Location
Location ANSS
The ANSS event ID is ak012fko16th and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak012fko16th/executive.
2012/12/04 01:42:48 61.240 -150.768 63.7 5.8 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2012/12/04 01:42:48:0 61.24 -150.77 63.7 5.8 Alaska
Stations used:
AK.BMR AK.BPAW AK.BRLK AK.CAST AK.CCB AK.CNP AK.DHY AK.DIV
AK.DOT AK.EYAK AK.FID AK.GHO AK.GLI AK.GLM AK.HMT AK.HOM
AK.KLU AK.KNK AK.MCK AK.MDM AK.PAX AK.PIN AK.PPD AK.PPLA
AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.SKN AK.SWD AK.TRF
AT.MID AT.PMR AT.SVW2 IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 4.47e+24 dyne-cm
Mw = 5.70
Z = 63 km
Plane Strike Dip Rake
NP1 320 70 142
NP2 65 55 25
Principal Axes:
Axis Value Plunge Azimuth
T 4.47e+24 41 277
N 0.00e+00 48 116
P -4.47e+24 9 15
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.00e+24
Mxy -1.45e+24
Mxz -3.96e+23
Myy 2.22e+24
Myz -2.38e+24
Mzz 1.77e+24
-----------
--------------- P ----
#----------------- -------
#######-----------------------
############----------------------
###############---------------------
##################--------------------
#####################-----------------##
#######################--------------###
####### ###############------------#####
####### T #################---------######
####### ##################-------#######
#############################----#########
########################################
###########################---##########
######################--------########
--##############--------------######
------------------------------####
----------------------------##
---------------------------#
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.77e+24 -3.96e+23 2.38e+24
-3.96e+23 -4.00e+24 1.45e+24
2.38e+24 1.45e+24 2.22e+24
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121204014248/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 = 55
RAKE = 25
MW = 5.70
HS = 63.0
The NDK file is 20121204014248.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 |
GCMT |
USGSCMT |
USGS/SLU Moment Tensor Solution
ENS 2012/12/04 01:42:48:0 61.24 -150.77 63.7 5.8 Alaska
Stations used:
AK.BMR AK.BPAW AK.BRLK AK.CAST AK.CCB AK.CNP AK.DHY AK.DIV
AK.DOT AK.EYAK AK.FID AK.GHO AK.GLI AK.GLM AK.HMT AK.HOM
AK.KLU AK.KNK AK.MCK AK.MDM AK.PAX AK.PIN AK.PPD AK.PPLA
AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.SKN AK.SWD AK.TRF
AT.MID AT.PMR AT.SVW2 IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 4.47e+24 dyne-cm
Mw = 5.70
Z = 63 km
Plane Strike Dip Rake
NP1 320 70 142
NP2 65 55 25
Principal Axes:
Axis Value Plunge Azimuth
T 4.47e+24 41 277
N 0.00e+00 48 116
P -4.47e+24 9 15
