The ANSS event ID is uw10609208 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw10609208/executive.
2004/07/12 16:45:00 44.334 -124.489 28.8 4.9 Oregon
USGS/SLU Moment Tensor Solution
ENS 2004/07/12 16:45:00:0 44.33 -124.49 28.8 4.9 Oregon
Stations used:
BK.HOPS BK.HUMO BK.JCC BK.MOD BK.ORV BK.YBH UO.EUO UO.PIN
US.HAWA US.WVOR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.27e+23 dyne-cm
Mw = 4.67
Z = 15 km
Plane Strike Dip Rake
NP1 186 71 97
NP2 345 20 70
Principal Axes:
Axis Value Plunge Azimuth
T 1.27e+23 63 107
N 0.00e+00 7 4
P -1.27e+23 26 271
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.30e+21
Mxy -6.33e+21
Mxz -1.58e+22
Myy -7.92e+22
Myz 9.91e+22
Mzz 7.69e+22
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---- P ---------######################----
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Global CMT Convention Moment Tensor:
R T P
7.69e+22 -1.58e+22 -9.91e+22
-1.58e+22 2.30e+21 6.33e+21
-9.91e+22 6.33e+21 -7.92e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20040712164500/index.html
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STK = 345
DIP = 20
RAKE = 70
MW = 4.67
HS = 15.0
The NDK file is 20040712164500.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 2004/07/12 16:45:00:0 44.33 -124.49 28.8 4.9 Oregon
Stations used:
BK.HOPS BK.HUMO BK.JCC BK.MOD BK.ORV BK.YBH UO.EUO UO.PIN
US.HAWA US.WVOR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.27e+23 dyne-cm
Mw = 4.67
Z = 15 km
Plane Strike Dip Rake
NP1 186 71 97
NP2 345 20 70
Principal Axes:
Axis Value Plunge Azimuth
T 1.27e+23 63 107
N 0.00e+00 7 4
P -1.27e+23 26 271
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.30e+21
Mxy -6.33e+21
Mxz -1.58e+22
Myy -7.92e+22
Myz 9.91e+22
Mzz 7.69e+22
--------------
-----------######-----
-------------##########-----
-------------#############----
---------------##############-----
---------------#################----
----------------##################----
----------------####################----
----------------####################----
---- ----------#####################----
---- P ---------######################----
---- ---------########## #########----
----------------########## T #########----
---------------########## #########---
---------------#####################----
--------------#####################---
-------------####################---
------------###################---
-----------#################--
----------###############---
-------#############--
----##########
Global CMT Convention Moment Tensor:
R T P
7.69e+22 -1.58e+22 -9.91e+22
-1.58e+22 2.30e+21 6.33e+21
-9.91e+22 6.33e+21 -7.92e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20040712164500/index.html
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071204B NEAR COAST OF OREGON
Date: 2004/ 7/12 Centroid Time: 16:45: 3.7 GMT
Lat= 44.30 Lon=-124.71
Depth= 20.0 Half duration= 0.7
Centroid time minus hypocenter time: 3.0
Moment Tensor: Expo=23 1.960 0.051 -2.010 0.254 -1.650 -0.397
Mw = 4.9 mb = 4.9 Ms = 4.1 Scalar Moment = 2.62e+23
Fault plane: strike=23 dip=27 slip=112
Fault plane: strike=178 dip=65 slip=79
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ofor04194 0 07/12/2004 16:45:00.0 44.332 -124.520 4.9 29.1 7121645
2 191 58 100 353 34 74 8 0.0 2.15e23 4.8 3
-2 0.02 0.05 OT01 OT04 OT06 OT08 HUMO YBH (uw7121645)
STK 191
DIP 59
RAKE 100
Mo=2.15E+23 dyne-cm
Mw=4.8
H=8
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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:
hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 20 45 -95 4.19 0.2135
WVFGRD96 1.0 20 45 -95 4.25 0.2047
WVFGRD96 2.0 20 45 -95 4.38 0.2428
WVFGRD96 3.0 225 20 -60 4.41 0.1521
WVFGRD96 4.0 255 10 -30 4.41 0.2057
WVFGRD96 5.0 270 10 -15 4.42 0.2631
WVFGRD96 6.0 280 10 0 4.43 0.3137
WVFGRD96 7.0 295 10 15 4.44 0.3539
WVFGRD96 8.0 305 10 25 4.54 0.3837
WVFGRD96 9.0 325 15 45 4.56 0.4206
WVFGRD96 10.0 340 20 60 4.59 0.4543
WVFGRD96 11.0 345 20 65 4.61 0.4854
WVFGRD96 12.0 350 20 75 4.63 0.5079
WVFGRD96 13.0 350 25 70 4.65 0.5242
WVFGRD96 14.0 350 20 75 4.66 0.5322
WVFGRD96 15.0 345 20 70 4.67 0.5344
WVFGRD96 16.0 345 20 65 4.68 0.5328
WVFGRD96 17.0 345 20 65 4.69 0.5261
WVFGRD96 18.0 340 15 60 4.69 0.5162
WVFGRD96 19.0 340 15 60 4.71 0.5062
WVFGRD96 20.0 340 15 60 4.72 0.4943
WVFGRD96 21.0 335 15 55 4.74 0.4818
WVFGRD96 22.0 325 15 45 4.75 0.4670
WVFGRD96 23.0 335 10 55 4.75 0.4525
WVFGRD96 24.0 330 10 50 4.76 0.4371
WVFGRD96 25.0 330 10 50 4.77 0.4203
WVFGRD96 26.0 330 10 50 4.78 0.4021
WVFGRD96 27.0 330 10 50 4.79 0.3824
WVFGRD96 28.0 325 10 45 4.79 0.3608
WVFGRD96 29.0 325 10 45 4.80 0.3374
The best solution is
WVFGRD96 15.0 345 20 70 4.67 0.5344
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
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. |
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