The ANSS event ID is usp000h1h9 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000h1h9/executive.
2009/09/14 18:27:23 36.545 -106.460 5.0 3.5 New Mexico
USGS/SLU Moment Tensor Solution ENS 2009/09/14 18:27:23:0 36.54 -106.46 5.0 3.5 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 |
STK = 245 DIP = 60 RAKE = -20 MW = 3.45 HS = 12.0
The NDK file is 20090914182723.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution ENS 2009/09/14 18:27:23:0 36.54 -106.46 5.0 3.5 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 |
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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 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 corresponding 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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
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. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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