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.00e+24
Mxy -1.45e+24
Mxz -3.96e+23
Myy 2.22e+24
Myz -2.38e+24
Mzz 1.77e+24
-----------
--------------- P ----
#----------------- -------
#######-----------------------
############----------------------
###############---------------------
##################--------------------
#####################-----------------##
#######################--------------###
####### ###############------------#####
####### T #################---------######
####### ##################-------#######
#############################----#########
########################################
###########################---##########
######################--------########
--##############--------------######
------------------------------####
----------------------------##
---------------------------#
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.77e+24 -3.96e+23 2.38e+24
-3.96e+23 -4.00e+24 1.45e+24
2.38e+24 1.45e+24 2.22e+24
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121204014248/index.html
|
USGS Body-Wave Moment Tensor Solution
12/12/04 01:42:48.00
Epicenter: 61.230 -150.719
MW 5.7
USGS MOMENT TENSOR SOLUTION
Depth 60 No. of sta: 35
Moment Tensor; Scale 10**17 Nm
Mrr= 2.34 Mtt=-4.28
Mpp= 1.95 Mrt= 0.08
Mrp= 3.22 Mtp= 1.86
Principal axes:
T Val= 5.55 Plg=45 Azm=281
N -0.65 44 116
P -4.90 7 19
Best Double Couple:Mo=5.3*10**17
NP1:Strike=322 Dip=66 Slip= 140
NP2: 70 54 30
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December 4, 2012, SOUTHERN ALASKA, MW=5.8
Howard Koss
CENTROID-MOMENT-TENSOR SOLUTION
GCMT EVENT: C201212040142A
DATA: II IU CU MN G IC LD GE DK
L.P.BODY WAVES:132S, 271C, T= 40
MANTLE WAVES: 56S, 61C, T=125
SURFACE WAVES: 139S, 287C, T= 50
TIMESTAMP: Q-20121204101317
CENTROID LOCATION:
ORIGIN TIME: 01:42:51.6 0.1
LAT:61.43N 0.01;LON:150.89W 0.01
DEP: 67.6 0.8;TRIANG HDUR: 1.9
MOMENT TENSOR: SCALE 10**24 D-CM
RR= 1.270 0.047; TT=-3.710 0.050
PP= 2.440 0.051; RT= 0.390 0.044
RP= 3.390 0.042; TP= 2.920 0.046
PRINCIPAL AXES:
1.(T) VAL= 5.956;PLG=35;AZM=288
2.(N) -0.922; 53; 129
3.(P) -5.034; 10; 26
BEST DBLE.COUPLE:M0= 5.50*10**24
NP1: STRIKE= 73;DIP=58;SLIP= 20
NP2: STRIKE=332;DIP=73;SLIP= 146
----------
###----------- P --
#######--------- ----
###########----------------
#############----------------
################---------------
#### ##########--------------
##### T ###########------------##
##### ############----------###
#####################-------#####
######################----#######
#####################-#########
---##############-----#########
---------------------########
---------------------######
-------------------####
