Location
Location ANSS
The ANSS event ID is uw10762533 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/uw10762533/executive.
2009/02/26 09:52:47 42.541 -123.896 36.8 4.24 Oregon
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2009/02/26 09:52:47:0 42.54 -123.90 36.8 4.2 Oregon
Stations used:
BK.HUMO BK.WDC NC.KRMB UO.PIN US.BMO UW.LCCR UW.TREE
UW.UMAT UW.YACT
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.43e+22 dyne-cm
Mw = 4.19
Z = 43 km
Plane Strike Dip Rake
NP1 325 70 -75
NP2 107 25 -125
Principal Axes:
Axis Value Plunge Azimuth
T 2.43e+22 24 43
N 0.00e+00 14 140
P -2.43e+22 62 258
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+22
Mxy 9.10e+21
Mxz 8.54e+21
Myy 4.56e+21
Myz 1.59e+22
Mzz -1.51e+22
##############
######################
-----#######################
---------################ ##
-------------############## T ####
----------------############ #####
-------------------###################
---------------------###################
-----------------------#################
#------------------------#################
#------------ -----------###############
##----------- P ------------##############
###---------- -------------#############
##---------------------------###########
####-------------------------###########
####-------------------------########-
#####------------------------######-
######----------------------####--
#######-----------------------
############--------######--
######################
##############
Global CMT Convention Moment Tensor:
R T P
-1.51e+22 8.54e+21 -1.59e+22
8.54e+21 1.05e+22 -9.10e+21
-1.59e+22 -9.10e+21 4.56e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090226095247/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 = 325
DIP = 70
RAKE = -75
MW = 4.19
HS = 43.0
The NDK file is 20090226095247.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 |
PNSN |
USGS/SLU Moment Tensor Solution
ENS 2009/02/26 09:52:47:0 42.54 -123.90 36.8 4.2 Oregon
Stations used:
BK.HUMO BK.WDC NC.KRMB UO.PIN US.BMO UW.LCCR UW.TREE
UW.UMAT UW.YACT
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.43e+22 dyne-cm
Mw = 4.19
Z = 43 km
Plane Strike Dip Rake
NP1 325 70 -75
NP2 107 25 -125
Principal Axes:
Axis Value Plunge Azimuth
T 2.43e+22 24 43
N 0.00e+00 14 140
P -2.43e+22 62 258
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+22
Mxy 9.10e+21
Mxz 8.54e+21
Myy 4.56e+21
Myz 1.59e+22
Mzz -1.51e+22
##############
######################
-----#######################
---------################ ##
-------------############## T ####
----------------############ #####
-------------------###################
---------------------###################
-----------------------#################
#------------------------#################
#------------ -----------###############
##----------- P ------------##############
###---------- -------------#############
##---------------------------###########
####-------------------------###########
####-------------------------########-
#####------------------------######-
######----------------------####--
#######-----------------------
############--------######--
######################
##############
