2009/07/29 10:00:36 36.821 -104.797 5.0 3.80 New Mexico
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/07/29 10:00:36:0 36.82 -104.80 5.0 3.8 New Mexico
Stations used:
IU.ANMO IW.SMCO TA.MSTX TA.O22A TA.O23A TA.O24A TA.P22A
TA.P23A TA.P24A TA.P25A TA.Q20A TA.Q22A TA.Q23A TA.Q24A
TA.Q25A TA.R20A TA.R21A TA.R22A TA.R25A TA.S20A TA.S21A
TA.S22A TA.S23A TA.S24A TA.S25A TA.T21A TA.T22A TA.T23A
TA.T25A TA.U21A TA.U22A TA.U23A TA.U24A TA.U25A TA.U26A
TA.V21A TA.V22A TA.V24A TA.V25A TA.V26A TA.W20A TA.W21A
TA.W23A TA.W24A TA.W25A TA.W26A TA.W27A TA.X21A TA.X26A
TA.X27A TA.Y22A TA.Y23A TA.Y24A TA.Y25A TA.Y26A TA.Y27A
TA.Z22A TA.Z25A TA.Z26A US.AMTX US.ISCO US.MVCO US.SDCO
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.45e+22 dyne-cm
Mw = 4.04
Z = 4 km
Plane Strike Dip Rake
NP1 15 65 -65
NP2 147 35 -132
Principal Axes:
Axis Value Plunge Azimuth
T 1.45e+22 16 87
N 0.00e+00 23 184
P -1.45e+22 62 324
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.10e+21
Mxy 2.29e+21
Mxz -4.67e+21
Myy 1.21e+22
Myz 7.47e+21
Mzz -1.00e+22
-------------#
-----------------#####
##-------------------#######
##--------------------########
###----------------------#########
###-----------------------##########
####--------- -----------###########
#####--------- P -----------############
#####--------- ----------#############
######----------------------######### ##
######----------------------######### T ##
#######--------------------########## ##
#######--------------------###############
#######------------------###############
########-----------------###############
########---------------###############
#########------------###############
#########----------###############
##########------##############
############-###############
#########-----########
###-----------
Global CMT Convention Moment Tensor:
R T P
-1.00e+22 -4.67e+21 -7.47e+21
-4.67e+21 -2.10e+21 -2.29e+21
-7.47e+21 -2.29e+21 1.21e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090729100036/index.html
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STK = 15
DIP = 65
RAKE = -65
MW = 4.04
HS = 4.0
The waveform inversion is preferred. This was hard because the location straddles the CUS and WUS regions. The CUS gave the best fit at a shallow depth in the 0.02 - 0.06 Hz band. the fits in the normal 0.02 - 0.10 Hz band were slightly poorer but were deeper, e.g., about 10km with the smae mechanism. The event generated great Rayleigh waves in the 2 - 40 second period range - which I took ats an indication of shallow depth. The surface-wave technique had no real depth control, but the radiation patterns are better fit in RMS amplitude at the 2 km depth than at the 8 km depth.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/07/29 10:00:36:0 36.82 -104.80 5.0 3.8 New Mexico
Stations used:
IU.ANMO IW.SMCO TA.MSTX TA.O22A TA.O23A TA.O24A TA.P22A
TA.P23A TA.P24A TA.P25A TA.Q20A TA.Q22A TA.Q23A TA.Q24A
TA.Q25A TA.R20A TA.R21A TA.R22A TA.R25A TA.S20A TA.S21A
TA.S22A TA.S23A TA.S24A TA.S25A TA.T21A TA.T22A TA.T23A
TA.T25A TA.U21A TA.U22A TA.U23A TA.U24A TA.U25A TA.U26A
TA.V21A TA.V22A TA.V24A TA.V25A TA.V26A TA.W20A TA.W21A
TA.W23A TA.W24A TA.W25A TA.W26A TA.W27A TA.X21A TA.X26A
TA.X27A TA.Y22A TA.Y23A TA.Y24A TA.Y25A TA.Y26A TA.Y27A
TA.Z22A TA.Z25A TA.Z26A US.AMTX US.ISCO US.MVCO US.SDCO
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.45e+22 dyne-cm
Mw = 4.04
Z = 4 km
Plane Strike Dip Rake
NP1 15 65 -65
NP2 147 35 -132
Principal Axes:
Axis Value Plunge Azimuth
T 1.45e+22 16 87
N 0.00e+00 23 184
P -1.45e+22 62 324
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.10e+21
Mxy 2.29e+21
Mxz -4.67e+21
Myy 1.21e+22
Myz 7.47e+21
Mzz -1.00e+22
-------------#
-----------------#####
##-------------------#######
##--------------------########
