Location
2012/08/29 12:50:55 60.314 -150.712 58.7 4.40 Alaska
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports main page
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2012/08/29 12:50:55:0 60.31 -150.71 58.7 4.4 Alaska
Stations used:
AK.BMR AK.BPAW AK.BRLK AK.CNP AK.DOT AK.FIB AK.FID AK.GHO
AK.GLI AK.HIN AK.HOM AK.KNK AK.KTH AK.RC01 AK.RIDG AK.SAW
AK.SCM AK.SKN AK.SSN AT.SVW2 II.KDAK IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 7.85e+22 dyne-cm
Mw = 4.53
Z = 72 km
Plane Strike Dip Rake
NP1 281 72 154
NP2 20 65 20
Principal Axes:
Axis Value Plunge Azimuth
T 7.85e+22 31 239
N 0.00e+00 58 69
P -7.85e+22 5 332
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.54e+22
Mxy 5.78e+22
Mxz -2.34e+22
Myy 2.48e+22
Myz -2.69e+22
Mzz 2.06e+22
--------------
P ----------------###
--- ----------------######
-----------------------#######
--------------------------########
---------------------------#########
---------------------------###########
----------------------------############
-###################--------############
############################-#############
############################------########
###########################----------#####
###########################-------------##
###### ################---------------
###### T ###############----------------
##### ##############----------------
####################----------------
##################----------------
###############---------------
############----------------
#######---------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.06e+22 -2.34e+22 2.69e+22
-2.34e+22 -4.54e+22 -5.78e+22
2.69e+22 -5.78e+22 2.48e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120829125055/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 20
DIP = 65
RAKE = 20
MW = 4.53
HS = 72.0
The NDK file is 20120829125055.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMT |
USGS/SLU Moment Tensor Solution
ENS 2012/08/29 12:50:55:0 60.31 -150.71 58.7 4.4 Alaska
Stations used:
AK.BMR AK.BPAW AK.BRLK AK.CNP AK.DOT AK.FIB AK.FID AK.GHO
AK.GLI AK.HIN AK.HOM AK.KNK AK.KTH AK.RC01 AK.RIDG AK.SAW
AK.SCM AK.SKN AK.SSN AT.SVW2 II.KDAK IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 7.85e+22 dyne-cm
Mw = 4.53
Z = 72 km
Plane Strike Dip Rake
NP1 281 72 154
NP2 20 65 20
Principal Axes:
Axis Value Plunge Azimuth
T 7.85e+22 31 239
N 0.00e+00 58 69
P -7.85e+22 5 332
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.54e+22
Mxy 5.78e+22
Mxz -2.34e+22
Myy 2.48e+22
Myz -2.69e+22
Mzz 2.06e+22
--------------
P ----------------###
--- ----------------######
-----------------------#######
--------------------------########
---------------------------#########
---------------------------###########
----------------------------############
-###################--------############
############################-#############
############################------########
###########################----------#####
###########################-------------##
###### ################---------------
###### T ###############----------------
##### ##############----------------
####################----------------
##################----------------
###############---------------
############----------------
#######---------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.06e+22 -2.34e+22 2.69e+22
-2.34e+22 -4.54e+22 -5.78e+22
2.69e+22 -5.78e+22 2.48e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120829125055/index.html
|
USGS/SLU Regional Moment Solution
12/08/29 12:50:51.00
Epicenter: 60.269 -150.709
MW 4.5
USGS/SLU REGIONAL MOMENT TENSOR
Depth 67 No. of sta: 53
Moment Tensor; Scale 10**15 Nm
Mrr= 1.50 Mtt=-3.34
Mpp= 1.84 Mrt=-2.69
Mrp= 3.18 Mtp=-4.53
Principal axes:
T Val= 7.36 Plg=35 Azm=238
N -1.30 54 72
P -6.06 7 333
Best Double Couple:Mo=6.8*10**15
NP1:Strike= 21 Dip=60 Slip= 22
NP2: 280 71 149
|
Magnitudes
ML Magnitude
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
Context
The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).