-----------------##
-----------
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USGS WPhase Moment Solution
12/12/04 1:42:48
Epicenter: 61.230 -150.719
MW 5.8
USGS/WPHASE CENTROID MOMENT TENSOR
12/12/04 01:42:48.00
Centroid: 61.230 -150.719
Depth 50 No. of sta: 36
Moment Tensor; Scale 10**17 Nm
Mrr= 2.41 Mtt=-3.82
Mpp= 1.42 Mrt= 0.22
Mrp= 3.55 Mtp= 2.38
Principal axes:
T Val= 5.82 Plg=45 Azm=285
N = -0.88 42 125
P = -4.94 10 26
Best Double Couple:Mo=5.4*10**17
NP1:Strike= 77 Dip=51 Slip= 29
NP2: 328 68 137
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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 1.0 210 50 -75 4.97 0.2202
WVFGRD96 2.0 220 60 -45 5.05 0.2827
WVFGRD96 3.0 205 50 -70 5.13 0.3112
WVFGRD96 4.0 225 80 -25 5.10 0.3220
WVFGRD96 5.0 230 90 -15 5.11 0.3377
WVFGRD96 6.0 50 85 15 5.14 0.3551
WVFGRD96 7.0 50 80 10 5.16 0.3721
WVFGRD96 8.0 50 75 10 5.19 0.3887
WVFGRD96 9.0 50 75 10 5.21 0.4020
WVFGRD96 10.0 50 75 10 5.22 0.4134
WVFGRD96 11.0 50 75 10 5.24 0.4229
WVFGRD96 12.0 50 75 10 5.25 0.4309
WVFGRD96 13.0 55 70 10 5.25 0.4391
WVFGRD96 14.0 55 70 10 5.26 0.4482
WVFGRD96 15.0 55 70 15 5.27 0.4598
WVFGRD96 16.0 55 70 15 5.28 0.4725
WVFGRD96 17.0 55 70 15 5.29 0.4851
WVFGRD96 18.0 55 70 15 5.30 0.4973
WVFGRD96 19.0 55 70 15 5.31 0.5091
WVFGRD96 20.0 55 70 15 5.32 0.5205
WVFGRD96 21.0 55 70 15 5.33 0.5310
WVFGRD96 22.0 55 70 15 5.34 0.5417
WVFGRD96 23.0 55 70 15 5.34 0.5520
WVFGRD96 24.0 55 70 15 5.35 0.5619
WVFGRD96 25.0 55 70 15 5.36 0.5714
WVFGRD96 26.0 55 70 10 5.37 0.5808
WVFGRD96 27.0 55 70 10 5.38 0.5898
WVFGRD96 28.0 55 70 10 5.39 0.5985
WVFGRD96 29.0 60 65 15 5.39 0.6074
WVFGRD96 30.0 60 65 15 5.40 0.6160
WVFGRD96 31.0 60 65 15 5.41 0.6245
WVFGRD96 32.0 60 65 15 5.42 0.6326
WVFGRD96 33.0 60 65 15 5.43 0.6404
WVFGRD96 34.0 60 65 15 5.44 0.6482
WVFGRD96 35.0 60 65 15 5.45 0.6557
WVFGRD96 36.0 60 65 15 5.46 0.6633
WVFGRD96 37.0 60 65 15 5.47 0.6707
WVFGRD96 38.0 60 65 15 5.48 0.6780
WVFGRD96 39.0 60 65 10 5.49 0.6847
WVFGRD96 40.0 60 55 15 5.56 0.6904
WVFGRD96 41.0 60 55 15 5.57 0.6976
WVFGRD96 42.0 60 55 15 5.57 0.7043
WVFGRD96 43.0 60 60 20 5.58 0.7109
WVFGRD96 44.0 60 60 20 5.59 0.7173
WVFGRD96 45.0 60 60 20 5.60 0.7233
WVFGRD96 46.0 60 60 20 5.61 0.7292
WVFGRD96 47.0 60 60 20 5.61 0.7348
WVFGRD96 48.0 60 60 20 5.62 0.7403
WVFGRD96 49.0 60 60 20 5.63 0.7455
WVFGRD96 50.0 65 55 20 5.63 0.7503
WVFGRD96 51.0 65 55 20 5.64 0.7550
WVFGRD96 52.0 65 55 25 5.64 0.7593
WVFGRD96 53.0 65 55 25 5.65 0.7631
WVFGRD96 54.0 65 55 25 5.65 0.7667
WVFGRD96 55.0 65 55 25 5.66 0.7698
WVFGRD96 56.0 65 55 25 5.67 0.7726
WVFGRD96 57.0 65 55 25 5.67 0.7750
WVFGRD96 58.0 65 55 25 5.68 0.7769
