Location SLU
2009/09/14 18:27:23 36.5506 -106.4719 8.5 4.00 New Mexico
The program elocate was used with the WUS model to locate this event. The details are given int he 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
2009/09/14 18:27:23 36.551 -106.371 5.0 3.2 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 2009/09/14 18:27:23:0 36.55 -106.47 8.5 4.0 New Mexico
Stations used:
TA.Q21A TA.Q22A TA.R20A TA.R21A TA.R22A TA.S21A TA.S22A
TA.S24A TA.S25A TA.S26A TA.T21A TA.T22A TA.T23A TA.T24B
TA.T25A TA.T26A TA.U21A TA.U22A TA.U23A TA.U24A TA.V21A
TA.V23A TA.V24A TA.W24A
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 = 1.88e+21 dyne-cm
Mw = 3.45
Z = 12 km
Plane Strike Dip Rake
NP1 345 73 -148
NP2 245 60 -20
Principal Axes:
Axis Value Plunge Azimuth
T 1.88e+21 8 113
N 0.00e+00 54 11
P -1.88e+21 34 209
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.16e+20
Mxy -1.20e+21
Mxz 6.66e+20
Myy 1.27e+21
Myz 6.66e+20
Mzz -5.58e+20
##------------
########--------------
############----------------
##############----------------
#################-----------------
###################--------####-----
###################--#################
################-------#################
#############----------#################
###########--------------#################
#########----------------#################
#######-------------------################
#####---------------------################
###----------------------###############
##------------------------########## #
-------------------------########## T
---------- -----------##########
--------- P -----------###########
------- -----------#########
--------------------########
-----------------#####
------------##
Global CMT Convention Moment Tensor:
R T P
-5.58e+20 6.66e+20 -6.66e+20
6.66e+20 -7.16e+20 1.20e+21
-6.66e+20 1.20e+21 1.27e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090914182723/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 = 245
DIP = 60
RAKE = -20
MW = 3.45
HS = 12.0
Both the CUS and WUS models give similar fits. We use the WUS model since that model was used for the locaiton.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
SLUFM |
USGS/SLU Moment Tensor Solution
ENS 2009/09/14 18:27:23:0 36.55 -106.47 8.5 4.0 New Mexico
Stations used:
TA.Q21A TA.Q22A TA.R20A TA.R21A TA.R22A TA.S21A TA.S22A
TA.S24A TA.S25A TA.S26A TA.T21A TA.T22A TA.T23A TA.T24B
TA.T25A TA.T26A TA.U21A TA.U22A TA.U23A TA.U24A TA.V21A
TA.V23A TA.V24A TA.W24A
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 = 1.88e+21 dyne-cm
Mw = 3.45
Z = 12 km
Plane Strike Dip Rake
NP1 345 73 -148
NP2 245 60 -20
Principal Axes:
Axis Value Plunge Azimuth
T 1.88e+21 8 113
N 0.00e+00 54 11
P -1.88e+21 34 209
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.16e+20
Mxy -1.20e+21
Mxz 6.66e+20
Myy 1.27e+21
Myz 6.66e+20
Mzz -5.58e+20
##------------
########--------------
############----------------
##############----------------
#################-----------------
###################--------####-----
###################--#################
################-------#################
#############----------#################
###########--------------#################
#########----------------#################
#######-------------------################
#####---------------------################
###----------------------###############
##------------------------########## #
-------------------------########## T
---------- -----------##########
--------- P -----------###########
------- -----------#########
--------------------########
-----------------#####
------------##
Global CMT Convention Moment Tensor:
R T P
-5.58e+20 6.66e+20 -6.66e+20
6.66e+20 -7.16e+20 1.20e+21
-6.66e+20 1.20e+21 1.27e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090914182723/index.html
|
Plot of First Motions and Nodal Planes of Final Solution
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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 0.10 n 3
br c 0.12 0.25 n 4 p 2
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 195 45 -100 3.04 0.1931
WVFGRD96 1.0 75 85 0 2.99 0.2229
WVFGRD96 2.0 75 85 5 3.18 0.3749
WVFGRD96 3.0 75 80 10 3.24 0.4240
WVFGRD96 4.0 75 65 10 3.29 0.4522
WVFGRD96 5.0 250 60 -15 3.33 0.4744
WVFGRD96 6.0 250 60 -15 3.36 0.5014
WVFGRD96 7.0 250 60 -15 3.38 0.5190
WVFGRD96 8.0 245 50 -25 3.43 0.5312
WVFGRD96 9.0 245 55 -25 3.44 0.5409
WVFGRD96 10.0 245 55 -20 3.44 0.5448
WVFGRD96 11.0 245 60 -20 3.44 0.5467
WVFGRD96 12.0 245 60 -20 3.45 0.5469
WVFGRD96 13.0 250 65 -10 3.46 0.5457
WVFGRD96 14.0 245 65 -15 3.46 0.5437
WVFGRD96 15.0 245 65 -15 3.47 0.5412
WVFGRD96 16.0 245 65 -15 3.48 0.5378
WVFGRD96 17.0 245 65 -15 3.49 0.5335
WVFGRD96 18.0 245 65 -15 3.50 0.5285
WVFGRD96 19.0 245 65 -15 3.51 0.5226
WVFGRD96 20.0 245 65 -15 3.52 0.5164
WVFGRD96 21.0 245 65 -15 3.53 0.5097
WVFGRD96 22.0 245 65 -15 3.54 0.5019
WVFGRD96 23.0 245 65 -15 3.55 0.4936
WVFGRD96 24.0 245 65 -15 3.55 0.4852
WVFGRD96 25.0 245 70 -15 3.56 0.4772
WVFGRD96 26.0 245 70 -15 3.56 0.4696
WVFGRD96 27.0 245 70 -15 3.57 0.4617
WVFGRD96 28.0 245 70 -15 3.58 0.4543
WVFGRD96 29.0 245 70 -15 3.58 0.4470
The best solution is
WVFGRD96 12.0 245 60 -20 3.45 0.5469
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 0.10 n 3
br c 0.12 0.25 n 4 p 2
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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.
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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=Tue Sep 15 14:58:21 CDT 2009
Last Changed 2009/09/14