2008/10/18 02:27:38 36.1450 -114.5810 10.0 3.30 Arizona
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/10/18 02:27:38 36.1450 -114.5810 10.0 3.30 Arizona
Best Fitting Double Couple
Mo = 1.64e+21 dyne-cm
Mw = 3.41
Z = 7 km
Plane Strike Dip Rake
NP1 205 81 150
NP2 300 60 10
Principal Axes:
Axis Value Plunge Azimuth
T 1.64e+21 27 158
N 0.00e+00 59 11
P -1.64e+21 14 256
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.03e+21
Mxy -8.06e+20
Mxz -5.27e+20
Myy -1.27e+21
Myz 6.28e+20
Mzz 2.47e+20
##############
###################---
####################--------
####################----------
#####################-------------
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-------------------##-----------------
---------------------###----------------
--------------------#######-------------
--------------------##########------------
-------------------#############----------
------------------################--------
-- ------------###################------
- P ------------####################----
- -----------######################---
-------------#######################--
-----------#########################
----------########### ##########
-------############ T ########
------############ #######
--####################
##############
Harvard Convention
Moment Tensor:
R T F
2.47e+20 -5.27e+20 -6.28e+20
-5.27e+20 1.03e+21 8.06e+20
-6.28e+20 8.06e+20 -1.27e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081018022738/index.html
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STK = 300
DIP = 60
RAKE = 10
MW = 3.41
HS = 7.0
The waveform inversion is preferred. This is a marginal solution. The depth, moment magnitude and pressure and tension axes are fairly robust, but the nodal plane dips can vary.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/10/18 02:27:38 36.1450 -114.5810 10.0 3.30 Arizona
Best Fitting Double Couple
Mo = 1.64e+21 dyne-cm
Mw = 3.41
Z = 7 km
Plane Strike Dip Rake
NP1 205 81 150
NP2 300 60 10
Principal Axes:
Axis Value Plunge Azimuth
T 1.64e+21 27 158
N 0.00e+00 59 11
P -1.64e+21 14 256
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.03e+21
Mxy -8.06e+20
Mxz -5.27e+20
Myy -1.27e+21
Myz 6.28e+20
Mzz 2.47e+20
##############
###################---
####################--------
####################----------
#####################-------------
-------------########---------------
-------------------##-----------------
---------------------###----------------
--------------------#######-------------
--------------------##########------------
-------------------#############----------
------------------################--------
-- ------------###################------
- P ------------####################----
- -----------######################---
-------------#######################--
-----------#########################
----------########### ##########
-------############ T ########
------############ #######
--####################
##############
Harvard Convention
Moment Tensor:
R T F
2.47e+20 -5.27e+20 -6.28e+20
-5.27e+20 1.03e+21 8.06e+20
-6.28e+20 8.06e+20 -1.27e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081018022738/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 0.06 n 3 br c 0.12 0.25 n 4 p 2 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 0.5 295 75 -20 3.22 0.4412
WVFGRD96 1.0 295 75 -15 3.23 0.4639
WVFGRD96 2.0 295 75 -20 3.30 0.5279
WVFGRD96 3.0 295 70 -15 3.33 0.5445
WVFGRD96 4.0 295 70 -15 3.35 0.5508
WVFGRD96 5.0 300 60 10 3.39 0.5529
WVFGRD96 6.0 300 60 10 3.40 0.5553
WVFGRD96 7.0 300 60 10 3.41 0.5554
WVFGRD96 8.0 300 55 10 3.44 0.5548
WVFGRD96 9.0 300 60 10 3.44 0.5512
WVFGRD96 10.0 300 60 10 3.45 0.5473
WVFGRD96 11.0 300 60 10 3.46 0.5426
WVFGRD96 12.0 300 60 10 3.47 0.5371
WVFGRD96 13.0 295 65 -10 3.47 0.5316
WVFGRD96 14.0 300 75 25 3.48 0.5261
WVFGRD96 15.0 300 75 25 3.48 0.5260
WVFGRD96 16.0 300 75 20 3.49 0.5249
WVFGRD96 17.0 300 75 20 3.50 0.5241
WVFGRD96 18.0 300 75 20 3.51 0.5222
WVFGRD96 19.0 300 75 20 3.52 0.5193
WVFGRD96 20.0 300 75 20 3.52 0.5156
WVFGRD96 21.0 300 75 20 3.53 0.5118
WVFGRD96 22.0 300 75 20 3.54 0.5074
WVFGRD96 23.0 300 75 20 3.55 0.5022
WVFGRD96 24.0 300 75 15 3.55 0.4965
WVFGRD96 25.0 300 75 15 3.56 0.4907
WVFGRD96 26.0 295 90 20 3.57 0.4848
WVFGRD96 27.0 295 90 20 3.57 0.4789
WVFGRD96 28.0 295 90 20 3.58 0.4729
WVFGRD96 29.0 295 90 20 3.59 0.4668
WVFGRD96 30.0 295 90 20 3.60 0.4606
WVFGRD96 31.0 295 90 20 3.60 0.4540
WVFGRD96 32.0 115 85 -20 3.61 0.4476
WVFGRD96 33.0 295 90 20 3.62 0.4405
WVFGRD96 34.0 115 85 -15 3.63 0.4340
WVFGRD96 35.0 115 85 -15 3.64 0.4266
WVFGRD96 36.0 295 90 15 3.65 0.4192
WVFGRD96 37.0 295 90 15 3.67 0.4118
WVFGRD96 38.0 295 90 15 3.68 0.4036
WVFGRD96 39.0 300 80 15 3.69 0.3953
WVFGRD96 40.0 300 75 20 3.72 0.3853
WVFGRD96 41.0 300 75 20 3.73 0.3789
WVFGRD96 42.0 300 75 20 3.74 0.3724
WVFGRD96 43.0 300 75 20 3.74 0.3665
WVFGRD96 44.0 300 75 20 3.75 0.3607
WVFGRD96 45.0 300 75 20 3.76 0.3549
WVFGRD96 46.0 300 75 20 3.76 0.3491
WVFGRD96 47.0 300 75 15 3.77 0.3433
WVFGRD96 48.0 300 75 15 3.77 0.3377
WVFGRD96 49.0 300 75 15 3.78 0.3322
WVFGRD96 50.0 300 75 15 3.78 0.3268
The best solution is
WVFGRD96 7.0 300 60 10 3.41 0.5554
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 0.06 n 3 br c 0.12 0.25 n 4 p 2 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 Oct 18 09:36:54 CDT 2008