Location
Location ANSS
The ANSS event ID is ak014fasfc4y and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak014fasfc4y/executive.
2014/11/29 04:14:16 62.724 -150.485 97.1 5.1 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/11/29 04:14:16:0 62.72 -150.49 97.1 5.1 Alaska
Stations used:
AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.DHY AK.DOT
AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT AK.ISLE AK.KLU
AK.KNK AK.KTH AK.MCAR AK.MDM AK.MESA AK.PAX AK.PPLA AK.RAG
AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.SWD AK.TABL
AK.TGL AK.TRF AK.WRH AK.YAH AT.TTA IM.IL31 IU.COLA TA.I23K
TA.K27K TA.M24K TA.N25K TA.O22K TA.POKR
Filtering commands used:
cut o DIST/3.3 -50 o DIST/3.3 +70
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 = 106 km
Plane Strike Dip Rake
NP1 352 66 141
NP2 100 55 30
Principal Axes:
Axis Value Plunge Azimuth
T 3.35e+23 44 312
N 0.00e+00 45 145
P -3.35e+23 7 48
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.14e+22
Mxy -2.50e+23
Mxz 8.53e+22
Myy -8.60e+22
Myz -1.54e+23
Mzz 1.57e+23
#####---------
###########-----------
###############-------------
#################------------
####################----------- P
######## ###########---------- -
######### T ###########---------------
########## ############---------------
#########################---------------
-##########################---------------
--#########################---------------
----#######################---------------
------#####################---------------
-------####################------------#
-----------################---------####
----------------##########-----#######
------------------------############
-----------------------###########
---------------------#########
-------------------#########
----------------######
-----------###
Global CMT Convention Moment Tensor:
R T P
1.57e+23 8.53e+22 1.54e+23
8.53e+22 -7.14e+22 2.50e+23
1.54e+23 2.50e+23 -8.60e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141129041416/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 100
DIP = 55
RAKE = 30
MW = 4.95
HS = 106.0
The NDK file is 20141129041416.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 2014/11/29 04:14:16:0 62.72 -150.49 97.1 5.1 Alaska
Stations used:
AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.DHY AK.DOT
AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT AK.ISLE AK.KLU
AK.KNK AK.KTH AK.MCAR AK.MDM AK.MESA AK.PAX AK.PPLA AK.RAG
AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.SWD AK.TABL
AK.TGL AK.TRF AK.WRH AK.YAH AT.TTA IM.IL31 IU.COLA TA.I23K
TA.K27K TA.M24K TA.N25K TA.O22K TA.POKR
Filtering commands used:
cut o DIST/3.3 -50 o DIST/3.3 +70
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 = 106 km
Plane Strike Dip Rake
NP1 352 66 141
NP2 100 55 30
Principal Axes:
Axis Value Plunge Azimuth
T 3.35e+23 44 312
N 0.00e+00 45 145
P -3.35e+23 7 48
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.14e+22
Mxy -2.50e+23
Mxz 8.53e+22
Myy -8.60e+22
Myz -1.54e+23
Mzz 1.57e+23
#####---------
###########-----------
###############-------------
#################------------
####################----------- P
######## ###########---------- -
######### T ###########---------------
########## ############---------------
#########################---------------
-##########################---------------
--#########################---------------
