Location
2009/02/26 09:52:47 42.5440 -123.8920 37.8 4.10 Oregon
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports main page
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2009/02/26 09:52:47:0 42.54 -123.89 37.8 4.1 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
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 325
DIP = 70
RAKE = -75
MW = 4.19
HS = 43.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
PNSN |
USGS/SLU Moment Tensor Solution
ENS 2009/02/26 09:52:47:0 42.54 -123.89 37.8 4.1 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 |
Waveform Inversion
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the
and stations used for 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 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 from 0.5 to 19 km depth 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 17.0 335 90 -50 3.82 0.3134
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 correspond 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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 and because the velocity model used in the predictions may not be perfect.
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 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
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms.
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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Discussion
The Future
Should the national backbone of the
USGS Advanced National Seismic System (ANSS)
be implemented with an interstation separation of 300 km, it is very likely that
an earthquake such as this would have been recorded at distances on the order of
100-200 km. This means that the closest station would have information on
source depth and mechanism that was lacking here.
Acknowledgements
Dr. Harley Benz, USGS, provided the USGS USNSN digital data.
The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
Velocity Model
The WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Quality Control
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Thu Feb 26 14:20:26 CST 2009
Last Changed 2009/02/26