The ANSS event ID is ak014437mao9 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak014437mao9/executive.
2014/03/30 01:32:54 62.219 -151.222 82.3 5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2014/03/30 01:32:54:0 62.22 -151.22 82.3 5.0 Alaska
Stations used:
AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ
AK.CTG AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN
AK.KNK AK.KTH AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA AK.PPLA
AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCRK AK.SKN AK.SSN
AK.SWD AK.TGL AK.TRF AK.VRDI AK.WRH AT.MENT AT.PMR AT.SVW2
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 = 3.35e+23 dyne-cm
Mw = 4.95
Z = 88 km
Plane Strike Dip Rake
NP1 351 85 120
NP2 90 30 10
Principal Axes:
Axis Value Plunge Azimuth
T 3.35e+23 42 290
N 0.00e+00 29 168
P -3.35e+23 33 57
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.04e+22
Mxy -1.65e+23
Mxz -2.91e+22
Myy -1.44e+16
Myz -2.86e+23
Mzz 5.04e+22
####----------
#########-------------
############----------------
##############----------------
################------------------
#################----------- -----
###################---------- P ------
####### ##########---------- -------
####### T ###########-------------------
######## ###########--------------------
######################--------------------
-#####################-------------------#
-######################------------------#
-#####################-----------------#
---###################---------------###
---##################--------------###
----#################-----------####
------##############--------######
---------#########---#########
-----------------###########
--------------########
----------####
Global CMT Convention Moment Tensor:
R T P
5.04e+22 -2.91e+22 2.86e+23
-2.91e+22 -5.04e+22 1.65e+23
2.86e+23 1.65e+23 -1.44e+16
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140330013254/index.html
|
STK = 90
DIP = 30
RAKE = 10
MW = 4.95
HS = 88.0
The NDK file is 20140330013254.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 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 70 65 -20 4.12 0.2554
WVFGRD96 4.0 75 85 5 4.19 0.2986
WVFGRD96 6.0 255 90 -10 4.25 0.3223
WVFGRD96 8.0 255 90 -15 4.30 0.3421
WVFGRD96 10.0 75 80 15 4.33 0.3572
WVFGRD96 12.0 75 80 15 4.35 0.3646
WVFGRD96 14.0 75 80 15 4.38 0.3709
WVFGRD96 16.0 75 80 15 4.40 0.3774
WVFGRD96 18.0 75 80 15 4.42 0.3846
WVFGRD96 20.0 75 80 15 4.44 0.3927
WVFGRD96 22.0 75 80 10 4.46 0.4019
WVFGRD96 24.0 75 80 10 4.48 0.4127
WVFGRD96 26.0 75 80 10 4.50 0.4238
WVFGRD96 28.0 75 75 10 4.52 0.4344
WVFGRD96 30.0 75 75 10 4.54 0.4449
WVFGRD96 32.0 75 75 10 4.57 0.4562
WVFGRD96 34.0 75 75 10 4.59 0.4689
WVFGRD96 36.0 75 80 10 4.62 0.4849
WVFGRD96 38.0 75 80 10 4.66 0.5045
WVFGRD96 40.0 75 80 15 4.71 0.5246
WVFGRD96 42.0 75 75 10 4.73 0.5338
WVFGRD96 44.0 75 75 10 4.75 0.5436
WVFGRD96 46.0 75 70 10 4.76 0.5518
WVFGRD96 48.0 80 60 5 4.77 0.5621
WVFGRD96 50.0 75 55 0 4.79 0.5801
WVFGRD96 52.0 80 55 5 4.80 0.5996
WVFGRD96 54.0 80 50 5 4.82 0.6193
WVFGRD96 56.0 80 50 5 4.83 0.6390
WVFGRD96 58.0 80 45 5 4.84 0.6560
WVFGRD96 60.0 80 45 5 4.86 0.6738
WVFGRD96 62.0 80 45 5 4.86 0.6884
WVFGRD96 64.0 80 45 5 4.87 0.7029
WVFGRD96 66.0 80 40 5 4.89 0.7153
WVFGRD96 68.0 80 40 5 4.89 0.7258
WVFGRD96 70.0 80 40 5 4.90 0.7342
WVFGRD96 72.0 85 40 10 4.90 0.7437
WVFGRD96 74.0 85 35 10 4.91 0.7521
WVFGRD96 76.0 85 35 5 4.92 0.7588
WVFGRD96 78.0 85 35 5 4.93 0.7642
WVFGRD96 80.0 90 35 10 4.93 0.7681
WVFGRD96 82.0 90 30 10 4.94 0.7717
WVFGRD96 84.0 90 30 10 4.95 0.7745
WVFGRD96 86.0 90 30 10 4.95 0.7753
WVFGRD96 88.0 90 30 10 4.95 0.7754
WVFGRD96 90.0 90 30 10 4.96 0.7738
WVFGRD96 92.0 95 30 10 4.97 0.7722
WVFGRD96 94.0 95 30 10 4.97 0.7704
WVFGRD96 96.0 95 30 10 4.98 0.7673
WVFGRD96 98.0 95 30 10 4.98 0.7633
WVFGRD96 100.0 95 30 10 4.98 0.7597
WVFGRD96 102.0 95 30 10 4.98 0.7550
WVFGRD96 104.0 95 30 10 4.99 0.7494
WVFGRD96 106.0 100 25 15 4.99 0.7421
WVFGRD96 108.0 100 25 15 4.99 0.7357
WVFGRD96 110.0 100 25 15 4.99 0.7305
WVFGRD96 112.0 100 25 10 5.01 0.7243
WVFGRD96 114.0 100 25 10 5.01 0.7168
WVFGRD96 116.0 100 25 10 5.01 0.7088
WVFGRD96 118.0 105 25 15 5.01 0.7024
WVFGRD96 120.0 105 25 15 5.01 0.6954
WVFGRD96 122.0 105 25 15 5.01 0.6865
WVFGRD96 124.0 105 25 15 5.02 0.6803
WVFGRD96 126.0 105 25 15 5.02 0.6725
WVFGRD96 128.0 105 25 15 5.02 0.6630
The best solution is
WVFGRD96 88.0 90 30 10 4.95 0.7754
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 a -30 a 180 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