----#######################---------------
------#####################---------------
-------####################------------#
-----------################---------####
----------------##########-----#######
------------------------############
-----------------------###########
---------------------#########
-------------------#########
----------------######
-----------###
Global CMT Convention Moment Tensor:
R T P
1.57e+23 8.53e+22 1.54e+23
8.53e+22 -7.14e+22 2.50e+23
1.54e+23 2.50e+23 -8.60e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141129041416/index.html
|
Moment 3.34e+16 N-m
Magnitude 4.9
Percent DC 81%
Depth 99.0 km
Updated 2014-11-29 05:28:59 UTC
Author us
Catalog us
Contributor Code us_b000t12u_mwr
Principal Axes
Axis Value Plunge Azimuth
T 3.492 47 310
N -0.320 42 146
P -3.173 8 48
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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:
cut o DIST/3.3 -50 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 145 45 -95 4.16 0.2667
WVFGRD96 4.0 170 45 -55 4.21 0.2358
WVFGRD96 6.0 5 45 -20 4.20 0.2498
WVFGRD96 8.0 5 45 -20 4.26 0.2704
WVFGRD96 10.0 10 50 -10 4.27 0.2815
WVFGRD96 12.0 10 50 -5 4.28 0.2905
WVFGRD96 14.0 15 50 10 4.30 0.2974
WVFGRD96 16.0 15 55 10 4.32 0.3021
WVFGRD96 18.0 300 60 45 4.34 0.3066
WVFGRD96 20.0 300 60 45 4.35 0.3127
WVFGRD96 22.0 295 60 40 4.38 0.3169
WVFGRD96 24.0 110 85 35 4.40 0.3209
WVFGRD96 26.0 110 80 35 4.42 0.3248
WVFGRD96 28.0 110 80 35 4.43 0.3281
WVFGRD96 30.0 105 85 30 4.46 0.3302
WVFGRD96 32.0 105 90 30 4.48 0.3332
WVFGRD96 34.0 105 90 30 4.49 0.3351
WVFGRD96 36.0 105 90 30 4.51 0.3354
WVFGRD96 38.0 285 85 -25 4.55 0.3388
WVFGRD96 40.0 285 90 -35 4.62 0.3407
WVFGRD96 42.0 285 85 -35 4.63 0.3415
WVFGRD96 44.0 285 90 -30 4.65 0.3418
WVFGRD96 46.0 105 90 30 4.66 0.3421
WVFGRD96 48.0 105 80 30 4.68 0.3440
WVFGRD96 50.0 100 65 -15 4.71 0.3505
WVFGRD96 52.0 100 65 -15 4.72 0.3585
WVFGRD96 54.0 100 65 -15 4.74 0.3660
WVFGRD96 56.0 100 45 25 4.77 0.3881
WVFGRD96 58.0 100 45 25 4.79 0.4074
WVFGRD96 60.0 100 50 30 4.80 0.4294
WVFGRD96 62.0 100 50 30 4.82 0.4544
WVFGRD96 64.0 100 50 30 4.83 0.4812
WVFGRD96 66.0 100 50 30 4.85 0.5080
WVFGRD96 68.0 105 45 35 4.86 0.5341
WVFGRD96 70.0 100 50 30 4.87 0.5591
WVFGRD96 72.0 100 50 30 4.88 0.5853
WVFGRD96 74.0 100 50 30 4.89 0.6113
WVFGRD96 76.0 105 50 35 4.90 0.6354
WVFGRD96 78.0 105 50 35 4.91 0.6589
WVFGRD96 80.0 105 50 35 4.91 0.6797
WVFGRD96 82.0 105 50 35 4.92 0.6986
WVFGRD96 84.0 105 50 35 4.93 0.7149
WVFGRD96 86.0 105 50 35 4.93 0.7288
WVFGRD96 88.0 105 50 35 4.93 0.7408
WVFGRD96 90.0 105 50 35 4.93 0.7501
WVFGRD96 92.0 105 50 35 4.94 0.7577
WVFGRD96 94.0 105 50 35 4.94 0.7636
WVFGRD96 96.0 105 50 35 4.94 0.7676
WVFGRD96 98.0 105 50 35 4.94 0.7705
WVFGRD96 100.0 105 50 35 4.94 0.7720
WVFGRD96 102.0 105 50 35 4.94 0.7726
WVFGRD96 104.0 100 55 30 4.95 0.7728
WVFGRD96 106.0 100 55 30 4.95 0.7733
WVFGRD96 108.0 100 55 30 4.95 0.7731
WVFGRD96 110.0 100 55 30 4.95 0.7719
WVFGRD96 112.0 100 55 30 4.95 0.7698
WVFGRD96 114.0 100 55 30 4.95 0.7672
WVFGRD96 116.0 100 55 30 4.95 0.7642
WVFGRD96 118.0 100 55 30 4.95 0.7611
The best solution is
WVFGRD96 106.0 100 55 30 4.95 0.7733
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
cut o DIST/3.3 -50 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 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 03:41:23 AM CDT 2024
