Location
Location ANSS
The ANSS event ID is ak0147utj430 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak0147utj430/executive.
2014/06/20 01:06:22 63.133 -149.311 82.1 4.2 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/06/20 01:06:22:0 63.13 -149.31 82.1 4.2 Alaska
Stations used:
AK.BPAW AK.BRLK AK.CCB AK.CNP AK.CRQ AK.DHY AK.FID AK.FYU
AK.GHO AK.HIN AK.MCAR AK.MCK AK.PAX AK.RAG AK.RC01 AK.RIDG
AK.RND AK.SAW AK.SCM AK.TRF AK.VRDI AK.WRH AT.PMR 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 0.05 n 3
Best Fitting Double Couple
Mo = 2.79e+22 dyne-cm
Mw = 4.23
Z = 86 km
Plane Strike Dip Rake
NP1 110 75 25
NP2 13 66 164
Principal Axes:
Axis Value Plunge Azimuth
T 2.79e+22 28 333
N 0.00e+00 61 139
P -2.79e+22 6 240
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+22
Mxy -2.06e+22
Mxz 1.18e+22
Myy -1.64e+22
Myz -2.65e+21
Mzz 5.89e+21
############--
#################-----
###### ###########--------
####### T ############--------
######### ############----------
#########################-----------
##########################------------
-##########################-------------
---########################-------------
-------#####################--------------
----------#################---------------
-------------##############---------------
------------------#########---------------
----------------------###---------------
------------------------#####-----------
- -------------------###############
P ------------------###############
-----------------###############
----------------##############
--------------##############
---------#############
---###########
Global CMT Convention Moment Tensor:
R T P
5.89e+21 1.18e+22 2.65e+21
1.18e+22 1.05e+22 2.06e+22
2.65e+21 2.06e+22 -1.64e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140620010622/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 = 110
DIP = 75
RAKE = 25
MW = 4.23
HS = 86.0
The NDK file is 20140620010622.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 2014/06/20 01:06:22:0 63.13 -149.31 82.1 4.2 Alaska
Stations used:
AK.BPAW AK.BRLK AK.CCB AK.CNP AK.CRQ AK.DHY AK.FID AK.FYU
AK.GHO AK.HIN AK.MCAR AK.MCK AK.PAX AK.RAG AK.RC01 AK.RIDG
AK.RND AK.SAW AK.SCM AK.TRF AK.VRDI AK.WRH AT.PMR 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 0.05 n 3
Best Fitting Double Couple
Mo = 2.79e+22 dyne-cm
Mw = 4.23
Z = 86 km
Plane Strike Dip Rake
NP1 110 75 25
NP2 13 66 164
Principal Axes:
Axis Value Plunge Azimuth
T 2.79e+22 28 333
N 0.00e+00 61 139
P -2.79e+22 6 240
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+22
Mxy -2.06e+22
Mxz 1.18e+22
Myy -1.64e+22
Myz -2.65e+21
Mzz 5.89e+21
############--
#################-----
###### ###########--------
####### T ############--------
######### ############----------
#########################-----------
##########################------------
-##########################-------------
---########################-------------
-------#####################--------------
----------#################---------------
-------------##############---------------
------------------#########---------------
----------------------###---------------
------------------------#####-----------
