2008/08/30 22:06:15 41.6780 -111.1300 1.0 3.40 Utah
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/08/30 22:06:15 41.6780 -111.1300 1.0 3.40 Utah
Best Fitting Double Couple
Mo = 1.08e+21 dyne-cm
Mw = 3.29
Z = 10 km
Plane Strike Dip Rake
NP1 10 60 -125
NP2 245 45 -45
Principal Axes:
Axis Value Plunge Azimuth
T 1.08e+21 8 125
N 0.00e+00 30 30
P -1.08e+21 59 229
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.14e+20
Mxy -6.42e+20
Mxz 2.29e+20
Myy 5.52e+20
Myz 4.91e+20
Mzz -7.66e+20
###########---
#################-----
####################--------
######################--------
#################-------#####-----
#############-------------#########-
###########----------------###########
#########-------------------############
#######---------------------############
#######----------------------#############
#####------------------------#############
####-------------------------#############
###----------- -----------##############
##----------- P -----------#############
#------------ ----------##############
-------------------------######### #
-----------------------########## T
---------------------###########
------------------############
---------------#############
-----------###########
-----#########
Harvard Convention
Moment Tensor:
R T F
-7.66e+20 2.29e+20 -4.91e+20
2.29e+20 2.14e+20 6.42e+20
-4.91e+20 6.42e+20 5.52e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080830220615/index.html
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STK = 245
DIP = 45
RAKE = -45
MW = 3.29
HS = 10.0
This is a marginal solution. The moment and depth are well determined. The very small number of observed transverse components precludes a definitive solution. To provide more weight to the few transverse components, the Z and R traces were weighted 0.3 while the T was weighted 1.0, addition to the usual distance weight.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/08/30 22:06:15 41.6780 -111.1300 1.0 3.40 Utah
Best Fitting Double Couple
Mo = 1.08e+21 dyne-cm
Mw = 3.29
Z = 10 km
Plane Strike Dip Rake
NP1 10 60 -125
NP2 245 45 -45
Principal Axes:
Axis Value Plunge Azimuth
T 1.08e+21 8 125
N 0.00e+00 30 30
P -1.08e+21 59 229
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.14e+20
Mxy -6.42e+20
Mxz 2.29e+20
Myy 5.52e+20
Myz 4.91e+20
Mzz -7.66e+20
###########---
#################-----
####################--------
######################--------
#################-------#####-----
#############-------------#########-
###########----------------###########
#########-------------------############
#######---------------------############
#######----------------------#############
#####------------------------#############
####-------------------------#############
###----------- -----------##############
##----------- P -----------#############
#------------ ----------##############
-------------------------######### #
-----------------------########## T
---------------------###########
------------------############
---------------#############
-----------###########
-----#########
Harvard Convention
Moment Tensor:
R T F
-7.66e+20 2.29e+20 -4.91e+20
2.29e+20 2.14e+20 6.42e+20
-4.91e+20 6.42e+20 5.52e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080830220615/index.html
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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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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 0.10 n 3 br c 0.13 0.2 n 4 p 2The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 40 50 -90 2.87 0.1599
WVFGRD96 1.0 270 75 15 2.77 0.1482
WVFGRD96 2.0 200 45 -90 3.03 0.2297
WVFGRD96 3.0 90 60 20 3.03 0.2534
WVFGRD96 4.0 255 45 -25 3.11 0.2798
WVFGRD96 5.0 255 45 -25 3.15 0.3167
WVFGRD96 6.0 255 45 -25 3.18 0.3464
WVFGRD96 7.0 250 45 -35 3.21 0.3648
WVFGRD96 8.0 245 40 -45 3.28 0.3779
WVFGRD96 9.0 245 40 -45 3.29 0.3805
WVFGRD96 10.0 245 45 -45 3.29 0.3812
WVFGRD96 11.0 250 50 -35 3.28 0.3797
WVFGRD96 12.0 250 50 -35 3.29 0.3774
WVFGRD96 13.0 250 50 -35 3.30 0.3735
WVFGRD96 14.0 255 55 -30 3.30 0.3687
WVFGRD96 15.0 255 55 -30 3.31 0.3634
WVFGRD96 16.0 255 55 -30 3.32 0.3574
WVFGRD96 17.0 255 55 -30 3.32 0.3510
WVFGRD96 18.0 255 60 -30 3.32 0.3451
WVFGRD96 19.0 255 60 -30 3.33 0.3388
WVFGRD96 20.0 255 60 -30 3.34 0.3323
WVFGRD96 21.0 255 60 -30 3.35 0.3263
WVFGRD96 22.0 255 60 -35 3.36 0.3199
WVFGRD96 23.0 255 60 -35 3.36 0.3132
WVFGRD96 24.0 255 65 -35 3.36 0.3060
WVFGRD96 25.0 255 65 -35 3.36 0.2988
WVFGRD96 26.0 255 65 -35 3.37 0.2913
WVFGRD96 27.0 75 55 20 3.37 0.2840
WVFGRD96 28.0 75 55 20 3.38 0.2783
WVFGRD96 29.0 70 60 10 3.37 0.2737
WVFGRD96 30.0 70 60 10 3.37 0.2690
WVFGRD96 31.0 70 60 5 3.38 0.2640
WVFGRD96 32.0 70 60 10 3.39 0.2595
WVFGRD96 33.0 70 60 10 3.39 0.2553
WVFGRD96 34.0 70 60 10 3.40 0.2517
WVFGRD96 35.0 70 60 10 3.40 0.2490
WVFGRD96 36.0 70 60 15 3.41 0.2463
WVFGRD96 37.0 70 60 15 3.42 0.2449
WVFGRD96 38.0 70 60 20 3.44 0.2460
WVFGRD96 39.0 70 65 30 3.46 0.2484
WVFGRD96 40.0 85 50 50 3.55 0.2522
WVFGRD96 41.0 80 55 45 3.55 0.2556
WVFGRD96 42.0 80 55 45 3.56 0.2581
WVFGRD96 43.0 80 55 45 3.57 0.2598
WVFGRD96 44.0 80 55 45 3.58 0.2607
WVFGRD96 45.0 80 55 45 3.59 0.2619
WVFGRD96 46.0 80 55 45 3.60 0.2621
WVFGRD96 47.0 80 55 45 3.60 0.2622
WVFGRD96 48.0 80 55 50 3.62 0.2614
WVFGRD96 49.0 185 45 65 3.64 0.2604
WVFGRD96 50.0 185 45 65 3.65 0.2610
The best solution is
WVFGRD96 10.0 245 45 -45 3.29 0.3812
The mechanism correspond 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 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 0.10 n 3 br c 0.13 0.2 n 4 p 2
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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. |
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.
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.
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Tue Sep 2 08:45:23 CDT 2008