3.24 0.2697
WVFGRD96 12.0 35 45 -20 3.26 0.2662
WVFGRD96 13.0 45 50 10 3.26 0.2620
WVFGRD96 14.0 45 50 10 3.28 0.2586
WVFGRD96 15.0 45 50 10 3.30 0.2539
WVFGRD96 16.0 45 50 10 3.31 0.2482
WVFGRD96 17.0 45 50 10 3.33 0.2405
WVFGRD96 18.0 125 75 -35 3.32 0.2426
WVFGRD96 19.0 125 75 -35 3.34 0.2501
WVFGRD96 20.0 130 80 -35 3.36 0.2596
WVFGRD96 21.0 130 80 -30 3.37 0.2703
WVFGRD96 22.0 315 75 40 3.41 0.2854
WVFGRD96 23.0 315 75 40 3.43 0.3000
WVFGRD96 24.0 315 75 40 3.45 0.3138
WVFGRD96 25.0 315 75 40 3.46 0.3265
WVFGRD96 26.0 315 75 35 3.46 0.3370
WVFGRD96 27.0 320 75 40 3.48 0.3477
WVFGRD96 28.0 315 80 35 3.47 0.3564
WVFGRD96 29.0 315 55 10 3.48 0.3657
WVFGRD96 30.0 315 55 10 3.49 0.3767
WVFGRD96 31.0 310 60 -5 3.48 0.3854
WVFGRD96 32.0 310 55 -5 3.49 0.3949
WVFGRD96 33.0 310 55 -5 3.50 0.4030
WVFGRD96 34.0 310 55 -10 3.51 0.4098
WVFGRD96 35.0 310 55 -10 3.51 0.4138
WVFGRD96 36.0 310 55 -10 3.52 0.4169
WVFGRD96 37.0 310 60 -15 3.52 0.4192
WVFGRD96 38.0 310 60 -15 3.54 0.4234
WVFGRD96 39.0 310 60 -15 3.55 0.4285
WVFGRD96 40.0 305 55 -25 3.61 0.4264
WVFGRD96 41.0 305 50 -20 3.63 0.4294
WVFGRD96 42.0 305 55 -25 3.64 0.4312
WVFGRD96 43.0 305 55 -25 3.65 0.4311
WVFGRD96 44.0 305 55 -25 3.66 0.4305
WVFGRD96 45.0 305 65 -35 3.67 0.4310
WVFGRD96 46.0 305 65 -35 3.67 0.4334
WVFGRD96 47.0 305 65 -35 3.68 0.4353
WVFGRD96 48.0 305 65 -35 3.69 0.4376
WVFGRD96 49.0 305 65 -35 3.69 0.4413
WVFGRD96 50.0 305 65 -35 3.70 0.4443
WVFGRD96 51.0 305 70 -40 3.70 0.4465
WVFGRD96 52.0 305 70 -40 3.71 0.4482
WVFGRD96 53.0 305 70 -40 3.71 0.4505
WVFGRD96 54.0 305 70 -40 3.71 0.4531
WVFGRD96 55.0 305 70 -40 3.71 0.4549
WVFGRD96 56.0 305 70 -40 3.72 0.4546
WVFGRD96 57.0 305 70 -40 3.72 0.4564
WVFGRD96 58.0 305 70 -40 3.72 0.4555
WVFGRD96 59.0 305 75 -40 3.72 0.4555
WVFGRD96 60.0 305 75 -40 3.72 0.4576
WVFGRD96 61.0 305 75 -40 3.72 0.4571
WVFGRD96 62.0 305 75 -40 3.72 0.4554
WVFGRD96 63.0 305 75 -40 3.72 0.4566
WVFGRD96 64.0 305 75 -40 3.72 0.4555
WVFGRD96 65.0 305 75 -40 3.72 0.4563
WVFGRD96 66.0 305 75 -40 3.72 0.4557
WVFGRD96 67.0 305 75 -40 3.72 0.4525
WVFGRD96 68.0 305 75 -40 3.73 0.4553
WVFGRD96 69.0 305 75 -40 3.73 0.4522
WVFGRD96 70.0 305 75 -40 3.73 0.4525
WVFGRD96 71.0 305 75 -40 3.73 0.4514
WVFGRD96 72.0 305 80 -45 3.74 0.4513
WVFGRD96 73.0 305 80 -40 3.73 0.4493
WVFGRD96 74.0 305 80 -45 3.74 0.4488
WVFGRD96 75.0 305 80 -40 3.73 0.4484
WVFGRD96 76.0 305 80 -40 3.73 0.4457
WVFGRD96 77.0 305 80 -40 3.73 0.4462
WVFGRD96 78.0 295 70 -55 3.75 0.4446
WVFGRD96 79.0 305 80 -40 3.73 0.4420
WVFGRD96 80.0 295 70 -55 3.75 0.4428
WVFGRD96 81.0 295 70 -55 3.75 0.4393
WVFGRD96 82.0 295 70 -55 3.75 0.4403
WVFGRD96 83.0 295 70 -55 3.75 0.4365
WVFGRD96 84.0 300 75 -50 3.75 0.4362
WVFGRD96 85.0 300 75 -50 3.75 0.4353
WVFGRD96 86.0 300 75 -50 3.75 0.4339
WVFGRD96 87.0 300 75 -50 3.75 0.4337
WVFGRD96 88.0 295 70 -55 3.75 0.4318
WVFGRD96 89.0 295 70 -55 3.76 0.4317
WVFGRD96 90.0 295 70 -55 3.76 0.4288
WVFGRD96 91.0 295 70 -55 3.76 0.4297
WVFGRD96 92.0 295 70 -55 3.76 0.4276
WVFGRD96 93.0 295 70 -55 3.76 0.4272
WVFGRD96 94.0 295 70 -55 3.76 0.4268
WVFGRD96 95.0 295 70 -55 3.76 0.4244
WVFGRD96 96.0 295 70 -55 3.76 0.4255
WVFGRD96 97.0 295 70 -55 3.76 0.4227
WVFGRD96 98.0 295 70 -55 3.76 0.4235
WVFGRD96 99.0 295 70 -55 3.76 0.4214
The best solution is
WVFGRD96 60.0 305 75 -40 3.72 0.4576
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 -30 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.12 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