The ANSS event ID is uw10826768 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw10826768/executive.
2011/07/24 12:19:28 47.708 -123.178 40.6 3.85 Washington
USGS/SLU Moment Tensor Solution
ENS 2011/07/24 12:19:28:0 47.71 -123.18 40.6 3.8 Washington
Stations used:
IU.COR UW.DAVN UW.LEBA UW.LON UW.LTY UW.MRBL UW.OMAK
UW.STOR UW.TUCA UW.WOLL UW.YACT
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 6.10e+21 dyne-cm
Mw = 3.79
Z = 45 km
Plane Strike Dip Rake
NP1 285 50 -60
NP2 63 48 -121
Principal Axes:
Axis Value Plunge Azimuth
T 6.10e+21 1 354
N 0.00e+00 23 85
P -6.10e+21 67 262
Moment Tensor: (dyne-cm)
Component Value
Mxx 6.02e+21
Mxy -7.22e+20
Mxz 3.78e+20
Myy -8.19e+20
Myz 2.13e+21
Mzz -5.20e+21
### T ########
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############################
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##################################
#######------------#################
###-----------------------###########-
#-----------------------------########--
---------------------------------#####--
------------------------------------##----
-------------- --------------------#----
-------------- P -------------------###---
-------------- -----------------######--
-------------------------------#########
-----------------------------###########
-------------------------#############
#--------------------###############
#####---------####################
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Global CMT Convention Moment Tensor:
R T P
-5.20e+21 3.78e+20 -2.13e+21
3.78e+20 6.02e+21 7.22e+20
-2.13e+21 7.22e+20 -8.19e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110724121928/index.html
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STK = 285
DIP = 50
RAKE = -60
MW = 3.79
HS = 45.0
The NDK file is 20110724121928.ndk The waveform inversion is preferred.
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 o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 260 45 95 3.13 0.3618
WVFGRD96 1.0 255 45 90 3.16 0.3513
WVFGRD96 2.0 250 40 80 3.25 0.4247
WVFGRD96 3.0 250 40 80 3.30 0.4273
WVFGRD96 4.0 245 50 70 3.33 0.4142
WVFGRD96 5.0 240 55 65 3.34 0.4064
WVFGRD96 6.0 50 70 55 3.32 0.4017
WVFGRD96 7.0 50 70 50 3.31 0.3981
WVFGRD96 8.0 55 70 65 3.38 0.4076
WVFGRD96 9.0 60 65 70 3.39 0.4089
WVFGRD96 10.0 60 65 65 3.38 0.4106
WVFGRD96 11.0 55 65 60 3.37 0.4151
WVFGRD96 12.0 60 60 60 3.38 0.4282
WVFGRD96 13.0 55 60 55 3.38 0.4404
WVFGRD96 14.0 55 60 50 3.39 0.4507
WVFGRD96 15.0 55 60 50 3.39 0.4592
WVFGRD96 16.0 55 60 45 3.40 0.4662
WVFGRD96 17.0 55 60 45 3.41 0.4721
WVFGRD96 18.0 55 60 45 3.42 0.4767
WVFGRD96 19.0 50 65 40 3.42 0.4801
WVFGRD96 20.0 50 65 40 3.43 0.4831
WVFGRD96 21.0 55 65 45 3.44 0.4856
WVFGRD96 22.0 105 50 -45 3.44 0.4903
WVFGRD96 23.0 105 50 -45 3.45 0.4977
WVFGRD96 24.0 110 55 -40 3.46 0.5048
WVFGRD96 25.0 110 50 -40 3.47 0.5118
WVFGRD96 26.0 295 55 -40 3.49 0.5277
WVFGRD96 27.0 295 55 -40 3.50 0.5418
WVFGRD96 28.0 300 60 -40 3.52 0.5561
WVFGRD96 29.0 300 60 -40 3.53 0.5701
WVFGRD96 30.0 300 60 -40 3.54 0.5834
WVFGRD96 31.0 300 60 -40 3.55 0.5959
WVFGRD96 32.0 300 60 -40 3.57 0.6076
WVFGRD96 33.0 300 60 -40 3.58 0.6187
WVFGRD96 34.0 300 60 -40 3.59 0.6293
WVFGRD96 35.0 300 60 -40 3.60 0.6390
WVFGRD96 36.0 300 60 -40 3.61 0.6477
WVFGRD96 37.0 295 55 -45 3.62 0.6561
WVFGRD96 38.0 295 55 -45 3.64 0.6637
WVFGRD96 39.0 290 55 -50 3.65 0.6709
WVFGRD96 40.0 290 50 -55 3.74 0.6873
WVFGRD96 41.0 290 50 -55 3.75 0.6924
WVFGRD96 42.0 290 50 -55 3.76 0.6956
WVFGRD96 43.0 285 50 -55 3.77 0.6975
WVFGRD96 44.0 285 50 -60 3.78 0.6986
WVFGRD96 45.0 285 50 -60 3.79 0.6986
WVFGRD96 46.0 285 50 -60 3.79 0.6970
WVFGRD96 47.0 285 50 -60 3.80 0.6941
WVFGRD96 48.0 280 50 -60 3.80 0.6909
WVFGRD96 49.0 280 50 -65 3.81 0.6870
WVFGRD96 50.0 280 50 -65 3.82 0.6825
WVFGRD96 51.0 280 50 -65 3.82 0.6769
WVFGRD96 52.0 275 50 -65 3.83 0.6711
WVFGRD96 53.0 275 50 -70 3.84 0.6655
WVFGRD96 54.0 275 50 -70 3.84 0.6589
WVFGRD96 55.0 275 50 -70 3.84 0.6516
WVFGRD96 56.0 270 50 -75 3.85 0.6439
WVFGRD96 57.0 270 50 -75 3.85 0.6371
WVFGRD96 58.0 270 50 -75 3.86 0.6296
WVFGRD96 59.0 270 50 -75 3.86 0.6217
WVFGRD96 60.0 275 55 -65 3.85 0.6147
WVFGRD96 61.0 275 55 -70 3.86 0.6081
WVFGRD96 62.0 270 55 -70 3.86 0.6021
WVFGRD96 63.0 270 55 -70 3.86 0.5961
WVFGRD96 64.0 270 55 -75 3.87 0.5898
WVFGRD96 65.0 325 75 -50 3.86 0.5798
WVFGRD96 66.0 325 75 -50 3.87 0.5782
WVFGRD96 67.0 325 75 -50 3.87 0.5762
WVFGRD96 68.0 325 75 -50 3.87 0.5738
WVFGRD96 69.0 325 75 -50 3.87 0.5711
The best solution is
WVFGRD96 45.0 285 50 -60 3.79 0.6986
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 o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2
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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