The program elocate was used with the WUS model to locate this earthquake. Because of the small number of good quality first arrivals, the location is not the best. The SLU location is elocate.txt. This location is preferred because of the smaller time shifts with respect the WUS model predicted P-wave first arrival time in the waveform modeling that for the NEIC location. The SH pulses were the best signal. The NEIC lcoation required the predicted trace to be shifted 2.25, -4.00, -6.25 -3.50 seconds for the stations PLID, MFID, HLID and DLMT, which the SLU location required times shifts of -1.25, 0.25, -1.00 and -0.25 seconds. The SLU location is preferred on the basis of the waveforms fit.
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2010/08/21 14:54:49:7 44.27 -115.42 10.0 3.6 Idaho
Stations used:
IW.DLMT IW.FLWY IW.FXWY IW.LOHW IW.MFID IW.PLID IW.TPAW
US.HLID
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.58e+21 dyne-cm
Mw = 3.40
Z = 9 km
Plane Strike Dip Rake
NP1 340 80 -45
NP2 80 46 -166
Principal Axes:
Axis Value Plunge Azimuth
T 1.58e+21 22 37
N 0.00e+00 44 150
P -1.58e+21 38 289
Moment Tensor: (dyne-cm)
Component Value
Mxx 7.54e+20
Mxy 9.69e+20
Mxz 1.77e+20
Myy -3.71e+20
Myz 1.06e+21
Mzz -3.83e+20
##############
-----#################
----------############ ###
------------########### T ####
---------------########## ######
-----------------###################
------------------####################
------ -----------####################
------ P ------------###################
------- -------------##################-
-----------------------#################--
------------------------###############---
-------------------------#############----
------------------------###########-----
##-----------------------########-------
####--------------------#####---------
#######----------------#------------
#######################-----------
######################--------
#####################-------
##################----
##############
Global CMT Convention Moment Tensor:
R T P
-3.83e+20 1.77e+20 -1.06e+21
1.77e+20 7.54e+20 -9.69e+20
-1.06e+21 -9.69e+20 -3.71e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100821145449/index.html
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STK = 340
DIP = 80
RAKE = -45
MW = 3.40
HS = 9.0
The waveform inversion with the SLU location is preferred. The second pass at the inversion dropped some Z and R channels which seem to have been noise.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2010/08/21 14:54:49:7 44.27 -115.42 10.0 3.6 Idaho
Stations used:
IW.DLMT IW.FLWY IW.FXWY IW.LOHW IW.MFID IW.PLID IW.TPAW
US.HLID
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.58e+21 dyne-cm
Mw = 3.40
Z = 9 km
Plane Strike Dip Rake
NP1 340 80 -45
NP2 80 46 -166
Principal Axes:
Axis Value Plunge Azimuth
T 1.58e+21 22 37
N 0.00e+00 44 150
P -1.58e+21 38 289
Moment Tensor: (dyne-cm)
Component Value
Mxx 7.54e+20
Mxy 9.69e+20
Mxz 1.77e+20
Myy -3.71e+20
Myz 1.06e+21
Mzz -3.83e+20
##############
-----#################
----------############ ###
------------########### T ####
---------------########## ######
-----------------###################
------------------####################
------ -----------####################
------ P ------------###################
------- -------------##################-
-----------------------#################--
------------------------###############---
-------------------------#############----
------------------------###########-----
##-----------------------########-------
####--------------------#####---------
#######----------------#------------
#######################-----------
######################--------
#####################-------
##################----
##############
Global CMT Convention Moment Tensor:
R T P
-3.83e+20 1.77e+20 -1.06e+21
1.77e+20 7.54e+20 -9.69e+20
-1.06e+21 -9.69e+20 -3.71e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100821145449/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 0.12 0.25 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 0.5 175 65 35 2.91 0.2062
WVFGRD96 1.0 170 85 5 2.92 0.2360
WVFGRD96 2.0 345 85 0 3.11 0.4178
WVFGRD96 3.0 345 85 -5 3.18 0.4793
WVFGRD96 4.0 165 90 20 3.23 0.5068
WVFGRD96 5.0 345 80 -25 3.27 0.5298
WVFGRD96 6.0 345 85 -35 3.31 0.5418
WVFGRD96 7.0 345 85 -35 3.33 0.5492
WVFGRD96 8.0 340 80 -45 3.39 0.5528
WVFGRD96 9.0 340 80 -45 3.40 0.5531
WVFGRD96 10.0 340 80 -45 3.42 0.5510
WVFGRD96 11.0 340 80 -45 3.43 0.5468
WVFGRD96 12.0 340 80 -40 3.42 0.5421
WVFGRD96 13.0 165 90 -40 3.44 0.5385
WVFGRD96 14.0 165 90 -40 3.45 0.5353
WVFGRD96 15.0 165 90 -35 3.44 0.5328
WVFGRD96 16.0 165 90 -35 3.45 0.5304
WVFGRD96 17.0 165 90 -35 3.46 0.5281
WVFGRD96 18.0 165 90 -35 3.47 0.5254
WVFGRD96 19.0 165 90 -35 3.48 0.5224
WVFGRD96 20.0 165 90 -30 3.48 0.5203
WVFGRD96 21.0 165 90 -30 3.49 0.5184
WVFGRD96 22.0 165 90 -30 3.50 0.5164
WVFGRD96 23.0 165 90 -30 3.51 0.5139
WVFGRD96 24.0 165 90 -30 3.52 0.5110
WVFGRD96 25.0 165 90 -30 3.52 0.5077
WVFGRD96 26.0 165 85 -25 3.52 0.5036
WVFGRD96 27.0 345 80 10 3.51 0.5002
WVFGRD96 28.0 345 90 30 3.55 0.4950
WVFGRD96 29.0 345 90 30 3.55 0.4894
The best solution is
WVFGRD96 9.0 340 80 -45 3.40 0.5531
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 0.12 0.25 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=Sat Aug 21 13:08:58 CDT 2010