The ANSS event ID is ak014cn5hnbt and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak014cn5hnbt/executive.
2014/10/02 21:33:15 63.055 -150.775 123.6 4.3 Alaska
USGS/SLU Moment Tensor Solution
ENS 2014/10/02 21:33:15:0 63.06 -150.77 123.6 4.3 Alaska
Stations used:
AK.BPAW AK.BWN AK.CRQ AK.DHY AK.DOT AK.EYAK AK.FID AK.GHO
AK.GLB AK.GLI AK.HDA AK.HIN AK.KLU AK.KNK AK.KTH AK.MCAR
AK.MDM AK.PAX AK.PPLA AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN
AK.SSN AK.SWD AK.TRF AK.WRH IM.IL31 IU.COLA TA.M24K
Filtering commands used:
cut o DIST/3.3 -50 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.55e+22 dyne-cm
Mw = 4.30
Z = 122 km
Plane Strike Dip Rake
NP1 50 70 85
NP2 244 21 103
Principal Axes:
Axis Value Plunge Azimuth
T 3.55e+22 65 312
N 0.00e+00 5 52
P -3.55e+22 25 144
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.62e+22
Mxy 1.07e+22
Mxz 2.01e+22
Myy -6.53e+21
Myz -1.82e+22
Mzz 2.27e+22
--------------
----------------------
--------################----
------#######################-
-----#############################
----#############################---
----#############################-----
---########### ################-------
--############ T ##############---------
---############ #############-----------
--###########################-------------
--##########################--------------
--########################----------------
-#####################------------------
-###################--------------------
################----------------------
############-------------- -------
#######------------------ P ------
----------------------- ----
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.27e+22 2.01e+22 1.82e+22
2.01e+22 -1.62e+22 -1.07e+22
1.82e+22 -1.07e+22 -6.53e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141002213315/index.html
|
STK = 50
DIP = 70
RAKE = 85
MW = 4.30
HS = 122.0
The NDK file is 20141002213315.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.
 |
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.
|
|
|
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/3.3 -50 o DIST/3.3 +60 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 2.0 240 50 -90 3.48 0.1780
WVFGRD96 4.0 70 35 -75 3.58 0.1646
WVFGRD96 6.0 60 30 -80 3.58 0.1381
WVFGRD96 8.0 60 30 -80 3.66 0.1560
WVFGRD96 10.0 70 30 -70 3.63 0.1468
WVFGRD96 12.0 30 30 75 3.64 0.1634
WVFGRD96 14.0 30 40 75 3.67 0.1840
WVFGRD96 16.0 30 40 70 3.67 0.2019
WVFGRD96 18.0 30 45 70 3.69 0.2154
WVFGRD96 20.0 30 45 70 3.70 0.2257
WVFGRD96 22.0 30 45 70 3.71 0.2317
WVFGRD96 24.0 30 45 70 3.72 0.2352
WVFGRD96 26.0 30 45 70 3.73 0.2365
WVFGRD96 28.0 25 45 65 3.74 0.2358
WVFGRD96 30.0 25 45 65 3.75 0.2337
WVFGRD96 32.0 25 45 65 3.76 0.2302
WVFGRD96 34.0 30 40 70 3.77 0.2255
WVFGRD96 36.0 10 40 65 3.79 0.2199
WVFGRD96 38.0 20 55 75 3.82 0.2155
WVFGRD96 40.0 20 60 80 3.97 0.2142
WVFGRD96 42.0 25 60 85 3.99 0.2151
WVFGRD96 44.0 25 60 80 3.99 0.2159
WVFGRD96 46.0 30 55 80 4.00 0.2169
WVFGRD96 48.0 25 60 75 4.00 0.2201
WVFGRD96 50.0 25 60 70 4.01 0.2241
WVFGRD96 52.0 10 60 25 4.00 0.2331
WVFGRD96 54.0 15 60 30 4.01 0.2457
WVFGRD96 56.0 15 60 25 4.04 0.2597
WVFGRD96 58.0 15 60 25 4.06 0.2753
WVFGRD96 60.0 20 60 25 4.07 0.2929
WVFGRD96 62.0 35 75 80 4.10 0.3248
WVFGRD96 64.0 35 75 80 4.12 0.3609
WVFGRD96 66.0 40 70 80 4.14 0.3976
WVFGRD96 68.0 40 75 75 4.15 0.4351
WVFGRD96 70.0 45 70 80 4.17 0.4686
WVFGRD96 72.0 45 70 80 4.18 0.4937
WVFGRD96 74.0 45 70 80 4.19 0.5106
WVFGRD96 76.0 45 70 85 4.20 0.5269
WVFGRD96 78.0 240 20 100 4.21 0.5416
WVFGRD96 80.0 45 70 85 4.22 0.5575
WVFGRD96 82.0 240 20 100 4.22 0.5720
WVFGRD96 84.0 50 70 85 4.23 0.5836
WVFGRD96 86.0 50 70 85 4.23 0.5966
WVFGRD96 88.0 50 70 90 4.24 0.6071
WVFGRD96 90.0 50 70 90 4.25 0.6170
WVFGRD96 92.0 50 70 90 4.25 0.6258
WVFGRD96 94.0 50 65 80 4.25 0.6327
WVFGRD96 96.0 50 65 80 4.25 0.6423
WVFGRD96 98.0 50 65 80 4.26 0.6498
WVFGRD96 100.0 50 65 80 4.26 0.6567
WVFGRD96 102.0 50 65 80 4.27 0.6623
WVFGRD96 104.0 50 65 80 4.27 0.6673
WVFGRD96 106.0 50 70 85 4.28 0.6717
WVFGRD96 108.0 50 70 85 4.28 0.6754
WVFGRD96 110.0 50 70 85 4.28 0.6788
WVFGRD96 112.0 50 70 85 4.29 0.6814
WVFGRD96 114.0 50 70 85 4.29 0.6838
WVFGRD96 116.0 50 70 85 4.29 0.6848
WVFGRD96 118.0 50 70 85 4.29 0.6864
WVFGRD96 120.0 50 70 85 4.30 0.6864
WVFGRD96 122.0 50 70 85 4.30 0.6867
WVFGRD96 124.0 235 20 95 4.30 0.6856
WVFGRD96 126.0 235 20 95 4.31 0.6847
WVFGRD96 128.0 50 70 85 4.30 0.6842
WVFGRD96 130.0 50 70 85 4.31 0.6822
WVFGRD96 132.0 50 70 85 4.31 0.6816
WVFGRD96 134.0 50 70 85 4.31 0.6793
WVFGRD96 136.0 50 70 85 4.31 0.6775
WVFGRD96 138.0 55 70 90 4.32 0.6751
WVFGRD96 140.0 240 20 95 4.32 0.6731
WVFGRD96 142.0 240 20 95 4.32 0.6709
WVFGRD96 144.0 55 70 90 4.33 0.6673
WVFGRD96 146.0 55 70 90 4.33 0.6648
WVFGRD96 148.0 55 70 90 4.33 0.6619
The best solution is
WVFGRD96 122.0 50 70 85 4.30 0.6867
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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/3.3 -50 o DIST/3.3 +60 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3
|
| 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. |
|
| 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