The ANSS event ID is nn00502072 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00502072/executive.
2015/07/16 01:57:26 41.856 -119.654 9.4 3.2 Nevada
USGS/SLU Moment Tensor Solution ENS 2015/07/16 01:57:26:0 41.86 -119.65 9.4 3.2 Nevada Stations used: BK.WDC IM.NV31 IU.COR IW.MFID LB.TPH NC.AFD NC.KEB NC.KHMB NC.KRMB NN.BEK NN.KVN NN.LHV NN.PAH NN.PNT NN.REDF NN.RUB NN.RYN NN.SPR3 NN.VCN NN.WAK NN.YER TA.R11A UO.BUCK UO.PINE US.ELK US.HLID US.WVOR UW.BLOW UW.IRON UW.IZEE UW.TREE Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.55e+22 dyne-cm Mw = 4.06 Z = 9 km Plane Strike Dip Rake NP1 25 60 -75 NP2 177 33 -114 Principal Axes: Axis Value Plunge Azimuth T 1.55e+22 14 104 N 0.00e+00 13 197 P -1.55e+22 71 329 Moment Tensor: (dyne-cm) Component Value Mxx -3.45e+20 Mxy -2.73e+21 Mxz -4.98e+21 Myy 1.33e+22 Myz 5.93e+21 Mzz -1.30e+22 ###----------- #####---------------## ######------------------#### #####--------------------##### ######---------------------####### ######----------------------######## ######-----------------------######### #######--------- -----------########## ######---------- P -----------########## #######---------- ----------############ #######-----------------------############ #######----------------------############# #######---------------------######### ## #######-------------------########## T # #######------------------########### # #######----------------############### #######--------------############### #######-----------################ ######--------################ #######----################# #####-################ -----######### Global CMT Convention Moment Tensor: R T P -1.30e+22 -4.98e+21 -5.93e+21 -4.98e+21 -3.45e+20 2.73e+21 -5.93e+21 2.73e+21 1.33e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150716015726/index.html |
STK = 25 DIP = 60 RAKE = -75 MW = 4.06 HS = 9.0
The NDK file is 20150716015726.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 2015/07/16 01:57:26:0 41.86 -119.65 9.4 3.2 Nevada Stations used: BK.WDC IM.NV31 IU.COR IW.MFID LB.TPH NC.AFD NC.KEB NC.KHMB NC.KRMB NN.BEK NN.KVN NN.LHV NN.PAH NN.PNT NN.REDF NN.RUB NN.RYN NN.SPR3 NN.VCN NN.WAK NN.YER TA.R11A UO.BUCK UO.PINE US.ELK US.HLID US.WVOR UW.BLOW UW.IRON UW.IZEE UW.TREE Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.55e+22 dyne-cm Mw = 4.06 Z = 9 km Plane Strike Dip Rake NP1 25 60 -75 NP2 177 33 -114 Principal Axes: Axis Value Plunge Azimuth T 1.55e+22 14 104 N 0.00e+00 13 197 P -1.55e+22 71 329 Moment Tensor: (dyne-cm) Component Value Mxx -3.45e+20 Mxy -2.73e+21 Mxz -4.98e+21 Myy 1.33e+22 Myz 5.93e+21 Mzz -1.30e+22 ###----------- #####---------------## ######------------------#### #####--------------------##### ######---------------------####### ######----------------------######## ######-----------------------######### #######--------- -----------########## ######---------- P -----------########## #######---------- ----------############ #######-----------------------############ #######----------------------############# #######---------------------######### ## #######-------------------########## T # #######------------------########### # #######----------------############### #######--------------############### #######-----------################ ######--------################ #######----################# #####-################ -----######### Global CMT Convention Moment Tensor: R T P -1.30e+22 -4.98e+21 -5.93e+21 -4.98e+21 -3.45e+20 2.73e+21 -5.93e+21 2.73e+21 1.33e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150716015726/index.html |
Regional Moment Tensor (Mwr) Moment 1.200e+15 N-m Magnitude 3.99 Depth 8.0 km Percent DC 53% Half Duration – Catalog US (us20002xtz) Data Source US2 Contributor US2 Nodal Planes Plane Strike Dip Rake NP1 26 74 -74 NP2 162 22 -132 Principal Axes Axis Value Plunge Azimuth T 1.325 27 104 N -0.311 15 202 P -1.014 59 318 |
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:
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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 1.0 245 70 -20 3.73 0.4829 WVFGRD96 2.0 45 55 -40 3.87 0.5949 WVFGRD96 3.0 45 70 -55 3.93 0.6131 WVFGRD96 4.0 40 80 -70 4.03 0.6683 WVFGRD96 5.0 30 70 -75 4.03 0.7139 WVFGRD96 6.0 25 65 -75 4.03 0.7458 WVFGRD96 7.0 25 60 -75 4.03 0.7636 WVFGRD96 8.0 25 65 -75 4.07 0.7747 WVFGRD96 9.0 25 60 -75 4.06 0.7781 WVFGRD96 10.0 30 60 -70 4.05 0.7667 WVFGRD96 11.0 30 60 -65 4.03 0.7510 WVFGRD96 12.0 245 70 40 4.00 0.7352 WVFGRD96 13.0 245 70 40 4.01 0.7321 WVFGRD96 14.0 245 70 40 4.01 0.7255 WVFGRD96 15.0 245 70 35 4.01 0.7177 WVFGRD96 16.0 245 70 35 4.02 0.7084 WVFGRD96 17.0 245 70 35 4.02 0.6977 WVFGRD96 18.0 245 70 35 4.03 0.6862 WVFGRD96 19.0 245 70 35 4.03 0.6739 WVFGRD96 20.0 245 70 35 4.04 0.6611 WVFGRD96 21.0 245 75 35 4.05 0.6485 WVFGRD96 22.0 245 75 35 4.05 0.6353 WVFGRD96 23.0 245 75 35 4.06 0.6219 WVFGRD96 24.0 245 75 35 4.06 0.6091 WVFGRD96 25.0 245 75 35 4.07 0.5959 WVFGRD96 26.0 245 75 35 4.08 0.5830 WVFGRD96 27.0 245 75 35 4.08 0.5700 WVFGRD96 28.0 245 80 35 4.09 0.5568 WVFGRD96 29.0 245 80 35 4.10 0.5445
The best solution is
WVFGRD96 9.0 25 60 -75 4.06 0.7781
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 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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 CUS.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 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