The ANSS event ID is usb000qfvj and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usb000qfvj/executive.
2014/05/09 18:09:00 59.768 -136.599 15.4 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2014/05/09 18:09:00:0 59.77 -136.60 15.4 4.2 Alaska
Stations used:
AK.BAL AK.BARN AK.BESE AK.CRQ AK.CTG AK.DOT AK.EYAK AK.GLB
AK.HARP AK.JIS AK.MCAR AK.TGL AK.VRDI AK.YAH AT.SKAG
AT.YKU2 CN.DAWY CN.DLBC CN.HYT CN.WHY US.WRAK
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 7.76e+21 dyne-cm
Mw = 3.86
Z = 18 km
Plane Strike Dip Rake
NP1 265 75 20
NP2 170 71 164
Principal Axes:
Axis Value Plunge Azimuth
T 7.76e+21 25 128
N 0.00e+00 65 300
P -7.76e+21 3 37
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.54e+21
Mxy -6.82e+21
Mxz -2.13e+21
Myy 1.21e+21
Myz 2.08e+21
Mzz 1.33e+21
###-----------
######----------------
#########---------------- P
##########---------------- -
###########-----------------------
############------------------------
#############-------------------------
##############--------------------------
##############--------------------------
#############---#######################---
######----------##########################
##--------------##########################
-----------------#########################
----------------########################
----------------########################
----------------############## #####
----------------############# T ####
---------------############# ###
--------------################
--------------##############
------------##########
----------####
Global CMT Convention Moment Tensor:
R T P
1.33e+21 -2.13e+21 -2.08e+21
-2.13e+21 -2.54e+21 6.82e+21
-2.08e+21 6.82e+21 1.21e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140509180900/index.html
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STK = 265
DIP = 75
RAKE = 20
MW = 3.86
HS = 18.0
The NDK file is 20140509180900.ndk The waveform inversion is preferred.
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.
USGS/SLU Moment Tensor Solution
ENS 2014/05/09 18:09:00:0 59.77 -136.60 15.4 4.2 Alaska
Stations used:
AK.BAL AK.BARN AK.BESE AK.CRQ AK.CTG AK.DOT AK.EYAK AK.GLB
AK.HARP AK.JIS AK.MCAR AK.TGL AK.VRDI AK.YAH AT.SKAG
AT.YKU2 CN.DAWY CN.DLBC CN.HYT CN.WHY US.WRAK
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 7.76e+21 dyne-cm
Mw = 3.86
Z = 18 km
Plane Strike Dip Rake
NP1 265 75 20
NP2 170 71 164
Principal Axes:
Axis Value Plunge Azimuth
T 7.76e+21 25 128
N 0.00e+00 65 300
P -7.76e+21 3 37
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.54e+21
Mxy -6.82e+21
Mxz -2.13e+21
Myy 1.21e+21
Myz 2.08e+21
Mzz 1.33e+21
###-----------
######----------------
#########---------------- P
##########---------------- -
###########-----------------------
############------------------------
#############-------------------------
##############--------------------------
##############--------------------------
#############---#######################---
######----------##########################
##--------------##########################
-----------------#########################
----------------########################
----------------########################
----------------############## #####
----------------############# T ####
---------------############# ###
--------------################
--------------##############
------------##########
----------####
Global CMT Convention Moment Tensor:
R T P
1.33e+21 -2.13e+21 -2.08e+21
-2.13e+21 -2.54e+21 6.82e+21
-2.08e+21 6.82e+21 1.21e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140509180900/index.html
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Moment magnitude derived from a moment tensor
inversion of complete waveforms at regional
distances (less than ~8 degrees), generally used
for the analysis of small to moderate size
earthquakes (typically Mw 3.5-6.0) crust or
upper mantle earthquakes.
Moment
8.15e+14 N-m
Magnitude
3.9
Percent DC
96%
Depth
20.0 km
Updated
2014-05-09 18:23:54 UTC
Author
us
Catalog
us
Contributor
us
Code
us_b000qfvj_mwr
Principal Axes
Axis Value Plunge Azimuth
T 8.211 21 129
N -0.131 69 316
P -8.080 2 220
Nodal Planes
Plane Strike Dip Rake
NP1 172 77 163
NP2 266 73 14
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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.
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.
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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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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 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 85 90 -5 3.41 0.2911
WVFGRD96 2.0 80 75 -20 3.52 0.3622
WVFGRD96 3.0 80 70 -20 3.58 0.3913
WVFGRD96 4.0 80 75 -25 3.62 0.3959
WVFGRD96 5.0 80 80 -25 3.64 0.3911
WVFGRD96 6.0 265 80 30 3.67 0.4074
WVFGRD96 7.0 265 65 15 3.69 0.4323
WVFGRD96 8.0 270 60 20 3.74 0.4597
WVFGRD96 9.0 270 60 20 3.76 0.4841
WVFGRD96 10.0 270 65 25 3.77 0.5056
WVFGRD96 11.0 270 65 25 3.79 0.5245
WVFGRD96 12.0 270 65 25 3.80 0.5398
WVFGRD96 13.0 265 70 20 3.82 0.5516
WVFGRD96 14.0 265 70 20 3.83 0.5617
WVFGRD96 15.0 265 70 20 3.83 0.5684
WVFGRD96 16.0 265 70 20 3.84 0.5726
WVFGRD96 17.0 265 70 20 3.85 0.5743
WVFGRD96 18.0 265 75 20 3.86 0.5743
WVFGRD96 19.0 265 75 20 3.87 0.5736
WVFGRD96 20.0 265 75 20 3.88 0.5712
WVFGRD96 21.0 265 75 25 3.88 0.5677
WVFGRD96 22.0 265 75 25 3.89 0.5631
WVFGRD96 23.0 265 75 25 3.90 0.5575
WVFGRD96 24.0 265 75 25 3.90 0.5510
WVFGRD96 25.0 265 75 25 3.91 0.5441
WVFGRD96 26.0 265 75 25 3.92 0.5367
WVFGRD96 27.0 265 75 25 3.92 0.5286
WVFGRD96 28.0 265 75 25 3.93 0.5201
WVFGRD96 29.0 265 75 25 3.94 0.5110
The best solution is
WVFGRD96 18.0 265 75 20 3.86 0.5743
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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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 0.06 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. |
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:
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.
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