Waveform Inversion
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the
and stations used for the waveform inversion are shown in the next figure.
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Location of broadband stations used for waveform inversion
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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 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:
hp c 0.02 n 3
lp c 0.06 n 3
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 10 65 -25 3.66 0.1594
WVFGRD96 1.0 25 85 5 3.66 0.1720
WVFGRD96 2.0 25 75 15 3.79 0.2303
WVFGRD96 3.0 25 65 10 3.85 0.2540
WVFGRD96 4.0 20 65 -5 3.87 0.2769
WVFGRD96 5.0 20 65 -5 3.90 0.2979
WVFGRD96 6.0 20 65 -5 3.93 0.3151
WVFGRD96 7.0 20 70 -5 3.95 0.3302
WVFGRD96 8.0 20 65 -10 3.99 0.3432
WVFGRD96 9.0 20 65 -10 4.00 0.3530
WVFGRD96 10.0 20 65 -10 4.01 0.3604
WVFGRD96 11.0 20 70 -15 4.03 0.3670
WVFGRD96 12.0 20 70 -15 4.05 0.3725
WVFGRD96 13.0 20 70 -15 4.06 0.3767
WVFGRD96 14.0 20 70 -15 4.07 0.3799
WVFGRD96 15.0 20 70 -15 4.08 0.3831
WVFGRD96 16.0 15 70 -20 4.09 0.3868
WVFGRD96 17.0 15 70 -20 4.10 0.3900
WVFGRD96 18.0 15 70 -20 4.11 0.3932
WVFGRD96 19.0 15 70 -20 4.12 0.3966
WVFGRD96 20.0 15 70 -20 4.13 0.3998
WVFGRD96 21.0 15 70 -20 4.14 0.4024
WVFGRD96 22.0 15 70 -15 4.14 0.4048
WVFGRD96 23.0 15 70 -20 4.15 0.4070
WVFGRD96 24.0 15 70 -15 4.16 0.4098
WVFGRD96 25.0 15 70 -15 4.17 0.4121
WVFGRD96 26.0 15 70 -15 4.17 0.4141
WVFGRD96 27.0 15 70 -10 4.18 0.4158
WVFGRD96 28.0 15 70 -10 4.19 0.4173
WVFGRD96 29.0 15 70 -10 4.20 0.4190
WVFGRD96 30.0 15 70 -10 4.20 0.4204
WVFGRD96 31.0 15 70 -10 4.21 0.4214
WVFGRD96 32.0 15 70 -5 4.22 0.4219
WVFGRD96 33.0 15 70 -5 4.23 0.4221
WVFGRD96 34.0 15 70 -5 4.24 0.4220
WVFGRD96 35.0 15 70 0 4.25 0.4231
WVFGRD96 36.0 15 70 0 4.26 0.4247
WVFGRD96 37.0 15 70 0 4.27 0.4262
WVFGRD96 38.0 15 70 0 4.28 0.4275
WVFGRD96 39.0 15 70 0 4.29 0.4284
WVFGRD96 40.0 15 60 5 4.34 0.4300
WVFGRD96 41.0 15 60 5 4.35 0.4305
WVFGRD96 42.0 15 60 5 4.35 0.4309
WVFGRD96 43.0 15 65 5 4.36 0.4313
WVFGRD96 44.0 15 65 5 4.37 0.4319
WVFGRD96 45.0 15 65 10 4.38 0.4327
WVFGRD96 46.0 15 65 10 4.39 0.4334
WVFGRD96 47.0 20 65 15 4.40 0.4345
WVFGRD96 48.0 20 65 15 4.40 0.4362
WVFGRD96 49.0 20 65 20 4.42 0.4388
WVFGRD96 50.0 20 65 20 4.42 0.4422
WVFGRD96 51.0 20 65 20 4.43 0.4453
WVFGRD96 52.0 20 65 20 4.44 0.4483
WVFGRD96 53.0 20 65 20 4.44 0.4513
WVFGRD96 54.0 20 65 20 4.45 0.4545
WVFGRD96 55.0 20 65 20 4.46 0.4573
WVFGRD96 56.0 20 65 20 4.46 0.4598
WVFGRD96 57.0 20 65 20 4.47 0.4625
WVFGRD96 58.0 20 65 20 4.47 0.4655