- -------------------###############
P ------------------###############
-----------------###############
----------------##############
--------------##############
---------#############
---###########
Global CMT Convention Moment Tensor:
R T P
5.89e+21 1.18e+22 2.65e+21
1.18e+22 1.05e+22 2.06e+22
2.65e+21 2.06e+22 -1.64e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140620010622/index.html
|
Moment
2.92e+15 N-m
Magnitude
4.2
Percent DC
82%
Depth
86.0 km
Updated
2014-06-20 01:50:47 UTC
Author
us
Catalog
us
Contributor
us
Code
us_c000rii9_mwr
Principal Axes
Axis Value Plunge Azimuth
T 3.040 28 336
N -0.259 61 136
P -2.781 8 242
Nodal Planes
Plane Strike Dip Rake
NP1 112° 77 26
NP2 16° 65 166
|
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 a -30 a 180
rtr
taper w 0.1
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 2.0 195 65 -20 3.47 0.1995
WVFGRD96 4.0 260 80 -5 3.51 0.2430
WVFGRD96 6.0 260 85 0 3.56 0.2711
WVFGRD96 8.0 85 75 5 3.61 0.2955
WVFGRD96 10.0 85 75 -5 3.65 0.3131
WVFGRD96 12.0 85 75 -5 3.68 0.3254
WVFGRD96 14.0 90 75 5 3.69 0.3359
WVFGRD96 16.0 90 75 5 3.71 0.3481
WVFGRD96 18.0 90 75 5 3.73 0.3581
WVFGRD96 20.0 90 75 5 3.75 0.3668
WVFGRD96 22.0 95 75 5 3.77 0.3760
WVFGRD96 24.0 95 75 10 3.78 0.3849
WVFGRD96 26.0 95 75 10 3.80 0.3933
WVFGRD96 28.0 95 75 10 3.82 0.4011
WVFGRD96 30.0 100 75 10 3.84 0.4082
WVFGRD96 32.0 100 75 10 3.86 0.4150
WVFGRD96 34.0 105 75 15 3.88 0.4219
WVFGRD96 36.0 105 75 15 3.91 0.4278
WVFGRD96 38.0 105 75 10 3.94 0.4347
WVFGRD96 40.0 105 65 20 4.00 0.4556
WVFGRD96 42.0 105 65 20 4.02 0.4662
WVFGRD96 44.0 105 65 20 4.04 0.4768
WVFGRD96 46.0 105 65 20 4.06 0.4862
WVFGRD96 48.0 110 65 20 4.08 0.4962
WVFGRD96 50.0 110 65 20 4.10 0.5059
WVFGRD96 52.0 110 65 25 4.11 0.5159
WVFGRD96 54.0 110 65 25 4.12 0.5247
WVFGRD96 56.0 110 70 20 4.13 0.5327
WVFGRD96 58.0 110 70 25 4.14 0.5413
WVFGRD96 60.0 110 70 25 4.15 0.5492
WVFGRD96 62.0 110 70 25 4.16 0.5569
WVFGRD96 64.0 110 70 25 4.17 0.5631
WVFGRD96 66.0 110 70 25 4.18 0.5698
WVFGRD96 68.0 110 70 25 4.18 0.5746
WVFGRD96 70.0 110 70 25 4.19 0.5784
WVFGRD96 72.0 110 75 25 4.19 0.5830
WVFGRD96 74.0 110 75 25 4.20 0.5871
WVFGRD96 76.0 110 75 25 4.21 0.5904
WVFGRD96 78.0 110 75 25 4.21 0.5924
WVFGRD96 80.0 110 75 25 4.22 0.5940
WVFGRD96 82.0 110 75 25 4.22 0.5952
WVFGRD96 84.0 110 75 25 4.23 0.5962
WVFGRD96 86.0 110 75 25 4.23 0.5965
WVFGRD96 88.0 110 75 25 4.24 0.5960
WVFGRD96 90.0 110 80 25 4.24 0.5957
WVFGRD96 92.0 110 80 25 4.24 0.5956
WVFGRD96 94.0 110 80 25 4.25 0.5950
WVFGRD96 96.0 110 80 30 4.24 0.5942
WVFGRD96 98.0 110 80 30 4.25 0.5928
WVFGRD96 100.0 110 80 30 4.25 0.5912
WVFGRD96 102.0 110 80 30 4.26 0.5893
WVFGRD96 104.0 110 80 30 4.26 0.5873
WVFGRD96 106.0 110 80 30 4.26 0.5853
WVFGRD96 108.0 110 80 30 4.27 0.5831
WVFGRD96 110.0 110 80 30 4.27 0.5802
WVFGRD96 112.0 110 80 30 4.27 0.5772
WVFGRD96 114.0 110 85 30 4.27 0.5738
WVFGRD96 116.0 110 85 30 4.28 0.5710
WVFGRD96 118.0 110 85 35 4.27 0.5686
The best solution is
WVFGRD96 86.0 110 75 25 4.23 0.5965
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 a -30 a 180
rtr
taper w 0.1
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 Fri Apr 26 08:24:24 PM CDT 2024
