2010/08/17 09:22:20 43.623 -110.487 5.0 3.0 Wyoming
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2010/08/17 09:22:20:8 43.62 -110.49 5.0 3.0 Wyoming
Stations used:
IW.DLMT IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW
IW.TPAW US.BW06 UU.BGU UU.HVU UU.RDMU UU.SPU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.33e+21 dyne-cm
Mw = 3.35
Z = 7 km
Plane Strike Dip Rake
NP1 124 85 170
NP2 215 80 5
Principal Axes:
Axis Value Plunge Azimuth
T 1.33e+21 11 79
N 0.00e+00 79 278
P -1.33e+21 4 170
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.24e+21
Mxy 4.66e+20
Mxz 1.26e+20
Myy 1.20e+21
Myz 2.22e+20
Mzz 3.98e+19
--------------
----------------------
------------------------####
-----------------------#######
-----------------------###########
##---------------------#############
######----------------################
#########-------------##################
###########---------#################
###############-----################## T #
#################--################### #
#################---######################
################-------###################
##############-----------###############
#############---------------############
###########-------------------########
#########-----------------------####
#######---------------------------
####--------------------------
##--------------------------
------------- ------
--------- P --
Global CMT Convention Moment Tensor:
R T P
3.98e+19 1.26e+20 -2.22e+20
1.26e+20 -1.24e+21 -4.66e+20
-2.22e+20 -4.66e+20 1.20e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100817092220/index.html
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STK = 215
DIP = 80
RAKE = 5
MW = 3.35
HS = 7.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2010/08/17 09:22:20:8 43.62 -110.49 5.0 3.0 Wyoming
Stations used:
IW.DLMT IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW
IW.TPAW US.BW06 UU.BGU UU.HVU UU.RDMU UU.SPU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.33e+21 dyne-cm
Mw = 3.35
Z = 7 km
Plane Strike Dip Rake
NP1 124 85 170
NP2 215 80 5
Principal Axes:
Axis Value Plunge Azimuth
T 1.33e+21 11 79
N 0.00e+00 79 278
P -1.33e+21 4 170
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.24e+21
Mxy 4.66e+20
Mxz 1.26e+20
Myy 1.20e+21
Myz 2.22e+20
Mzz 3.98e+19
--------------
----------------------
------------------------####
-----------------------#######
-----------------------###########
##---------------------#############
######----------------################
#########-------------##################
###########---------#################
###############-----################## T #
#################--################### #
#################---######################
################-------###################
##############-----------###############
#############---------------############
###########-------------------########
#########-----------------------####
#######---------------------------
####--------------------------
##--------------------------
------------- ------
--------- P --
Global CMT Convention Moment Tensor:
R T P
3.98e+19 1.26e+20 -2.22e+20
1.26e+20 -1.24e+21 -4.66e+20
-2.22e+20 -4.66e+20 1.20e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100817092220/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 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 30 75 -60 3.08 0.4113
WVFGRD96 1.0 35 85 -40 3.04 0.4406
WVFGRD96 2.0 35 85 -45 3.21 0.5725
WVFGRD96 3.0 215 85 20 3.21 0.6285
WVFGRD96 4.0 215 75 10 3.24 0.6654
WVFGRD96 5.0 215 80 10 3.28 0.6874
WVFGRD96 6.0 215 80 10 3.31 0.6965
WVFGRD96 7.0 215 80 5 3.35 0.6974
WVFGRD96 8.0 215 80 10 3.39 0.6942
WVFGRD96 9.0 215 80 10 3.42 0.6774
WVFGRD96 10.0 215 80 10 3.44 0.6565
WVFGRD96 11.0 215 80 10 3.45 0.6340
WVFGRD96 12.0 215 80 10 3.46 0.6095
WVFGRD96 13.0 215 80 10 3.48 0.5845
WVFGRD96 14.0 215 80 10 3.49 0.5611
WVFGRD96 15.0 215 80 10 3.49 0.5398
WVFGRD96 16.0 215 80 10 3.50 0.5205
WVFGRD96 17.0 215 80 10 3.51 0.5048
WVFGRD96 18.0 215 80 10 3.52 0.4906
WVFGRD96 19.0 215 80 10 3.52 0.4795
WVFGRD96 20.0 215 80 10 3.53 0.4702
WVFGRD96 21.0 215 80 10 3.54 0.4602
WVFGRD96 22.0 215 80 10 3.54 0.4528
WVFGRD96 23.0 215 90 15 3.56 0.4463
WVFGRD96 24.0 35 90 -15 3.57 0.4431
WVFGRD96 25.0 35 90 -15 3.57 0.4402
WVFGRD96 26.0 35 90 -15 3.58 0.4410
WVFGRD96 27.0 30 80 -20 3.60 0.4424
WVFGRD96 28.0 30 80 -20 3.61 0.4450
WVFGRD96 29.0 30 80 -20 3.62 0.4488
The best solution is
WVFGRD96 7.0 215 80 5 3.35 0.6974
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
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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 Aug 17 07:48:50 MDT 2010