Location
Location ANSS
The ANSS event ID is ak012fftc799 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak012fftc799/executive.
2012/12/01 08:00:57 58.423 -154.118 84.7 5.4 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2012/12/01 08:00:57:0 58.42 -154.12 84.7 5.4 Alaska
Stations used:
AK.BRLK AK.CAST AK.CNP AK.EYAK AK.FID AK.HOM AK.KNK AK.PPLA
AK.PWL AK.RC01 AK.SAW AK.SCM AK.SII AK.SWD AT.CHGN AT.MID
AT.OHAK AT.PMR AT.SVW2
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.24e+24 dyne-cm
Mw = 5.33
Z = 92 km
Plane Strike Dip Rake
NP1 65 85 55
NP2 328 35 171
Principal Axes:
Axis Value Plunge Azimuth
T 1.24e+24 40 303
N 0.00e+00 35 68
P -1.24e+24 31 183
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.90e+23
Mxy -3.89e+23
Mxz 8.84e+23
Myy 5.13e+23
Myz -4.81e+23
Mzz 1.77e+23
--------------
########--------------
################------------
####################----------
########################----------
###########################---------
####### ####################-------#
######## T #####################---#####
######## #####################-#######
##############################-----#######
##########################---------#######
######################--------------######
##################------------------######
#############----------------------#####
########---------------------------#####
##--------------------------------####
---------------------------------###
--------------- -------------###
------------- P ------------##
------------ -----------##
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.77e+23 8.84e+23 4.81e+23
8.84e+23 -6.90e+23 3.89e+23
4.81e+23 3.89e+23 5.13e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121201080057/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 65
DIP = 85
RAKE = 55
MW = 5.33
HS = 92.0
The NDK file is 20121201080057.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
| SLU |
USGSMT |
USGS/SLU Moment Tensor Solution
ENS 2012/12/01 08:00:57:0 58.42 -154.12 84.7 5.4 Alaska
Stations used:
AK.BRLK AK.CAST AK.CNP AK.EYAK AK.FID AK.HOM AK.KNK AK.PPLA
AK.PWL AK.RC01 AK.SAW AK.SCM AK.SII AK.SWD AT.CHGN AT.MID
AT.OHAK AT.PMR AT.SVW2
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.24e+24 dyne-cm
Mw = 5.33
Z = 92 km
Plane Strike Dip Rake
NP1 65 85 55
NP2 328 35 171
Principal Axes:
Axis Value Plunge Azimuth
T 1.24e+24 40 303
N 0.00e+00 35 68
P -1.24e+24 31 183
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.90e+23
Mxy -3.89e+23
Mxz 8.84e+23
Myy 5.13e+23
Myz -4.81e+23
Mzz 1.77e+23
--------------
########--------------
################------------
####################----------
########################----------
###########################---------
####### ####################-------#
######## T #####################---#####
######## #####################-#######
##############################-----#######
##########################---------#######
######################--------------######
##################------------------######
#############----------------------#####
########---------------------------#####
##--------------------------------####
---------------------------------###
--------------- -------------###
------------- P ------------##
------------ -----------##
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.77e+23 8.84e+23 4.81e+23
8.84e+23 -6.90e+23 3.89e+23
4.81e+23 3.89e+23 5.13e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121201080057/index.html
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USGS WPhase Moment Solution
ALASKA PENINSULA
12/12/01 8:00:57
Epicenter: 58.533 -154.180
MW 5.3
USGS/WPHASE CENTROID MOMENT TENSOR
12/12/01 08:00:57.00
Centroid: 58.433 -153.796
Depth 100 No. of sta: 35
Moment Tensor; Scale 10**16 Nm
Mrr= 4.21 Mtt=-9.92
Mpp= 5.70 Mrt= 6.42
Mrp= 4.37 Mtp= 0.09
Principal axes:
T Val= 10.38 Plg=45 Azm=288
N = 2.15 36 67
P =-12.53 22 174
Best Double Couple:Mo=1.2*10**17
NP1:Strike=310 Dip=40 Slip= 158
NP2: 57 76 52
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Magnitudes
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.
ML Magnitude
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.
Context
The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. 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). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.
