The ANSS event ID is ak0138gmedul and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0138gmedul/executive.
2013/07/03 19:34:01 62.160 -149.500 49.9 3.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/07/03 19:34:01:0 62.16 -149.50 49.9 3.8 Alaska
Stations used:
AK.CAST AK.DHY AK.DOT AK.GLI AK.HIN AK.KNK AK.KTH AK.MCK
AK.PPLA AK.RC01 AK.RIDG AK.SCM AK.TRF AK.WAT1 AK.WAT2
AK.WAT3 AK.WAT4 AT.PMR IU.COLA
Filtering commands used:
cut a -10 a 110
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 7.24e+21 dyne-cm
Mw = 3.84
Z = 60 km
Plane Strike Dip Rake
NP1 205 65 -45
NP2 318 50 -147
Principal Axes:
Axis Value Plunge Azimuth
T 7.24e+21 9 265
N 0.00e+00 40 2
P -7.24e+21 49 164
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.86e+21
Mxy 1.48e+21
Mxz 3.35e+21
Myy 6.78e+21
Myz -2.07e+21
Mzz -3.92e+21
--------------
-----------------#####
------------------##########
#############----#############
#################-################
#################-----##############
################---------#############
################------------############
###############--------------###########
###############----------------###########
###########-------------------#########
T ###########-------------------#########
##########---------------------########
############----------------------######
###########-----------------------######
##########---------- -----------####
#########---------- P -----------###
#######----------- -----------##
#####------------------------#
#####-----------------------
##--------------------
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Global CMT Convention Moment Tensor:
R T P
-3.92e+21 3.35e+21 2.07e+21
3.35e+21 -2.86e+21 -1.48e+21
2.07e+21 -1.48e+21 6.78e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130703193401/index.html
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STK = 205
DIP = 65
RAKE = -45
MW = 3.84
HS = 60.0
The NDK file is 20130703193401.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 -10 a 110 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 90 45 -85 2.81 0.1773
WVFGRD96 1.0 105 45 -65 2.84 0.1481
WVFGRD96 2.0 95 45 -80 3.00 0.1988
WVFGRD96 3.0 285 70 5 3.00 0.1760
WVFGRD96 4.0 320 65 30 3.09 0.2024
WVFGRD96 5.0 320 65 30 3.12 0.2391
WVFGRD96 6.0 320 65 30 3.15 0.2686
WVFGRD96 7.0 320 65 30 3.17 0.2905
WVFGRD96 8.0 320 65 30 3.24 0.3093
WVFGRD96 9.0 320 65 30 3.26 0.3215
WVFGRD96 10.0 320 65 30 3.27 0.3275
WVFGRD96 11.0 320 60 30 3.28 0.3299
WVFGRD96 12.0 320 60 30 3.30 0.3308
WVFGRD96 13.0 320 60 30 3.31 0.3335
WVFGRD96 14.0 320 60 30 3.32 0.3340
WVFGRD96 15.0 320 60 30 3.34 0.3324
WVFGRD96 16.0 320 60 30 3.35 0.3288
WVFGRD96 17.0 320 60 30 3.36 0.3237
WVFGRD96 18.0 320 60 30 3.37 0.3159
WVFGRD96 19.0 320 60 30 3.38 0.3081
WVFGRD96 20.0 320 60 30 3.39 0.2982
WVFGRD96 21.0 325 60 35 3.40 0.2845
WVFGRD96 22.0 325 55 35 3.40 0.2724
WVFGRD96 23.0 90 40 15 3.39 0.2627
WVFGRD96 24.0 95 35 20 3.40 0.2599
WVFGRD96 25.0 50 65 20 3.43 0.2559
WVFGRD96 26.0 50 65 20 3.44 0.2524
WVFGRD96 27.0 220 75 -25 3.48 0.2535
WVFGRD96 28.0 220 75 -25 3.49 0.2577
WVFGRD96 29.0 220 70 -30 3.49 0.2595
WVFGRD96 30.0 220 65 -30 3.49 0.2697
WVFGRD96 31.0 220 65 -30 3.51 0.2903
WVFGRD96 32.0 220 70 -30 3.53 0.3087
WVFGRD96 33.0 215 65 -35 3.54 0.3261
WVFGRD96 34.0 215 65 -35 3.55 0.3433
WVFGRD96 35.0 215 70 -35 3.57 0.3575
WVFGRD96 36.0 215 70 -35 3.58 0.3680
WVFGRD96 37.0 215 70 -35 3.59 0.3780
WVFGRD96 38.0 215 70 -35 3.60 0.3856
WVFGRD96 39.0 215 65 -35 3.61 0.3915
WVFGRD96 40.0 210 65 -40 3.71 0.3978
WVFGRD96 41.0 210 65 -45 3.72 0.4108
WVFGRD96 42.0 210 65 -45 3.73 0.4218
WVFGRD96 43.0 210 65 -45 3.74 0.4304
WVFGRD96 44.0 210 65 -45 3.75 0.4370
WVFGRD96 45.0 210 65 -45 3.76 0.4432
WVFGRD96 46.0 210 65 -45 3.76 0.4489
WVFGRD96 47.0 210 65 -45 3.77 0.4537
WVFGRD96 48.0 210 65 -45 3.78 0.4575
WVFGRD96 49.0 210 65 -45 3.78 0.4616
WVFGRD96 50.0 205 65 -45 3.80 0.4642
WVFGRD96 51.0 205 65 -45 3.80 0.4669
WVFGRD96 52.0 205 65 -45 3.81 0.4697
WVFGRD96 53.0 205 65 -45 3.81 0.4724
WVFGRD96 54.0 205 65 -45 3.82 0.4746
WVFGRD96 55.0 205 65 -45 3.82 0.4765
WVFGRD96 56.0 205 65 -45 3.83 0.4773
WVFGRD96 57.0 205 65 -45 3.83 0.4788
WVFGRD96 58.0 205 65 -45 3.84 0.4791
WVFGRD96 59.0 205 65 -45 3.84 0.4787
WVFGRD96 60.0 205 65 -45 3.84 0.4793
WVFGRD96 61.0 205 65 -45 3.85 0.4779
WVFGRD96 62.0 205 65 -45 3.85 0.4774
WVFGRD96 63.0 205 70 -45 3.86 0.4763
WVFGRD96 64.0 205 70 -45 3.86 0.4763
WVFGRD96 65.0 205 70 -45 3.87 0.4766
WVFGRD96 66.0 205 70 -45 3.87 0.4762
WVFGRD96 67.0 205 70 -40 3.88 0.4740
WVFGRD96 68.0 205 70 -40 3.88 0.4739
WVFGRD96 69.0 205 70 -40 3.88 0.4733
WVFGRD96 70.0 205 70 -40 3.89 0.4715
WVFGRD96 71.0 205 70 -40 3.89 0.4694
WVFGRD96 72.0 205 70 -40 3.89 0.4682
WVFGRD96 73.0 205 70 -40 3.90 0.4661
WVFGRD96 74.0 205 70 -40 3.90 0.4637
WVFGRD96 75.0 205 70 -40 3.90 0.4610
WVFGRD96 76.0 205 70 -40 3.91 0.4585
WVFGRD96 77.0 205 70 -40 3.91 0.4557
WVFGRD96 78.0 205 70 -40 3.91 0.4525
WVFGRD96 79.0 205 70 -40 3.91 0.4493
The best solution is
WVFGRD96 60.0 205 65 -45 3.84 0.4793
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 -10 a 110 rtr taper w 0.1 hp c 0.02 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