WVFGRD96 59.0 20 65 20 4.48 0.4679
WVFGRD96 60.0 20 65 20 4.48 0.4694
WVFGRD96 61.0 20 65 20 4.49 0.4711
WVFGRD96 62.0 20 65 20 4.49 0.4735
WVFGRD96 63.0 20 65 20 4.50 0.4748
WVFGRD96 64.0 20 65 20 4.50 0.4760
WVFGRD96 65.0 20 65 20 4.50 0.4774
WVFGRD96 66.0 20 65 20 4.51 0.4783
WVFGRD96 67.0 20 65 20 4.51 0.4793
WVFGRD96 68.0 20 65 20 4.51 0.4794
WVFGRD96 69.0 20 65 20 4.52 0.4803
WVFGRD96 70.0 20 65 20 4.52 0.4808
WVFGRD96 71.0 20 65 20 4.52 0.4802
WVFGRD96 72.0 20 65 20 4.53 0.4810
WVFGRD96 73.0 20 65 20 4.53 0.4803
WVFGRD96 74.0 20 65 20 4.53 0.4801
WVFGRD96 75.0 20 65 20 4.54 0.4801
WVFGRD96 76.0 20 65 20 4.54 0.4785
WVFGRD96 77.0 20 65 20 4.54 0.4788
WVFGRD96 78.0 20 65 20 4.54 0.4776
WVFGRD96 79.0 20 65 20 4.55 0.4767
WVFGRD96 80.0 20 65 20 4.55 0.4756
WVFGRD96 81.0 20 65 20 4.55 0.4742
WVFGRD96 82.0 20 65 20 4.55 0.4734
WVFGRD96 83.0 20 65 20 4.56 0.4715
WVFGRD96 84.0 20 65 20 4.56 0.4707
WVFGRD96 85.0 20 65 20 4.56 0.4688
WVFGRD96 86.0 20 65 20 4.56 0.4674
WVFGRD96 87.0 20 65 20 4.56 0.4659
WVFGRD96 88.0 25 65 20 4.56 0.4642
WVFGRD96 89.0 25 65 20 4.57 0.4631
WVFGRD96 90.0 25 65 20 4.57 0.4615
WVFGRD96 91.0 25 65 20 4.57 0.4602
WVFGRD96 92.0 25 65 20 4.57 0.4586
WVFGRD96 93.0 25 65 20 4.57 0.4570
WVFGRD96 94.0 25 70 20 4.58 0.4555
WVFGRD96 95.0 25 70 20 4.58 0.4542
WVFGRD96 96.0 25 70 20 4.58 0.4530
WVFGRD96 97.0 25 70 20 4.58 0.4515
WVFGRD96 98.0 25 70 20 4.58 0.4503
WVFGRD96 99.0 25 70 20 4.59 0.4489
The best solution is
WVFGRD96 72.0 20 65 20 4.53 0.4810
The mechanism corresponding to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
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Figure 2. Depth sensitivity for waveform mechanism
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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 and because the velocity model used in the predictions may not be perfect.
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
hp c 0.02 n 3
lp c 0.06 n 3
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Figure 3. Waveform comparison for selected depth
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms.
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.
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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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Discussion
Acknowledgements
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
Velocity Model
The WUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Quality Control
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
Last Changed Mon Dec 7 00:25:31 CST 2015
