2009/05/01 01:33:58 36.8510 -104.7840 5.0 3.50 New Mexico
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/05/01 01:33:58:0 36.85 -104.78 5.0 3.5 New Mexico
Stations used:
IU.ANMO TA.Q25A TA.R25A TA.S25A TA.T21A TA.T22A TA.T23A
TA.T24A TA.T25A TA.U21A TA.U24A TA.U25A TA.U26A TA.V24A
TA.V25A TA.W23A TA.W24A TA.X23A TA.X24A TA.X25A TA.X26A
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 = 6.24e+20 dyne-cm
Mw = 3.13
Z = 8 km
Plane Strike Dip Rake
NP1 185 85 20
NP2 93 70 175
Principal Axes:
Axis Value Plunge Azimuth
T 6.24e+20 18 51
N 0.00e+00 69 198
P -6.24e+20 10 317
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.02e+20
Mxy 5.78e+20
Mxz 3.26e+19
Myy 6.46e+19
Myz 2.14e+20
Mzz 3.70e+19
--------######
------------##########
------------#############
- P -----------###############
--- -----------############ ##
------------------############ T ###
-------------------############ ####
-------------------#####################
-------------------#####################
--------------------######################
#-------------------######################
###-----------------######################
########-----------####################---
###############---############----------
##################----------------------
#################---------------------
################--------------------
###############-------------------
#############-----------------
############----------------
#########-------------
#####---------
Global CMT Convention Moment Tensor:
R T P
3.70e+19 3.26e+19 -2.14e+20
3.26e+19 -1.02e+20 -5.78e+20
-2.14e+20 -5.78e+20 6.46e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090501013358/index.html
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STK = 185
DIP = 85
RAKE = 20
MW = 3.13
HS = 8.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/05/01 01:33:58:0 36.85 -104.78 5.0 3.5 New Mexico
Stations used:
IU.ANMO TA.Q25A TA.R25A TA.S25A TA.T21A TA.T22A TA.T23A
TA.T24A TA.T25A TA.U21A TA.U24A TA.U25A TA.U26A TA.V24A
TA.V25A TA.W23A TA.W24A TA.X23A TA.X24A TA.X25A TA.X26A
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 = 6.24e+20 dyne-cm
Mw = 3.13
Z = 8 km
Plane Strike Dip Rake
NP1 185 85 20
NP2 93 70 175
Principal Axes:
Axis Value Plunge Azimuth
T 6.24e+20 18 51
N 0.00e+00 69 198
P -6.24e+20 10 317
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.02e+20
Mxy 5.78e+20
Mxz 3.26e+19
Myy 6.46e+19
Myz 2.14e+20
Mzz 3.70e+19
--------######
------------##########
------------#############
- P -----------###############
--- -----------############ ##
------------------############ T ###
-------------------############ ####
-------------------#####################
-------------------#####################
--------------------######################
#-------------------######################
###-----------------######################
########-----------####################---
###############---############----------
##################----------------------
#################---------------------
################--------------------
###############-------------------
#############-----------------
############----------------
#########-------------
#####---------
Global CMT Convention Moment Tensor:
R T P
3.70e+19 3.26e+19 -2.14e+20
3.26e+19 -1.02e+20 -5.78e+20
-2.14e+20 -5.78e+20 6.46e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090501013358/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 0.5 180 80 -5 2.70 0.2291
WVFGRD96 1.0 180 85 0 2.75 0.2649
WVFGRD96 2.0 185 85 0 2.91 0.4318
WVFGRD96 3.0 185 80 0 2.98 0.4905
WVFGRD96 4.0 185 80 0 3.02 0.5261
WVFGRD96 5.0 185 75 0 3.05 0.5492
WVFGRD96 6.0 185 85 20 3.08 0.5629
WVFGRD96 7.0 185 85 15 3.10 0.5704
WVFGRD96 8.0 185 85 20 3.13 0.5740
WVFGRD96 9.0 185 85 20 3.14 0.5716
WVFGRD96 10.0 185 85 20 3.16 0.5665
WVFGRD96 11.0 185 85 20 3.17 0.5604
WVFGRD96 12.0 185 85 20 3.18 0.5536
WVFGRD96 13.0 185 85 20 3.19 0.5467
WVFGRD96 14.0 185 85 20 3.19 0.5398
WVFGRD96 15.0 185 85 15 3.20 0.5343
WVFGRD96 16.0 185 65 -15 3.22 0.5340
WVFGRD96 17.0 185 65 -20 3.23 0.5314
WVFGRD96 18.0 185 65 -15 3.24 0.5298
WVFGRD96 19.0 185 65 -15 3.25 0.5282
WVFGRD96 20.0 185 65 -15 3.26 0.5270
WVFGRD96 21.0 185 65 -15 3.27 0.5259
WVFGRD96 22.0 185 65 -15 3.28 0.5250
WVFGRD96 23.0 185 65 -15 3.29 0.5244
WVFGRD96 24.0 185 65 -10 3.30 0.5231
WVFGRD96 25.0 185 70 -5 3.30 0.5218
WVFGRD96 26.0 185 70 -5 3.31 0.5201
WVFGRD96 27.0 185 70 -5 3.32 0.5174
WVFGRD96 28.0 185 70 -5 3.33 0.5140
WVFGRD96 29.0 185 70 -5 3.33 0.5095
The best solution is
WVFGRD96 8.0 185 85 20 3.13 0.5740
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=Fri May 1 09:59:39 CDT 2009