Location
Location ANSS
The ANSS event ID is ak0137t9n76d and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak0137t9n76d/executive.
2013/06/19 07:19:43 61.440 -149.835 48.6 4.3 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2013/06/19 07:19:43:0 61.44 -149.84 48.6 4.3 Alaska
Stations used:
AK.DIV AK.GHO AK.GLI AK.HIN AK.KNK AK.RC01 AK.SAW AK.SCM
AT.PMR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.60e+22 dyne-cm
Mw = 4.07
Z = 46 km
Plane Strike Dip Rake
NP1 215 50 -70
NP2 5 44 -112
Principal Axes:
Axis Value Plunge Azimuth
T 1.60e+22 3 291
N 0.00e+00 15 22
P -1.60e+22 74 190
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.34e+20
Mxy -5.53e+21
Mxz 4.39e+21
Myy 1.39e+22
Myz -1.21e+20
Mzz -1.48e+22
###########---
#################-----
##################---#######
###############--------#######
###############-----------########
#############--------------########
T ###########-----------------########
#########-------------------#########
###########--------------------#########
###########----------------------#########
##########-----------------------#########
#########---------- ----------##########
#########---------- P ----------##########
#######----------- ----------#########
#######-----------------------##########
######-----------------------#########
#####----------------------#########
####---------------------#########
##--------------------########
##-----------------#########
--------------########
--------######
Global CMT Convention Moment Tensor:
R T P
-1.48e+22 4.39e+21 1.21e+20
4.39e+21 9.34e+20 5.53e+21
1.21e+20 5.53e+21 1.39e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130619071943/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 = 215
DIP = 50
RAKE = -70
MW = 4.07
HS = 46.0
The NDK file is 20130619071943.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 2013/06/19 07:19:43:0 61.44 -149.84 48.6 4.3 Alaska
Stations used:
AK.DIV AK.GHO AK.GLI AK.HIN AK.KNK AK.RC01 AK.SAW AK.SCM
AT.PMR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.60e+22 dyne-cm
Mw = 4.07
Z = 46 km
Plane Strike Dip Rake
NP1 215 50 -70
NP2 5 44 -112
Principal Axes:
Axis Value Plunge Azimuth
T 1.60e+22 3 291
N 0.00e+00 15 22
P -1.60e+22 74 190
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.34e+20
Mxy -5.53e+21
Mxz 4.39e+21
Myy 1.39e+22
Myz -1.21e+20
Mzz -1.48e+22
###########---
#################-----
##################---#######
###############--------#######
###############-----------########
#############--------------########
T ###########-----------------########
#########-------------------#########
###########--------------------#########
###########----------------------#########
##########-----------------------#########
#########---------- ----------##########
#########---------- P ----------##########
#######----------- ----------#########
#######-----------------------##########
######-----------------------#########
#####----------------------#########
####---------------------#########
##--------------------########
##-----------------#########
--------------########
--------######
Global CMT Convention Moment Tensor:
R T P
-1.48e+22 4.39e+21 1.21e+20
4.39e+21 9.34e+20 5.53e+21