###----------------------#########
###-----------------------##########
####--------- -----------###########
#####--------- P -----------############
#####--------- ----------#############
######----------------------######### ##
######----------------------######### T ##
#######--------------------########## ##
#######--------------------###############
#######------------------###############
########-----------------###############
########---------------###############
#########------------###############
#########----------###############
##########------##############
############-###############
#########-----########
###-----------
Global CMT Convention Moment Tensor:
R T P
-1.00e+22 -4.67e+21 -7.47e+21
-4.67e+21 -2.10e+21 -2.29e+21
-7.47e+21 -2.29e+21 1.21e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090729100036/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 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 30 80 -70 4.09 0.5867
WVFGRD96 1.0 25 75 -65 4.05 0.6036
WVFGRD96 2.0 20 70 -65 4.04 0.6403
WVFGRD96 3.0 15 65 -65 4.04 0.6578
WVFGRD96 4.0 15 65 -65 4.04 0.6608
WVFGRD96 5.0 10 60 -70 4.05 0.6503
WVFGRD96 6.0 10 60 -70 4.04 0.6300
WVFGRD96 7.0 10 60 -70 4.03 0.6061
WVFGRD96 8.0 30 80 -40 3.96 0.5872
WVFGRD96 9.0 30 80 -40 3.96 0.5824
WVFGRD96 10.0 30 80 -40 3.98 0.5824
WVFGRD96 11.0 35 90 -35 3.98 0.5771
WVFGRD96 12.0 35 90 -35 3.98 0.5736
WVFGRD96 13.0 220 80 35 3.99 0.5699
WVFGRD96 14.0 220 80 35 3.99 0.5664
WVFGRD96 15.0 220 80 35 3.99 0.5624
WVFGRD96 16.0 225 75 35 4.00 0.5578
WVFGRD96 17.0 225 75 35 4.00 0.5530
WVFGRD96 18.0 225 75 35 4.01 0.5479
WVFGRD96 19.0 225 75 35 4.01 0.5428
WVFGRD96 20.0 225 75 35 4.03 0.5349
WVFGRD96 21.0 40 70 30 4.03 0.5272
WVFGRD96 22.0 40 70 25 4.04 0.5218
WVFGRD96 23.0 35 80 -30 4.04 0.5176
WVFGRD96 24.0 35 80 -30 4.05 0.5118
WVFGRD96 25.0 35 80 -30 4.05 0.5056
WVFGRD96 26.0 30 75 -30 4.06 0.4986
WVFGRD96 27.0 30 75 -30 4.06 0.4916
WVFGRD96 28.0 30 75 -30 4.07 0.4844
WVFGRD96 29.0 30 75 -30 4.07 0.4770
The best solution is
WVFGRD96 4.0 15 65 -65 4.04 0.6608
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
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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. |
The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES
STK= 21.13
DIP= 71.25
RAKE= -54.00
OR
STK= 135.00
DIP= 40.00
RAKE= -149.99
DEPTH = 2.0 km
Mw = 4.08
Best Fit 0.8218 - P-T axis plot gives solutions with FIT greater than FIT90
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The P-wave first motion data for focal mechanism studies are as follow:
Sta Az Dist First motion
Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.
Digital data were collected, instrument response removed and traces converted
to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh- and Love-wave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.
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| Pressure-tension axis trends. Since the surface-wave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. |
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled. |
The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used
Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.
The fits to the waveforms with the given mechanism are show below:
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This figure shows the fit to the three components of motion (Z - vertical, R-radial and T - transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:
hp c 0.02 n 3 lp c 0.10 n 3
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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 CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 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=Thu Jul 30 19:33:51 CDT 2009