WVFGRD96 59.0 65 55 25 5.68 0.7784
WVFGRD96 60.0 65 55 25 5.69 0.7796
WVFGRD96 61.0 65 55 25 5.69 0.7804
WVFGRD96 62.0 65 55 25 5.69 0.7805
WVFGRD96 63.0 65 55 25 5.70 0.7805
WVFGRD96 64.0 65 55 25 5.70 0.7804
WVFGRD96 65.0 65 55 25 5.71 0.7793
WVFGRD96 66.0 65 55 25 5.71 0.7783
WVFGRD96 67.0 65 55 25 5.71 0.7771
WVFGRD96 68.0 65 55 25 5.72 0.7753
WVFGRD96 69.0 65 55 25 5.72 0.7734
WVFGRD96 70.0 65 55 25 5.72 0.7709
WVFGRD96 71.0 65 55 25 5.73 0.7683
WVFGRD96 72.0 65 55 25 5.73 0.7661
WVFGRD96 73.0 65 55 25 5.73 0.7632
WVFGRD96 74.0 65 55 25 5.73 0.7602
WVFGRD96 75.0 65 55 25 5.74 0.7574
WVFGRD96 76.0 65 55 25 5.74 0.7540
WVFGRD96 77.0 65 55 25 5.74 0.7507
WVFGRD96 78.0 65 55 25 5.74 0.7469
WVFGRD96 79.0 65 55 25 5.75 0.7432
WVFGRD96 80.0 65 55 25 5.75 0.7391
WVFGRD96 81.0 65 55 25 5.75 0.7352
WVFGRD96 82.0 65 55 25 5.75 0.7305
WVFGRD96 83.0 65 55 25 5.75 0.7264
WVFGRD96 84.0 65 55 25 5.76 0.7220
WVFGRD96 85.0 65 55 25 5.76 0.7172
WVFGRD96 86.0 65 55 25 5.76 0.7126
WVFGRD96 87.0 70 55 25 5.76 0.7081
WVFGRD96 88.0 70 55 25 5.76 0.7036
WVFGRD96 89.0 70 55 25 5.76 0.6988
WVFGRD96 90.0 70 55 25 5.76 0.6946
WVFGRD96 91.0 70 55 25 5.76 0.6900
WVFGRD96 92.0 70 55 25 5.76 0.6852
WVFGRD96 93.0 70 55 25 5.76 0.6806
WVFGRD96 94.0 70 55 25 5.76 0.6756
WVFGRD96 95.0 70 55 25 5.77 0.6712
WVFGRD96 96.0 70 55 25 5.77 0.6664
WVFGRD96 97.0 70 55 25 5.77 0.6617
WVFGRD96 98.0 70 55 25 5.77 0.6569
WVFGRD96 99.0 70 55 25 5.77 0.6527
WVFGRD96 100.0 70 55 25 5.77 0.6479
WVFGRD96 101.0 70 55 25 5.77 0.6437
WVFGRD96 102.0 70 55 25 5.77 0.6392
WVFGRD96 103.0 70 55 25 5.77 0.6349
WVFGRD96 104.0 70 55 25 5.78 0.6307
WVFGRD96 105.0 70 55 25 5.78 0.6261
WVFGRD96 106.0 70 55 20 5.78 0.6224
WVFGRD96 107.0 70 55 20 5.78 0.6182
WVFGRD96 108.0 70 55 20 5.78 0.6147
WVFGRD96 109.0 70 55 20 5.78 0.6107
WVFGRD96 110.0 70 55 20 5.78 0.6068
WVFGRD96 111.0 70 55 20 5.79 0.6031
WVFGRD96 112.0 70 55 20 5.79 0.5991
WVFGRD96 113.0 70 55 20 5.79 0.5957
WVFGRD96 114.0 70 55 20 5.79 0.5920
WVFGRD96 115.0 70 55 20 5.79 0.5884
WVFGRD96 116.0 65 60 20 5.79 0.5849
WVFGRD96 117.0 65 60 20 5.79 0.5813
WVFGRD96 118.0 65 60 20 5.79 0.5782
WVFGRD96 119.0 65 60 20 5.79 0.5747
WVFGRD96 120.0 65 60 20 5.80 0.5714
WVFGRD96 121.0 65 60 20 5.80 0.5682
WVFGRD96 122.0 65 60 20 5.80 0.5653
WVFGRD96 123.0 65 60 20 5.80 0.5621
WVFGRD96 124.0 65 60 20 5.80 0.5594
WVFGRD96 125.0 65 60 20 5.80 0.5565
WVFGRD96 126.0 65 60 20 5.80 0.5534
WVFGRD96 127.0 65 60 20 5.80 0.5509
WVFGRD96 128.0 65 60 20 5.80 0.5479
WVFGRD96 129.0 65 60 20 5.80 0.5449
The best solution is
WVFGRD96 63.0 65 55 25 5.70 0.7805
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 12:40:46 AM CDT 2024
