The ANSS event ID is ak014768f0z7 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak014768f0z7/executive.
2014/06/05 14:41:14 62.842 -149.405 78.8 3.9 Arkansas
USGS/SLU Moment Tensor Solution
ENS 2014/06/05 14:41:14:0 62.84 -149.40 78.8 3.9 Arkansas
Stations used:
AK.CCB AK.DHY AK.GHO AK.GLI AK.HARP AK.HDA AK.KTH AK.MCK
AK.PPLA AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.TRF AK.WRH
AT.PMR IM.IL31 IU.COLA
Filtering commands used:
cut a -30 a 100
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.02e+22 dyne-cm
Mw = 3.94
Z = 89 km
Plane Strike Dip Rake
NP1 85 90 -10
NP2 175 80 -180
Principal Axes:
Axis Value Plunge Azimuth
T 1.02e+22 7 130
N 0.00e+00 80 265
P -1.02e+22 7 40
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.75e+21
Mxy -9.92e+21
Mxz -1.77e+21
Myy 1.75e+21
Myz 1.55e+20
Mzz 1.55e+14
#####---------
#########------------
###########------------- P -
############------------- --
##############--------------------
###############---------------------
################----------------------
#################-----------------------
#################-----------------------
##################------------------------
##################--------------##########
##########---------#######################
-------------------#######################
------------------######################
------------------######################
-----------------#####################
-----------------############### #
----------------############### T
---------------##############
--------------##############
------------##########
--------######
Global CMT Convention Moment Tensor:
R T P
1.55e+14 -1.77e+21 -1.55e+20
-1.77e+21 -1.75e+21 9.92e+21
-1.55e+20 9.92e+21 1.75e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140605144114/index.html
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STK = 85
DIP = 90
RAKE = -10
MW = 3.94
HS = 89.0
The NDK file is 20140605144114.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 100 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 -5 80 -5 3.16 0.3248
WVFGRD96 4.0 -5 80 -5 3.24 0.3712
WVFGRD96 6.0 355 80 -15 3.30 0.3856
WVFGRD96 8.0 355 75 -15 3.35 0.3935
WVFGRD96 9.0 265 85 -5 3.36 0.4051
WVFGRD96 10.0 85 90 5 3.38 0.4164
WVFGRD96 12.0 85 90 5 3.42 0.4303
WVFGRD96 14.0 265 85 -5 3.44 0.4390
WVFGRD96 16.0 265 90 0 3.47 0.4466
WVFGRD96 18.0 85 90 0 3.49 0.4532
WVFGRD96 19.0 265 85 -5 3.50 0.4592
WVFGRD96 20.0 265 85 -5 3.51 0.4639
WVFGRD96 22.0 265 75 5 3.53 0.4743
WVFGRD96 24.0 265 75 5 3.55 0.4856
WVFGRD96 26.0 265 75 5 3.56 0.4952
WVFGRD96 28.0 265 75 5 3.58 0.5025
WVFGRD96 29.0 265 80 10 3.59 0.5070
WVFGRD96 30.0 270 80 10 3.60 0.5111
WVFGRD96 32.0 270 80 10 3.62 0.5181
WVFGRD96 34.0 265 80 10 3.64 0.5231
WVFGRD96 36.0 265 80 10 3.66 0.5263
WVFGRD96 38.0 265 90 5 3.70 0.5341
WVFGRD96 39.0 265 90 5 3.71 0.5398
WVFGRD96 40.0 265 90 5 3.73 0.5458
WVFGRD96 42.0 270 80 10 3.76 0.5428
WVFGRD96 44.0 270 80 10 3.77 0.5431
WVFGRD96 46.0 85 80 -10 3.79 0.5478
WVFGRD96 48.0 85 80 -10 3.80 0.5539
WVFGRD96 49.0 85 80 -10 3.81 0.5575
WVFGRD96 50.0 85 80 -10 3.81 0.5614
WVFGRD96 52.0 85 80 -10 3.83 0.5691
WVFGRD96 54.0 85 80 -10 3.84 0.5770
WVFGRD96 56.0 85 80 -10 3.85 0.5854
WVFGRD96 58.0 85 80 -15 3.86 0.5930
WVFGRD96 59.0 85 85 -10 3.86 0.5962
WVFGRD96 60.0 85 85 -10 3.86 0.6004
WVFGRD96 62.0 85 85 -10 3.87 0.6071
WVFGRD96 64.0 85 85 -10 3.88 0.6137
WVFGRD96 66.0 85 85 -10 3.88 0.6190
WVFGRD96 68.0 85 85 -10 3.89 0.6245
WVFGRD96 69.0 265 90 10 3.89 0.6246
WVFGRD96 70.0 85 85 -10 3.89 0.6285
WVFGRD96 72.0 85 85 -10 3.90 0.6317
WVFGRD96 74.0 265 90 10 3.91 0.6349
WVFGRD96 76.0 85 90 -10 3.91 0.6378
WVFGRD96 78.0 85 90 -10 3.92 0.6397
WVFGRD96 79.0 85 90 -10 3.92 0.6408
WVFGRD96 80.0 85 90 -10 3.92 0.6422
WVFGRD96 82.0 85 90 -10 3.92 0.6431
WVFGRD96 84.0 85 90 -10 3.93 0.6441
WVFGRD96 86.0 85 90 -10 3.93 0.6451
WVFGRD96 88.0 85 90 -10 3.94 0.6453
WVFGRD96 89.0 85 90 -10 3.94 0.6455
WVFGRD96 90.0 85 90 -10 3.94 0.6453
WVFGRD96 92.0 85 90 -10 3.95 0.6444
WVFGRD96 94.0 85 90 -10 3.95 0.6439
WVFGRD96 96.0 265 85 10 3.96 0.6445
WVFGRD96 98.0 85 90 -10 3.96 0.6433
WVFGRD96 99.0 265 85 10 3.96 0.6436
WVFGRD96 100.0 265 85 10 3.97 0.6440
WVFGRD96 102.0 85 90 -10 3.97 0.6413
WVFGRD96 104.0 85 90 -10 3.97 0.6399
WVFGRD96 106.0 85 90 -5 3.97 0.6385
WVFGRD96 108.0 85 90 -5 3.97 0.6370
WVFGRD96 109.0 265 85 5 3.98 0.6384
WVFGRD96 110.0 85 90 -5 3.98 0.6353
WVFGRD96 112.0 85 90 -5 3.98 0.6333
WVFGRD96 114.0 85 90 -5 3.99 0.6323
WVFGRD96 116.0 85 90 -5 3.99 0.6310
WVFGRD96 118.0 85 90 -5 3.99 0.6292
WVFGRD96 119.0 265 85 5 4.00 0.6310
The best solution is
WVFGRD96 89.0 85 90 -10 3.94 0.6455
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 100 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