Global CMT Convention Moment Tensor:
R T P
-1.51e+22 8.54e+21 -1.59e+22
8.54e+21 1.05e+22 -9.10e+21
-1.59e+22 -9.10e+21 4.56e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090226095247/index.html
|
Fault Plane Parameters for 09022609524k
Fault Choice 1 Fault Choice 2
Strike(deg) 120.0 330.0
Dip(deg) 50.0 44.0
Rake(deg) -110.3 -67.5
Fault Type normal normal
PNSN Notable Quake link for this earthquake
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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 0.06 n 3
br c 0.12 0.25 n 4 p 2
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 320 75 15 3.60 0.2469
WVFGRD96 1.0 320 75 10 3.63 0.2604
WVFGRD96 2.0 320 75 10 3.71 0.2941
WVFGRD96 3.0 320 70 10 3.76 0.3052
WVFGRD96 4.0 320 70 10 3.80 0.3033
WVFGRD96 5.0 320 70 10 3.82 0.2917
WVFGRD96 6.0 315 65 -5 3.84 0.2788
WVFGRD96 7.0 315 60 -10 3.84 0.2687
WVFGRD96 8.0 155 75 55 3.84 0.2638
WVFGRD96 9.0 155 75 55 3.83 0.2626
WVFGRD96 10.0 160 75 55 3.81 0.2654
WVFGRD96 11.0 155 80 50 3.81 0.2697
WVFGRD96 12.0 160 80 55 3.80 0.2761
WVFGRD96 13.0 160 80 55 3.80 0.2832
WVFGRD96 14.0 160 80 55 3.80 0.2902
WVFGRD96 15.0 165 80 55 3.80 0.2975
WVFGRD96 16.0 160 85 55 3.80 0.3060
WVFGRD96 17.0 160 85 55 3.81 0.3142
WVFGRD96 18.0 330 85 -50 3.83 0.3228
WVFGRD96 19.0 330 80 -50 3.84 0.3330
WVFGRD96 20.0 330 80 -55 3.84 0.3439
WVFGRD96 21.0 325 75 -55 3.87 0.3543
WVFGRD96 22.0 325 75 -55 3.88 0.3670
WVFGRD96 23.0 325 70 -55 3.89 0.3807
WVFGRD96 24.0 325 70 -55 3.91 0.3940
WVFGRD96 25.0 325 70 -55 3.92 0.4066
WVFGRD96 26.0 325 70 -60 3.93 0.4188
WVFGRD96 27.0 325 70 -60 3.94 0.4306
WVFGRD96 28.0 325 70 -60 3.95 0.4416
WVFGRD96 29.0 325 70 -60 3.96 0.4516
WVFGRD96 30.0 325 70 -65 3.97 0.4606
WVFGRD96 31.0 325 70 -65 3.98 0.4689
WVFGRD96 32.0 325 65 -65 3.99 0.4764
WVFGRD96 33.0 325 65 -65 4.00 0.4835
WVFGRD96 34.0 325 65 -65 4.01 0.4892
WVFGRD96 35.0 325 65 -65 4.02 0.4942
WVFGRD96 36.0 325 65 -65 4.02 0.4985
WVFGRD96 37.0 325 65 -65 4.03 0.5018
WVFGRD96 38.0 325 65 -65 4.04 0.5050
WVFGRD96 39.0 320 60 -70 4.07 0.5082
WVFGRD96 40.0 325 70 -75 4.17 0.5040
WVFGRD96 41.0 325 70 -75 4.18 0.5068
WVFGRD96 42.0 325 70 -75 4.18 0.5084
WVFGRD96 43.0 325 70 -75 4.19 0.5089
WVFGRD96 44.0 320 65 -75 4.20 0.5088
WVFGRD96 45.0 320 65 -75 4.20 0.5083
WVFGRD96 46.0 320 65 -75 4.21 0.5068
WVFGRD96 47.0 320 65 -75 4.21 0.5048
WVFGRD96 48.0 325 65 -75 4.22 0.5021
WVFGRD96 49.0 320 65 -75 4.22 0.4986
WVFGRD96 50.0 325 65 -70 4.22 0.4948
WVFGRD96 51.0 320 65 -75 4.23 0.4903
WVFGRD96 52.0 320 65 -75 4.23 0.4850
WVFGRD96 53.0 325 65 -70 4.23 0.4798
WVFGRD96 54.0 325 65 -70 4.23 0.4742
WVFGRD96 55.0 325 65 -70 4.23 0.4679
WVFGRD96 56.0 325 65 -70 4.23 0.4617
WVFGRD96 57.0 325 65 -70 4.23 0.4549
WVFGRD96 58.0 325 65 -70 4.24 0.4481
WVFGRD96 59.0 325 65 -70 4.24 0.4417
WVFGRD96 60.0 325 65 -70 4.24 0.4348
The best solution is
WVFGRD96 43.0 325 70 -75 4.19 0.5089
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 0.06 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.
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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 Sun Apr 28 01:07:48 PM CDT 2024
