The ANSS event ID is usp000ha1w and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000ha1w/executive.
2010/03/28 00:03:55 32.438 -104.501 4.0 4.1 NewMexico
USGS/SLU Moment Tensor Solution ENS 2010/03/28 00:03:55:0 32.44 -104.50 4.0 4.1 NewMexico Stations used: IM.TX31 IU.ANMO SC.Y22A TA.121A TA.128A TA.129A TA.131A TA.133A TA.228A TA.229A TA.231A TA.232A TA.329A TA.ABTX TA.MSTX TA.T25A TA.U23A TA.U24A TA.U25A TA.U26A TA.V23A TA.V24A TA.V25A TA.V26A TA.W24A TA.W25A TA.W26A TA.Y29A TA.Y30A TA.Y32A TA.Z28A TA.Z29A US.MNTX XR.SC05 XR.SC07 XR.SC08 XR.SC09 XR.SC10 XR.SC11 XR.SC12 XR.SC13 XR.SC15 XR.SC16 XR.SC19 XR.SC20 XR.SC21 XR.SC22 XR.SC23 XR.SC25 XR.SC26 XR.SC27 XR.SC29 XR.SC30 XR.SC31 XR.SC32 XR.SC33 XR.SC35 XR.SC36 XR.SC37 XR.SC38 XR.SC39 XR.SC41 XR.SC42 XR.SC43 XR.SC44 XR.SC45 XR.SC48 XR.SC49 XR.SC51 XR.SC53 XR.SC54 XR.SC57 XR.SC58 XR.SC60 XR.SC61 XR.SC62 XR.SC64 XR.SC67 XR.SC70 Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.17e+22 dyne-cm Mw = 3.98 Z = 4 km Plane Strike Dip Rake NP1 220 50 -85 NP2 32 40 -96 Principal Axes: Axis Value Plunge Azimuth T 1.17e+22 5 306 N 0.00e+00 4 37 P -1.17e+22 84 165 Moment Tensor: (dyne-cm) Component Value Mxx 3.99e+21 Mxy -5.54e+21 Mxz 1.81e+21 Myy 7.54e+21 Myz -1.13e+21 Mzz -1.15e+22 ############## ###################### #####################-----## ################-----------## T ############----------------### # ##########------------------#### #############--------------------##### ############----------------------###### ###########-----------------------###### ###########------------------------####### ##########-------------------------####### #########----------- -----------######## ########------------ P ----------######### ######------------- ----------######## ######-------------------------######### #####-----------------------########## ####----------------------########## ###--------------------########### #------------------########### #-------------############## ------################ ############## Global CMT Convention Moment Tensor: R T P -1.15e+22 1.81e+21 1.13e+21 1.81e+21 3.99e+21 5.54e+21 1.13e+21 5.54e+21 7.54e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100328000355/index.html |
STK = 220 DIP = 50 RAKE = -85 MW = 3.98 HS = 4.0
The NDK file is 20100328000355.ndk The waveform inversion is preferred.
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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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:
cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 240 50 -55 3.76 0.2922 WVFGRD96 2.0 235 50 -60 3.87 0.3760 WVFGRD96 3.0 230 50 -70 3.93 0.4132 WVFGRD96 4.0 220 50 -85 3.98 0.4175 WVFGRD96 5.0 220 45 -85 3.99 0.3891 WVFGRD96 6.0 235 50 -65 3.98 0.3502 WVFGRD96 7.0 260 90 20 3.91 0.3335 WVFGRD96 8.0 230 55 -70 4.03 0.3476 WVFGRD96 9.0 265 75 20 3.95 0.3390 WVFGRD96 10.0 265 75 25 3.97 0.3423 WVFGRD96 11.0 265 70 25 3.98 0.3453 WVFGRD96 12.0 265 70 25 3.99 0.3486 WVFGRD96 13.0 265 70 25 4.00 0.3508 WVFGRD96 14.0 265 70 25 4.01 0.3523 WVFGRD96 15.0 265 70 25 4.02 0.3533 WVFGRD96 16.0 265 70 30 4.02 0.3542 WVFGRD96 17.0 265 65 25 4.03 0.3547 WVFGRD96 18.0 265 70 30 4.04 0.3548 WVFGRD96 19.0 265 70 30 4.04 0.3547
The best solution is
WVFGRD96 4.0 220 50 -85 3.98 0.4175
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
cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3
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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