The ANSS event ID is ci37299263 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ci37299263/executive.
2016/01/24 15:32:16 34.697 -116.239 2.6 4.11 California
USGS/SLU Moment Tensor Solution ENS 2016/01/24 15:32:16:0 34.70 -116.24 2.6 4.1 California Stations used: AE.W13A AZ.FRD AZ.PFO AZ.RRSP AZ.SMER AZ.SND CI.ADO CI.BAR CI.BBR CI.BC3 CI.BEL CI.BFS CI.CCC CI.CGO CI.CHF CI.CWC CI.DAN CI.DEC CI.DGR CI.DJJ CI.EDW2 CI.FOX2 CI.FUR CI.GLA CI.GMR CI.GRA CI.GSC CI.HEC CI.ISA CI.LMR2 CI.LPC CI.MOP CI.MPM CI.MTP CI.MUR CI.MWC CI.NEE2 CI.OSI CI.PASC CI.PMD CI.RRX CI.RVR CI.SHO CI.SLA CI.SPG2 CI.TIN CI.TUQ CI.USC CI.VCS CI.VTV CI.WCS2 NN.LCH NN.SHP NN.V12A PY.BPH01 PY.BPH10 YN.GVAR1 YN.JF00 YN.RHIL YN.TR01 Filtering commands used: cut o DIST/3.3 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 1.10e+22 dyne-cm Mw = 3.96 Z = 11 km Plane Strike Dip Rake NP1 151 72 154 NP2 250 65 20 Principal Axes: Axis Value Plunge Azimuth T 1.10e+22 31 109 N 0.00e+00 58 299 P -1.10e+22 5 202 Moment Tensor: (dyne-cm) Component Value Mxx -8.54e+21 Mxy -6.23e+21 Mxz -7.76e+20 Myy 5.67e+21 Myz 4.92e+21 Mzz 2.87e+21 -------------- #--------------------- ####------------------------ #####------------------------- #######--------------------------- #########--------------------------- ##########-----------------#######---- ############-------##################### #############--######################### ############---########################### #########------########################### #######---------########################## #####------------################ ###### ##---------------############### T ##### #------------------############# ##### -------------------################### -------------------################# --------------------############## -------------------########### ----- ------------######## -- P ---------------## ------------- Global CMT Convention Moment Tensor: R T P 2.87e+21 -7.76e+20 -4.92e+21 -7.76e+20 -8.54e+21 6.23e+21 -4.92e+21 6.23e+21 5.67e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160124153216/index.html |
STK = 250 DIP = 65 RAKE = 20 MW = 3.96 HS = 11.0
The NDK file is 20160124153216.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 2016/01/24 15:32:16:0 34.70 -116.24 2.6 4.1 California Stations used: AE.W13A AZ.FRD AZ.PFO AZ.RRSP AZ.SMER AZ.SND CI.ADO CI.BAR CI.BBR CI.BC3 CI.BEL CI.BFS CI.CCC CI.CGO CI.CHF CI.CWC CI.DAN CI.DEC CI.DGR CI.DJJ CI.EDW2 CI.FOX2 CI.FUR CI.GLA CI.GMR CI.GRA CI.GSC CI.HEC CI.ISA CI.LMR2 CI.LPC CI.MOP CI.MPM CI.MTP CI.MUR CI.MWC CI.NEE2 CI.OSI CI.PASC CI.PMD CI.RRX CI.RVR CI.SHO CI.SLA CI.SPG2 CI.TIN CI.TUQ CI.USC CI.VCS CI.VTV CI.WCS2 NN.LCH NN.SHP NN.V12A PY.BPH01 PY.BPH10 YN.GVAR1 YN.JF00 YN.RHIL YN.TR01 Filtering commands used: cut o DIST/3.3 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 1.10e+22 dyne-cm Mw = 3.96 Z = 11 km Plane Strike Dip Rake NP1 151 72 154 NP2 250 65 20 Principal Axes: Axis Value Plunge Azimuth T 1.10e+22 31 109 N 0.00e+00 58 299 P -1.10e+22 5 202 Moment Tensor: (dyne-cm) Component Value Mxx -8.54e+21 Mxy -6.23e+21 Mxz -7.76e+20 Myy 5.67e+21 Myz 4.92e+21 Mzz 2.87e+21 -------------- #--------------------- ####------------------------ #####------------------------- #######--------------------------- #########--------------------------- ##########-----------------#######---- ############-------##################### #############--######################### ############---########################### #########------########################### #######---------########################## #####------------################ ###### ##---------------############### T ##### #------------------############# ##### -------------------################### -------------------################# --------------------############## -------------------########### ----- ------------######## -- P ---------------## ------------- Global CMT Convention Moment Tensor: R T P 2.87e+21 -7.76e+20 -4.92e+21 -7.76e+20 -8.54e+21 6.23e+21 -4.92e+21 6.23e+21 5.67e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160124153216/index.html |
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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 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 55 60 -40 3.63 0.3463 WVFGRD96 2.0 50 50 -45 3.78 0.4630 WVFGRD96 3.0 40 45 -60 3.87 0.5241 WVFGRD96 4.0 40 45 -60 3.90 0.5568 WVFGRD96 5.0 40 45 -60 3.92 0.5676 WVFGRD96 6.0 55 55 -35 3.88 0.5630 WVFGRD96 7.0 65 70 -15 3.87 0.5648 WVFGRD96 8.0 55 55 -35 3.94 0.5796 WVFGRD96 9.0 250 65 20 3.93 0.5781 WVFGRD96 10.0 250 65 20 3.94 0.5834 WVFGRD96 11.0 250 65 20 3.96 0.5844 WVFGRD96 12.0 250 65 20 3.97 0.5822 WVFGRD96 13.0 250 70 20 3.98 0.5781 WVFGRD96 14.0 250 70 20 3.99 0.5717 WVFGRD96 15.0 250 70 20 4.00 0.5645 WVFGRD96 16.0 250 70 20 4.01 0.5558 WVFGRD96 17.0 250 70 20 4.02 0.5466 WVFGRD96 18.0 250 70 20 4.03 0.5364 WVFGRD96 19.0 250 70 20 4.03 0.5258 WVFGRD96 20.0 250 70 20 4.04 0.5150 WVFGRD96 21.0 250 70 20 4.05 0.5039 WVFGRD96 22.0 250 70 20 4.06 0.4927 WVFGRD96 23.0 250 70 20 4.06 0.4813 WVFGRD96 24.0 250 70 20 4.07 0.4704 WVFGRD96 25.0 250 70 20 4.08 0.4593 WVFGRD96 26.0 250 70 20 4.08 0.4482 WVFGRD96 27.0 250 70 20 4.09 0.4374 WVFGRD96 28.0 250 70 20 4.09 0.4264 WVFGRD96 29.0 250 70 20 4.10 0.4162
The best solution is
WVFGRD96 11.0 250 65 20 3.96 0.5844
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 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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