1.21e+20 5.53e+21 1.39e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130619071943/index.html
|
USGS/SLU Regional Moment Tensor Solution
Moment Tensor
Moment Tensor EQXML
Contributed Solutions
Moment Tensor
Contributed Moment Tensors
Contributor Code Type Magnitude Depth NP1 NP2
us usc000hutt-neic-mwr Mwr 4.1 51.0 km 210, 54, -65 352, 43, -120
us usc000hutt-neic-mwr
Type
Mwr
Moment
1.84e+15 N-m
Magnitude
4.1
Percent DC
98%
Depth
51.0 km
Author
neic
Updated
2013-06-19 07:58:46 UTC
Principal Axes
Axis Value Plunge Azimuth
T 1.833 6 282
N 0.013 20 15
P -1.846 69 177
Nodal Planes
Plane Strike Dip Rake
NP1 210 54 -65
NP2 352 43 -120
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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 0.10 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 195 50 90 3.22 0.2439
WVFGRD96 1.0 125 90 5 3.24 0.2408
WVFGRD96 2.0 130 75 25 3.39 0.3017
WVFGRD96 3.0 125 90 15 3.47 0.3182
WVFGRD96 4.0 120 65 -30 3.51 0.3249
WVFGRD96 5.0 120 65 -30 3.54 0.3408
WVFGRD96 6.0 125 70 -25 3.55 0.3476
WVFGRD96 7.0 340 70 40 3.49 0.3484
WVFGRD96 8.0 120 70 -20 3.66 0.3595
WVFGRD96 9.0 125 80 -20 3.67 0.3581
WVFGRD96 10.0 310 80 30 3.66 0.3554
WVFGRD96 11.0 310 80 30 3.68 0.3549
WVFGRD96 12.0 65 60 -35 3.63 0.3629
WVFGRD96 13.0 65 60 -30 3.64 0.3688
WVFGRD96 14.0 245 60 -30 3.66 0.3755
WVFGRD96 15.0 245 60 -30 3.68 0.3830
WVFGRD96 16.0 245 60 -30 3.69 0.3889
WVFGRD96 17.0 245 60 -30 3.71 0.3934
WVFGRD96 18.0 245 65 -30 3.72 0.3962
WVFGRD96 19.0 245 65 -30 3.74 0.3999
WVFGRD96 20.0 245 65 -30 3.75 0.4031
WVFGRD96 21.0 245 65 -30 3.76 0.4058
WVFGRD96 22.0 245 65 -30 3.77 0.4088
WVFGRD96 23.0 245 65 -25 3.77 0.4126
WVFGRD96 24.0 245 65 -30 3.79 0.4152
WVFGRD96 25.0 245 60 5 3.79 0.4253
WVFGRD96 26.0 240 60 5 3.81 0.4363
WVFGRD96 27.0 240 60 5 3.82 0.4462
WVFGRD96 28.0 240 55 0 3.82 0.4572
WVFGRD96 29.0 240 55 0 3.83 0.4650
WVFGRD96 30.0 230 55 -25 3.84 0.4755
WVFGRD96 31.0 230 55 -30 3.85 0.4896
WVFGRD96 32.0 230 55 -30 3.85 0.5046
WVFGRD96 33.0 225 50 -55 3.87 0.5184
WVFGRD96 34.0 225 50 -55 3.88 0.5385
WVFGRD96 35.0 225 50 -55 3.88 0.5527
WVFGRD96 36.0 225 50 -60 3.90 0.5675
WVFGRD96 37.0 220 50 -60 3.90 0.5753
WVFGRD96 38.0 220 50 -65 3.92 0.5832
WVFGRD96 39.0 220 50 -65 3.93 0.5903
WVFGRD96 40.0 220 50 -65 4.01 0.5999
WVFGRD96 41.0 220 50 -65 4.02 0.6063
WVFGRD96 42.0 215 50 -70 4.04 0.6134
WVFGRD96 43.0 215 50 -70 4.05 0.6177
WVFGRD96 44.0 215 50 -70 4.06 0.6222
WVFGRD96 45.0 215 50 -70 4.06 0.6228
WVFGRD96 46.0 215 50 -70 4.07 0.6250
WVFGRD96 47.0 215 50 -70 4.07 0.6225
WVFGRD96 48.0 215 50 -70 4.08 0.6226
WVFGRD96 49.0 215 55 -70 4.08 0.6205
WVFGRD96 50.0 215 55 -70 4.09 0.6183
WVFGRD96 51.0 215 55 -70 4.09 0.6169
WVFGRD96 52.0 215 55 -70 4.09 0.6145
WVFGRD96 53.0 215 55 -70 4.09 0.6123
WVFGRD96 54.0 215 55 -70 4.09 0.6090
WVFGRD96 55.0 215 55 -75 4.10 0.6064
WVFGRD96 56.0 210 55 -75 4.11 0.6028
WVFGRD96 57.0 215 55 -75 4.11 0.6012
WVFGRD96 58.0 210 55 -80 4.12 0.5986
WVFGRD96 59.0 210 55 -80 4.12 0.5950
The best solution is
WVFGRD96 46.0 215 50 -70 4.07 0.6250
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 0.10 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 06:03:38 PM CDT 2024