Waveform Inversion using wvfgrd96
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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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'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:
hp c 0.02 n 3
lp c 0.05 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 50 45 -65 4.50 0.1438
WVFGRD96 1.0 40 45 -80 4.54 0.1550
WVFGRD96 2.0 45 45 -75 4.61 0.1859
WVFGRD96 3.0 40 40 -85 4.67 0.2048
WVFGRD96 4.0 220 50 -90 4.71 0.2087
WVFGRD96 5.0 120 45 -60 4.64 0.2025
WVFGRD96 6.0 120 45 -55 4.66 0.2031
WVFGRD96 7.0 120 45 -55 4.67 0.1984
WVFGRD96 8.0 120 45 -55 4.70 0.2084
WVFGRD96 9.0 130 50 -45 4.68 0.1993
WVFGRD96 10.0 135 50 -30 4.67 0.1952
WVFGRD96 11.0 135 50 -25 4.67 0.1909
WVFGRD96 12.0 135 50 -25 4.67 0.1893
WVFGRD96 13.0 140 55 -20 4.67 0.1886
WVFGRD96 14.0 140 55 -15 4.67 0.1862
WVFGRD96 15.0 140 55 -15 4.68 0.1866
WVFGRD96 16.0 140 55 -15 4.68 0.1845
WVFGRD96 17.0 150 45 15 4.70 0.1876
WVFGRD96 18.0 150 45 15 4.71 0.1910
WVFGRD96 19.0 150 45 15 4.72 0.1916
WVFGRD96 20.0 150 45 15 4.73 0.1949
WVFGRD96 21.0 70 90 40 4.72 0.1963
WVFGRD96 22.0 70 90 40 4.74 0.2006
WVFGRD96 23.0 70 90 40 4.75 0.2048
WVFGRD96 24.0 250 85 -40 4.76 0.2100
WVFGRD96 25.0 70 90 40 4.77 0.2139
WVFGRD96 26.0 70 90 40 4.78 0.2185
WVFGRD96 27.0 250 85 -40 4.79 0.2250
WVFGRD96 28.0 245 80 -45 4.81 0.2303
WVFGRD96 29.0 245 80 -45 4.82 0.2359
WVFGRD96 30.0 245 80 -45 4.83 0.2416
WVFGRD96 31.0 245 80 -45 4.84 0.2471
WVFGRD96 32.0 245 80 -45 4.85 0.2526
WVFGRD96 33.0 245 80 -45 4.86 0.2581
WVFGRD96 34.0 250 80 -40 4.87 0.2640
WVFGRD96 35.0 250 80 -40 4.89 0.2699
WVFGRD96 36.0 250 80 -35 4.90 0.2755
WVFGRD96 37.0 250 85 -35 4.91 0.2816
WVFGRD96 38.0 250 85 -35 4.93 0.2875
WVFGRD96 39.0 250 85 -30 4.95 0.2935
WVFGRD96 40.0 245 70 -50 5.04 0.3109
WVFGRD96 41.0 245 70 -50 5.05 0.3168
WVFGRD96 42.0 240 70 -50 5.06 0.3230
WVFGRD96 43.0 240 70 -50 5.07 0.3292
WVFGRD96 44.0 240 70 -50 5.08 0.3352
WVFGRD96 45.0 240 70 -50 5.09 0.3412
WVFGRD96 46.0 240 70 -50 5.10 0.3472
WVFGRD96 47.0 240 70 -50 5.11 0.3530
WVFGRD96 48.0 240 70 -50 5.12 0.3587
WVFGRD96 49.0 240 75 -50 5.13 0.3646
WVFGRD96 50.0 240 75 -50 5.14 0.3710
WVFGRD96 51.0 240 75 -45 5.15 0.3786
WVFGRD96 52.0 240 75 -45 5.15 0.3858
WVFGRD96 53.0 245 80 -45 5.16 0.3931
WVFGRD96 54.0 245 80 -45 5.17 0.4002
WVFGRD96 55.0 245 80 -45 5.18 0.4071
WVFGRD96 56.0 245 80 -45 5.18 0.4138
WVFGRD96 57.0 245 80 -45 5.19 0.4204
WVFGRD96 58.0 245 80 -45 5.20 0.4266
WVFGRD96 59.0 245 85 -45 5.21 0.4332
WVFGRD96 60.0 245 85 -45 5.21 0.4396
WVFGRD96 61.0 245 85 -45 5.22 0.4456
WVFGRD96 62.0 245 85 -45 5.23 0.4513
WVFGRD96 63.0 245 85 -45 5.23 0.4566
WVFGRD96 64.0 245 85 -45 5.24 0.4617
WVFGRD96 65.0 245 85 -45 5.24 0.4664
WVFGRD96 66.0 245 85 -45 5.25 0.4707
