The ANSS event ID is ak0145dpas9d and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0145dpas9d/executive.
2014/04/27 12:46:55 63.815 -149.172 111.7 3.9 Alaska
USGS/SLU Moment Tensor Solution
ENS 2014/04/27 12:46:55:0 63.81 -149.17 111.7 3.9 Alaska
Stations used:
AK.BPAW AK.CCB AK.HDA AK.KTH AK.MCK AK.NEA AK.PPD AK.RND
AK.SAW AK.SCM AK.TRF AK.WRH AT.PMR IM.IL31 IU.COLA
Filtering commands used:
cut a -30 a 80
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.10e+22 dyne-cm
Mw = 3.96
Z = 126 km
Plane Strike Dip Rake
NP1 306 54 110
NP2 95 40 65
Principal Axes:
Axis Value Plunge Azimuth
T 1.10e+22 72 268
N 0.00e+00 16 115
P -1.10e+22 7 23
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.19e+21
Mxy -3.78e+21
Mxz -1.41e+21
Myy -5.92e+20
Myz -3.69e+21
Mzz 9.79e+21
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----------------- P --
-------------------- -----
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#############---------------------
###################-----------------
#######################---------------
##########################--------------
############################------------
###############################-----------
-############## ###############---------
-############## T ################--------
---############ #################------#
---################################----#
-----###############################-###
------############################-###
---------#####################-----#
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Global CMT Convention Moment Tensor:
R T P
9.79e+21 -1.41e+21 3.69e+21
-1.41e+21 -9.19e+21 3.78e+21
3.69e+21 3.78e+21 -5.92e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140427124655/index.html
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STK = 95
DIP = 40
RAKE = 65
MW = 3.96
HS = 126.0
The NDK file is 20140427124655.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 80 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 2.0 140 45 -85 3.25 0.4127
WVFGRD96 4.0 340 40 -55 3.32 0.3227
WVFGRD96 6.0 360 35 -20 3.30 0.3073
WVFGRD96 8.0 25 30 -30 3.35 0.3374
WVFGRD96 10.0 35 35 -15 3.35 0.3654
WVFGRD96 12.0 40 35 -10 3.36 0.3925
WVFGRD96 14.0 40 35 -10 3.38 0.4176
WVFGRD96 16.0 45 40 -5 3.40 0.4388
WVFGRD96 18.0 60 35 25 3.42 0.4577
WVFGRD96 20.0 65 30 30 3.43 0.4701
WVFGRD96 22.0 70 30 35 3.46 0.4816
WVFGRD96 24.0 70 30 35 3.48 0.4860
WVFGRD96 26.0 75 30 45 3.50 0.4902
WVFGRD96 28.0 75 30 45 3.51 0.4842
WVFGRD96 30.0 75 30 45 3.52 0.4779
WVFGRD96 32.0 75 30 45 3.53 0.4638
WVFGRD96 34.0 70 30 40 3.54 0.4501
WVFGRD96 36.0 30 40 -45 3.56 0.4335
WVFGRD96 38.0 35 45 -35 3.56 0.4235
WVFGRD96 40.0 30 40 -40 3.68 0.4166
WVFGRD96 42.0 30 40 -35 3.68 0.4086
WVFGRD96 44.0 30 40 -35 3.69 0.4039
WVFGRD96 46.0 35 45 -30 3.70 0.3978
WVFGRD96 48.0 45 30 0 3.69 0.3989
WVFGRD96 50.0 45 30 0 3.70 0.3984
WVFGRD96 52.0 45 30 0 3.71 0.3982
WVFGRD96 54.0 45 30 0 3.72 0.3988
WVFGRD96 56.0 45 30 0 3.73 0.3985
WVFGRD96 58.0 40 30 -5 3.74 0.3972
WVFGRD96 60.0 40 30 -5 3.75 0.3959
WVFGRD96 62.0 85 35 45 3.77 0.4018
WVFGRD96 64.0 90 35 50 3.78 0.4090
WVFGRD96 66.0 90 35 50 3.79 0.4148
WVFGRD96 68.0 90 35 50 3.79 0.4202
WVFGRD96 70.0 85 35 50 3.80 0.4302
WVFGRD96 72.0 85 35 50 3.81 0.4391
WVFGRD96 74.0 105 35 80 3.83 0.4549
WVFGRD96 76.0 295 55 95 3.84 0.4727
WVFGRD96 78.0 105 35 80 3.84 0.4905
WVFGRD96 80.0 105 35 80 3.85 0.5071
WVFGRD96 82.0 105 35 80 3.86 0.5228
WVFGRD96 84.0 105 35 80 3.87 0.5385
WVFGRD96 86.0 105 35 80 3.87 0.5527
WVFGRD96 88.0 105 35 80 3.88 0.5661
WVFGRD96 90.0 100 35 75 3.88 0.5789
WVFGRD96 92.0 100 35 75 3.89 0.5907
WVFGRD96 94.0 100 35 75 3.89 0.6011
WVFGRD96 96.0 100 35 75 3.90 0.6114
WVFGRD96 98.0 100 40 70 3.91 0.6204
WVFGRD96 100.0 100 40 70 3.92 0.6290
WVFGRD96 102.0 100 40 70 3.92 0.6371
WVFGRD96 104.0 100 40 70 3.92 0.6444
WVFGRD96 106.0 100 40 70 3.93 0.6503
WVFGRD96 108.0 100 40 70 3.93 0.6556
WVFGRD96 110.0 100 40 70 3.94 0.6601
WVFGRD96 112.0 100 40 70 3.94 0.6645
WVFGRD96 114.0 95 40 65 3.94 0.6677
WVFGRD96 116.0 95 40 65 3.95 0.6708
WVFGRD96 118.0 95 40 65 3.95 0.6725
WVFGRD96 120.0 95 40 65 3.95 0.6746
WVFGRD96 122.0 95 40 65 3.96 0.6754
WVFGRD96 124.0 95 40 65 3.96 0.6763
WVFGRD96 126.0 95 40 65 3.96 0.6766
WVFGRD96 128.0 95 40 65 3.97 0.6765
WVFGRD96 130.0 95 40 65 3.97 0.6755
WVFGRD96 132.0 95 40 65 3.97 0.6751
WVFGRD96 134.0 95 40 65 3.98 0.6742
WVFGRD96 136.0 95 40 65 3.98 0.6726
WVFGRD96 138.0 95 40 65 3.98 0.6711
The best solution is
WVFGRD96 126.0 95 40 65 3.96 0.6766
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 80 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