Location SLU
2009/09/23 13:03:15 34.476 -107.900 6.0 3.30 New Mexico
The program elocate was used with the WUS model to locate this event. The details are given in the file
WUS.txt (The velocity model file is VEL.MOD and the phase arrival file with station coordinates is elocate.dat. We used the azimiths and take-off angles for thiis earthquake to plot the P-wve first-motion focal mechanism, using the preferred mechanism form the waveform inversion, which is plotted below for comparison.
Location NEIC
2009/09/23 13:03:15 34.465 -107.830 5.0 3.3 NEW MEXICO
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 2009/09/23 13:03:14:0 34.48 -107.90 6.0 3.3 New Mexico
Stations used:
IU.ANMO TA.125A TA.S22A TA.U23A TA.V20A TA.V21A TA.W18A
TA.W20A TA.W21A TA.W22A TA.X20A TA.X22A TA.Y20A TA.Y21A
TA.Y22A TA.Y22D TA.Y23A TA.Y24A TA.Y25A TA.Y26A TA.Z20A
TA.Z21A TA.Z22A TA.Z24A
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.82e+21 dyne-cm
Mw = 3.44
Z = 5 km
Plane Strike Dip Rake
NP1 5 60 -65
NP2 142 38 -126
Principal Axes:
Axis Value Plunge Azimuth
T 1.82e+21 12 77
N 0.00e+00 21 172
P -1.82e+21 65 321
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.05e+20
Mxy 5.32e+20
Mxz -4.55e+20
Myy 1.53e+21
Myz 7.88e+20
Mzz -1.43e+21
----------####
---------------#######
#------------------#########
#--------------------#########
##----------------------##########
###----------------------###########
####----------------------############
#####---------- ----------#########
#####---------- P ----------######### T
######---------- ----------######### #
######-----------------------#############
#######----------------------#############
########--------------------##############
########-------------------#############
#########------------------#############
#########----------------#############
##########-------------#############
###########-----------############
############-------###########
##############---###########
############----------
#######-------
Global CMT Convention Moment Tensor:
R T P
-1.43e+21 -4.55e+20 -7.88e+20
-4.55e+20 -1.05e+20 -5.32e+20
-7.88e+20 -5.32e+20 1.53e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090923130314/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 = 5
DIP = 60
RAKE = -65
MW = 3.44
HS = 5.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
SLUFM |
USGS/SLU Moment Tensor Solution
ENS 2009/09/23 13:03:14:0 34.48 -107.90 6.0 3.3 New Mexico
Stations used:
IU.ANMO TA.125A TA.S22A TA.U23A TA.V20A TA.V21A TA.W18A
TA.W20A TA.W21A TA.W22A TA.X20A TA.X22A TA.Y20A TA.Y21A
TA.Y22A TA.Y22D TA.Y23A TA.Y24A TA.Y25A TA.Y26A TA.Z20A
TA.Z21A TA.Z22A TA.Z24A
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.82e+21 dyne-cm
Mw = 3.44
Z = 5 km
Plane Strike Dip Rake
NP1 5 60 -65
NP2 142 38 -126
Principal Axes:
Axis Value Plunge Azimuth
T 1.82e+21 12 77
N 0.00e+00 21 172
P -1.82e+21 65 321
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.05e+20
Mxy 5.32e+20
Mxz -4.55e+20
Myy 1.53e+21
Myz 7.88e+20
Mzz -1.43e+21
----------####
---------------#######
#------------------#########
#--------------------#########
##----------------------##########
###----------------------###########
####----------------------############
#####---------- ----------#########
#####---------- P ----------######### T
######---------- ----------######### #
######-----------------------#############
#######----------------------#############
########--------------------##############
########-------------------#############
#########------------------#############
#########----------------#############
##########-------------#############
###########-----------############
############-------###########
##############---###########
############----------
#######-------
Global CMT Convention Moment Tensor:
R T P
-1.43e+21 -4.55e+20 -7.88e+20
-4.55e+20 -1.05e+20 -5.32e+20
-7.88e+20 -5.32e+20 1.53e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090923130314/index.html
|
Plot of First Motions and Nodal Planes of Final Solution
|
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 0.05 n 3
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 15 55 -40 3.19 0.3164
WVFGRD96 1.0 15 55 -45 3.22 0.3256
WVFGRD96 2.0 15 60 -45 3.31 0.3955
WVFGRD96 3.0 10 60 -55 3.38 0.4325
WVFGRD96 4.0 10 65 -60 3.42 0.4607
WVFGRD96 5.0 5 60 -65 3.44 0.4750
WVFGRD96 6.0 5 55 -60 3.44 0.4719
WVFGRD96 7.0 5 55 -60 3.45 0.4552
WVFGRD96 8.0 0 55 -70 3.50 0.4699
WVFGRD96 9.0 10 60 -55 3.47 0.4380
WVFGRD96 10.0 20 70 -40 3.43 0.4094
WVFGRD96 11.0 25 75 -35 3.42 0.3941
WVFGRD96 12.0 210 90 25 3.41 0.3821
WVFGRD96 13.0 210 85 25 3.42 0.3741
WVFGRD96 14.0 210 80 25 3.42 0.3661
WVFGRD96 15.0 210 80 25 3.43 0.3590
WVFGRD96 16.0 210 75 20 3.43 0.3525
WVFGRD96 17.0 210 75 20 3.44 0.3477
WVFGRD96 18.0 210 75 20 3.44 0.3426
WVFGRD96 19.0 210 75 20 3.45 0.3378
WVFGRD96 20.0 210 80 20 3.45 0.3338
WVFGRD96 21.0 210 80 20 3.45 0.3294
WVFGRD96 22.0 210 80 15 3.46 0.3262
WVFGRD96 23.0 210 80 15 3.47 0.3229
WVFGRD96 24.0 210 80 15 3.47 0.3196
WVFGRD96 25.0 210 80 15 3.48 0.3163
WVFGRD96 26.0 210 80 15 3.48 0.3132
WVFGRD96 27.0 210 80 15 3.49 0.3101
WVFGRD96 28.0 210 80 15 3.49 0.3068
WVFGRD96 29.0 210 80 15 3.50 0.3035
The best solution is
WVFGRD96 5.0 5 60 -65 3.44 0.4750
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 0.05 n 3
|
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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.
|
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=Wed Sep 23 13:23:11 CDT 2009
Last Changed 2009/09/23