WVFGRD96 67.0 245 85 -45 5.25 0.4748
WVFGRD96 68.0 245 85 -45 5.26 0.4787
WVFGRD96 69.0 245 85 -45 5.26 0.4823
WVFGRD96 70.0 245 85 -45 5.27 0.4855
WVFGRD96 71.0 245 85 -45 5.27 0.4884
WVFGRD96 72.0 245 85 -45 5.27 0.4918
WVFGRD96 73.0 240 85 -50 5.29 0.4952
WVFGRD96 74.0 65 90 50 5.28 0.4989
WVFGRD96 75.0 245 90 -50 5.29 0.5034
WVFGRD96 76.0 65 90 50 5.29 0.5075
WVFGRD96 77.0 65 90 50 5.29 0.5112
WVFGRD96 78.0 65 90 50 5.30 0.5144
WVFGRD96 79.0 65 90 50 5.30 0.5173
WVFGRD96 80.0 65 90 50 5.30 0.5200
WVFGRD96 81.0 65 90 50 5.31 0.5225
WVFGRD96 82.0 245 90 -50 5.31 0.5246
WVFGRD96 83.0 65 90 50 5.31 0.5260
WVFGRD96 84.0 65 90 50 5.31 0.5274
WVFGRD96 85.0 245 90 -50 5.31 0.5285
WVFGRD96 86.0 65 90 50 5.32 0.5291
WVFGRD96 87.0 245 90 -50 5.32 0.5296
WVFGRD96 88.0 65 90 55 5.32 0.5304
WVFGRD96 89.0 245 90 -55 5.33 0.5308
WVFGRD96 90.0 245 90 -55 5.33 0.5307
WVFGRD96 91.0 65 85 55 5.32 0.5312
WVFGRD96 92.0 65 85 55 5.33 0.5312
WVFGRD96 93.0 245 90 -55 5.33 0.5299
WVFGRD96 94.0 65 85 55 5.33 0.5301
WVFGRD96 95.0 245 90 -55 5.33 0.5278
WVFGRD96 96.0 65 85 55 5.33 0.5284
WVFGRD96 97.0 65 85 55 5.33 0.5270
WVFGRD96 98.0 65 85 55 5.33 0.5255
WVFGRD96 99.0 65 85 55 5.33 0.5240
WVFGRD96 100.0 65 85 55 5.33 0.5223
WVFGRD96 101.0 65 85 55 5.33 0.5203
WVFGRD96 102.0 245 90 -55 5.34 0.5148
WVFGRD96 103.0 245 90 -55 5.34 0.5125
WVFGRD96 104.0 240 90 -60 5.35 0.5103
WVFGRD96 105.0 240 90 -60 5.35 0.5075
WVFGRD96 106.0 65 85 60 5.34 0.5097
WVFGRD96 107.0 65 85 60 5.34 0.5073
WVFGRD96 108.0 65 85 60 5.34 0.5046
WVFGRD96 109.0 65 85 60 5.34 0.5020
WVFGRD96 110.0 65 85 60 5.34 0.4993
WVFGRD96 111.0 65 85 60 5.34 0.4963
WVFGRD96 112.0 65 85 60 5.34 0.4933
WVFGRD96 113.0 65 85 60 5.34 0.4904
WVFGRD96 114.0 65 85 60 5.34 0.4872
WVFGRD96 115.0 65 85 60 5.34 0.4841
WVFGRD96 116.0 65 85 60 5.34 0.4808
WVFGRD96 117.0 65 85 60 5.34 0.4775
WVFGRD96 118.0 65 85 60 5.34 0.4740
WVFGRD96 119.0 65 85 60 5.34 0.4707
WVFGRD96 120.0 65 85 60 5.34 0.4673
WVFGRD96 121.0 70 80 55 5.32 0.4638
WVFGRD96 122.0 70 80 55 5.32 0.4607
WVFGRD96 123.0 70 80 55 5.32 0.4573
WVFGRD96 124.0 70 80 55 5.32 0.4542
WVFGRD96 125.0 70 80 55 5.32 0.4508
WVFGRD96 126.0 70 80 55 5.32 0.4477
WVFGRD96 127.0 65 80 60 5.33 0.4443
WVFGRD96 128.0 65 80 60 5.33 0.4413
WVFGRD96 129.0 65 80 60 5.33 0.4380
The best solution is
WVFGRD96 92.0 65 85 55 5.33 0.5312
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, 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
hp c 0.02 n 3
lp c 0.05 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.
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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.
Velocity Model
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
Last Changed Sat Apr 27 12:16:18 AM CDT 2024
