The ANSS event ID is ak0147pznycy and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0147pznycy/executive.
2014/06/17 09:03:49 62.756 -150.728 95.4 4.5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2014/06/17 09:03:49:0 62.76 -150.73 95.4 4.5 Alaska
Stations used:
AK.BPAW AK.CCB AK.DHY AK.GHO AK.HDA AK.KNK AK.MCAR AK.MCK
AK.PPLA AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.TRF AK.VRDI
AK.WRH AT.PMR IM.IL31 IU.COLA
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 5.96e+22 dyne-cm
Mw = 4.45
Z = 98 km
Plane Strike Dip Rake
NP1 341 64 134
NP2 95 50 35
Principal Axes:
Axis Value Plunge Azimuth
T 5.96e+22 50 301
N 0.00e+00 39 138
P -5.96e+22 8 41
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.69e+22
Mxy -3.97e+22
Mxz 8.64e+21
Myy -6.75e+21
Myz -3.07e+22
Mzz 3.36e+22
#-------------
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###############----------- P -
##################---------- ---
#####################---------------
#######################---------------
########## ###########----------------
########## T ############---------------
########### #############---------------
-###########################--------------
--##########################--------------
----#########################------------#
-----#######################----------##
-------#####################--------####
----------#################----#######
---------------------------#########
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Global CMT Convention Moment Tensor:
R T P
3.36e+22 8.64e+21 3.07e+22
8.64e+21 -2.69e+22 3.97e+22
3.07e+22 3.97e+22 -6.75e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140617090349/index.html
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STK = 95
DIP = 50
RAKE = 35
MW = 4.45
HS = 98.0
The NDK file is 20140617090349.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 a -30 a 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 115 50 -100 3.68 0.2358
WVFGRD96 4.0 135 50 -75 3.78 0.2249
WVFGRD96 6.0 0 65 15 3.78 0.2243
WVFGRD96 8.0 0 65 20 3.84 0.2435
WVFGRD96 10.0 0 65 20 3.87 0.2653
WVFGRD96 12.0 -5 65 20 3.89 0.2786
WVFGRD96 14.0 355 65 20 3.90 0.2837
WVFGRD96 16.0 345 70 25 3.91 0.2829
WVFGRD96 18.0 345 70 25 3.92 0.2800
WVFGRD96 20.0 345 70 25 3.94 0.2773
WVFGRD96 22.0 345 70 25 3.95 0.2671
WVFGRD96 24.0 340 70 30 3.96 0.2564
WVFGRD96 26.0 340 75 30 3.97 0.2460
WVFGRD96 28.0 275 70 45 3.97 0.2443
WVFGRD96 30.0 275 70 45 3.99 0.2466
WVFGRD96 32.0 275 70 45 4.00 0.2419
WVFGRD96 34.0 70 75 -5 4.09 0.2368
WVFGRD96 36.0 65 75 -5 4.12 0.2366
WVFGRD96 38.0 75 80 -10 4.15 0.2424
WVFGRD96 40.0 100 80 -35 4.23 0.2525
WVFGRD96 42.0 100 80 -35 4.24 0.2598
WVFGRD96 44.0 105 80 -30 4.28 0.2665
WVFGRD96 46.0 105 80 -30 4.30 0.2731
WVFGRD96 48.0 100 80 -30 4.31 0.2797
WVFGRD96 50.0 100 80 -30 4.32 0.2877
WVFGRD96 52.0 90 80 -35 4.32 0.2970
WVFGRD96 54.0 95 85 -35 4.34 0.3097
WVFGRD96 56.0 95 90 -35 4.34 0.3212
WVFGRD96 58.0 275 90 35 4.36 0.3335
WVFGRD96 60.0 275 85 40 4.35 0.3463
WVFGRD96 62.0 90 35 35 4.33 0.3662
WVFGRD96 64.0 90 35 35 4.35 0.3881
WVFGRD96 66.0 95 35 40 4.36 0.4086
WVFGRD96 68.0 90 40 35 4.38 0.4294
WVFGRD96 70.0 90 40 35 4.39 0.4484
WVFGRD96 72.0 90 40 35 4.39 0.4645
WVFGRD96 74.0 95 40 35 4.41 0.4790
WVFGRD96 76.0 95 40 40 4.40 0.4913
WVFGRD96 78.0 100 40 45 4.41 0.5016
WVFGRD96 80.0 90 45 30 4.43 0.5105
WVFGRD96 82.0 95 45 35 4.43 0.5192
WVFGRD96 84.0 95 45 35 4.43 0.5268
WVFGRD96 86.0 95 45 35 4.43 0.5326
WVFGRD96 88.0 95 45 35 4.44 0.5371
WVFGRD96 90.0 95 45 35 4.44 0.5397
WVFGRD96 92.0 95 50 35 4.44 0.5424
WVFGRD96 94.0 95 50 35 4.45 0.5451
WVFGRD96 96.0 95 50 35 4.45 0.5463
WVFGRD96 98.0 95 50 35 4.45 0.5471
WVFGRD96 100.0 95 50 35 4.45 0.5470
WVFGRD96 102.0 95 55 30 4.47 0.5463
WVFGRD96 104.0 95 55 30 4.47 0.5464
WVFGRD96 106.0 95 55 30 4.47 0.5455
WVFGRD96 108.0 95 55 30 4.47 0.5441
WVFGRD96 110.0 95 55 35 4.46 0.5428
WVFGRD96 112.0 95 55 35 4.46 0.5405
WVFGRD96 114.0 95 55 35 4.46 0.5376
WVFGRD96 116.0 95 60 35 4.47 0.5353
WVFGRD96 118.0 95 60 35 4.47 0.5329
The best solution is
WVFGRD96 98.0 95 50 35 4.45 0.5471
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 a -30 a 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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