2010/01/18 08:41:07 36.8500 -104.8700 5.0 4.00 New Mexico
After an initial inversion run, large time shifts were required. We picked arrivals form the permanent and the TA network for use with the elocate programs and the CUS model. The SLU location isabout 0.1 degree west of the initial NEIC location. I prefer the SLU location because the waveform time shifts are no longer as large as -4 seconds at short distances. Output of elocate
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/01/18 08:41:07:0 36.85 -104.87 5.0 4.0 New Mexico Stations used: IU.ANMO TA.KSCO TA.MSTX TA.P27A TA.P28A TA.Q23A TA.Q26A TA.Q28A TA.Q29A TA.R24A TA.R25A TA.R26A TA.R27A TA.S22A TA.S23A TA.S24A TA.S25A TA.S26A TA.S27A TA.T23A TA.T24B TA.T25A TA.T26A TA.U23A TA.U24A TA.U25A TA.U26A TA.U27A TA.U28A TA.V22A TA.V23A TA.V24A TA.V25A TA.V26A TA.V27A TA.V28A TA.V29A TA.W23A TA.W24A TA.W26A TA.W27A TA.W28A TA.W29A TA.W30A TA.X23A TA.X24A TA.X26A TA.X27A TA.X28A TA.X29A TA.Y24A TA.Z24A US.MVCO US.SDCO Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 7.24e+21 dyne-cm Mw = 3.84 Z = 5 km Plane Strike Dip Rake NP1 20 65 -45 NP2 133 50 -147 Principal Axes: Axis Value Plunge Azimuth T 7.24e+21 9 80 N 0.00e+00 40 177 P -7.24e+21 49 339 Moment Tensor: (dyne-cm) Component Value Mxx -2.53e+21 Mxy 2.30e+21 Mxz -3.16e+21 Myy 6.45e+21 Myz 2.35e+21 Mzz -3.92e+21 -------------- -------------------### ----------------------###### -----------------------####### #----------- -----------######## ##----------- P -----------######### ####---------- ----------########### #####-----------------------######### #####-----------------------######### T #######---------------------########## # ########--------------------############## #########------------------############### ##########-----------------############### ###########--------------############### ############------------################ #############---------################ ###############-----################ #################-################ ###############----########### ############---------------- #######--------------- -------------- Global CMT Convention Moment Tensor: R T P -3.92e+21 -3.16e+21 -2.35e+21 -3.16e+21 -2.53e+21 -2.30e+21 -2.35e+21 -2.30e+21 6.45e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100118084107/index.html |
STK = 20 DIP = 65 RAKE = -45 MW = 3.84 HS = 5.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/01/18 08:41:07:0 36.85 -104.87 5.0 4.0 New Mexico Stations used: IU.ANMO TA.KSCO TA.MSTX TA.P27A TA.P28A TA.Q23A TA.Q26A TA.Q28A TA.Q29A TA.R24A TA.R25A TA.R26A TA.R27A TA.S22A TA.S23A TA.S24A TA.S25A TA.S26A TA.S27A TA.T23A TA.T24B TA.T25A TA.T26A TA.U23A TA.U24A TA.U25A TA.U26A TA.U27A TA.U28A TA.V22A TA.V23A TA.V24A TA.V25A TA.V26A TA.V27A TA.V28A TA.V29A TA.W23A TA.W24A TA.W26A TA.W27A TA.W28A TA.W29A TA.W30A TA.X23A TA.X24A TA.X26A TA.X27A TA.X28A TA.X29A TA.Y24A TA.Z24A US.MVCO US.SDCO Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 7.24e+21 dyne-cm Mw = 3.84 Z = 5 km Plane Strike Dip Rake NP1 20 65 -45 NP2 133 50 -147 Principal Axes: Axis Value Plunge Azimuth T 7.24e+21 9 80 N 0.00e+00 40 177 P -7.24e+21 49 339 Moment Tensor: (dyne-cm) Component Value Mxx -2.53e+21 Mxy 2.30e+21 Mxz -3.16e+21 Myy 6.45e+21 Myz 2.35e+21 Mzz -3.92e+21 -------------- -------------------### ----------------------###### -----------------------####### #----------- -----------######## ##----------- P -----------######### ####---------- ----------########### #####-----------------------######### #####-----------------------######### T #######---------------------########## # ########--------------------############## #########------------------############### ##########-----------------############### ###########--------------############### ############------------################ #############---------################ ###############-----################ #################-################ ###############----########### ############---------------- #######--------------- -------------- Global CMT Convention Moment Tensor: R T P -3.92e+21 -3.16e+21 -2.35e+21 -3.16e+21 -2.53e+21 -2.30e+21 -2.35e+21 -2.30e+21 6.45e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100118084107/index.html |
First motion plot using elocate take-off angles and azimuths |
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 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 85 -55 3.84 0.3379 WVFGRD96 1.0 215 90 60 3.89 0.3453 WVFGRD96 2.0 30 80 -50 3.83 0.3752 WVFGRD96 3.0 25 70 -45 3.83 0.4005 WVFGRD96 4.0 20 65 -45 3.84 0.4191 WVFGRD96 5.0 20 65 -45 3.84 0.4248 WVFGRD96 6.0 25 70 -40 3.83 0.4246 WVFGRD96 7.0 25 70 -35 3.84 0.4223 WVFGRD96 8.0 30 75 -30 3.84 0.4168 WVFGRD96 9.0 30 80 -30 3.84 0.4123 WVFGRD96 10.0 30 80 -30 3.86 0.4060 WVFGRD96 11.0 30 80 -30 3.87 0.3983 WVFGRD96 12.0 30 80 -30 3.88 0.3906 WVFGRD96 13.0 30 80 -30 3.88 0.3822 WVFGRD96 14.0 30 85 -30 3.89 0.3729 WVFGRD96 15.0 30 80 -30 3.89 0.3641 WVFGRD96 16.0 30 80 -25 3.90 0.3552 WVFGRD96 17.0 215 80 25 3.91 0.3479 WVFGRD96 18.0 30 90 -25 3.91 0.3357 WVFGRD96 19.0 30 85 -25 3.92 0.3266 WVFGRD96 20.0 215 80 30 3.93 0.3204 WVFGRD96 21.0 215 80 30 3.94 0.3124 WVFGRD96 22.0 215 80 30 3.94 0.3046 WVFGRD96 23.0 30 90 -30 3.95 0.2951 WVFGRD96 24.0 30 90 -25 3.95 0.2885 WVFGRD96 25.0 30 85 -25 3.96 0.2831 WVFGRD96 26.0 215 80 25 3.96 0.2807 WVFGRD96 27.0 215 80 25 3.97 0.2762 WVFGRD96 28.0 215 80 25 3.97 0.2721 WVFGRD96 29.0 215 80 25 3.97 0.2687
The best solution is
WVFGRD96 5.0 20 65 -45 3.84 0.4248
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
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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 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=Wed Jan 20 05:45:45 CST 2010