2011/04/13 22:10:08 38.371 118.748 13 4.40 Nevada
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/04/13 22:10:08:0 38.37 118.75 13.0 4.4 Nevada Stations used: BK.BRIB BK.BRK BK.CMB BK.GASB BK.HAST BK.HELL BK.HUMO BK.JCC BK.JRSC BK.MHC BK.MOD BK.ORV BK.SAO BK.SUTB BK.VAK BK.WDC BK.WENL BK.YBH CI.BEL CI.GSC CI.MLAC II.PFO LB.DAC NC.AFD NC.KHMB NC.MDPB US.ELK UU.BGU UU.CCUT UU.KNB UU.LCMT UU.PKCU UU.PSUT UU.SZCU UU.TCRU UW.TREE Filtering commands used: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 3.55e+22 dynecm Mw = 4.30 Z = 3 km Plane Strike Dip Rake NP1 358 45 95 NP2 185 45 85 Principal Axes: Axis Value Plunge Azimuth T 3.55e+22 0 91 N 0.00e+00 4 1 P 3.55e+22 86 183 Moment Tensor: (dynecm) Component Value Mxx 1.11e+20 Mxy 9.15e+20 Mxz 2.18e+21 Myy 3.55e+22 Myz 1.91e+20 Mzz 3.53e+22 ########### ############### ################# ################ ################## ################## ################## #################### ################## #################### ################## ########## ######## T ########## P ######## ######### ######### ################## ################## ################# ################ ############## ############### ########### ####### Global CMT Convention Moment Tensor: R T P 3.53e+22 2.18e+21 1.91e+20 2.18e+21 1.11e+20 9.15e+20 1.91e+20 9.15e+20 3.55e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110413221008/index.html 
STK = 185 DIP = 45 RAKE = 85 MW = 4.30 HS = 3.0
The NDK file is 20110413221008.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/04/13 22:10:08:0 38.37 118.75 13.0 4.4 Nevada Stations used: BK.BRIB BK.BRK BK.CMB BK.GASB BK.HAST BK.HELL BK.HUMO BK.JCC BK.JRSC BK.MHC BK.MOD BK.ORV BK.SAO BK.SUTB BK.VAK BK.WDC BK.WENL BK.YBH CI.BEL CI.GSC CI.MLAC II.PFO LB.DAC NC.AFD NC.KHMB NC.MDPB US.ELK UU.BGU UU.CCUT UU.KNB UU.LCMT UU.PKCU UU.PSUT UU.SZCU UU.TCRU UW.TREE Filtering commands used: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 3.55e+22 dynecm Mw = 4.30 Z = 3 km Plane Strike Dip Rake NP1 358 45 95 NP2 185 45 85 Principal Axes: Axis Value Plunge Azimuth T 3.55e+22 0 91 N 0.00e+00 4 1 P 3.55e+22 86 183 Moment Tensor: (dynecm) Component Value Mxx 1.11e+20 Mxy 9.15e+20 Mxz 2.18e+21 Myy 3.55e+22 Myz 1.91e+20 Mzz 3.53e+22 ########### ############### ################# ################ ################## ################## ################## #################### ################## #################### ################## ########## ######## T ########## P ######## ######### ######### ################## ################## ################# ################ ############## ############### ########### ####### Global CMT Convention Moment Tensor: R T P 3.53e+22 2.18e+21 1.91e+20 2.18e+21 1.11e+20 9.15e+20 1.91e+20 9.15e+20 3.55e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110413221008/index.html 
REVIEWED BY NSL STAFF Event ID:332872 Origin ID:788353 Algorithm: Ichinose (2003) Long Period, RegionalDistance Waves Seismic Moment Tensor Solution 2011/04/13 (103) 22:10:06.00 38.3715 118.7476 788353 Depth = 18.0 (km) Mw = 4.34 Mo = 4.06x10^22 (dyne x cm) Percent Double Couple = 98 % Percent CLVD = 2 % no ISO calculated Epsilon=0.01 Percent Variance Reduction = 45.58 % Total Fit = 14.78 Major Double Couple strike dip rake Nodal Plane 1: 66 23 29 Nodal Plane 2: 309 79 110 DEVIATORIC MOMENT TENSOR Moment Tensor Elements: Spherical Coordinates Mrr= 1.39 Mtt= 2.19 Mff= 0.80 Mrt= 2.60 Mrf= 2.42 Mtf= 0.43 EXP=22 Moment Tensor Elements: Cartesian Coordinates 2.19 0.43 2.60 0.43 0.80 2.42 2.60 2.42 1.39 Eigenvalues: Taxis eigenvalue= 4.04 Naxis eigenvalue= 0.04 Paxis eigenvalue= 4.08 Eigenvalues and eigenvectors of the Major Double Couple: Taxis ev= 4.04 trend=242 plunge=52 Naxis ev= 0.00 trend=125 plunge=20 Paxis ev=4.04 trend=23 plunge=31 Maximum Azmuithal Gap=216 Distance to Nearest Station=148.3 (km) Number of Stations (D=Displacement/V=Velocity) Used=5 (defining only) CMB.BK.D DAC.LB.D ORV.BK.D MHC.BK.D SAO.BK.D     P    #### ######## ############ ################# ###################### ######################## ########################### ############################# ################################ ################################## ####### ########################## ####### T ############################# ###### ############################## ######################################## ###################################### ################################ ####################### ###############   All Stations defining and nondefining: Station.Net Def Distance Azi Bazi lof hif vmodel (km) (deg) (deg) (Hz) (Hz) CMB.BK (D) Y 148.3 256 75 0.020 0.080 CMB.BK.wus.glib DAC.LB (D) Y 253.9 156 337 0.020 0.080 DAC.LB.wus.glib ORV.BK (D) Y 271.4 300 118 0.020 0.080 ORV.BK.wus.glib MHC.BK (D) Y 278.4 247 65 0.020 0.080 MHC.BK.wus.glib SAO.BK (D) Y 297.8 234 52 0.020 0.080 SAO.BK.wus.glib (V)velocity (D)Displacement Author: wwwdata Date: 2011/04/13 23:00:20 mtinv Version 2.1_DEVEL OCT2008 
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
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.

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 0.05 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 180 45 95 4.12 0.4474 WVFGRD96 1.0 185 45 85 4.16 0.4670 WVFGRD96 2.0 185 45 85 4.24 0.5352 WVFGRD96 3.0 185 45 85 4.30 0.5420 WVFGRD96 4.0 195 50 70 4.32 0.4858 WVFGRD96 5.0 210 70 55 4.31 0.4266 WVFGRD96 6.0 210 75 55 4.31 0.4147 WVFGRD96 7.0 50 70 25 4.28 0.4209 WVFGRD96 8.0 205 75 65 4.38 0.4459 WVFGRD96 9.0 205 75 65 4.38 0.4535 WVFGRD96 10.0 205 75 65 4.37 0.4617 WVFGRD96 11.0 205 75 65 4.37 0.4693 WVFGRD96 12.0 205 75 65 4.37 0.4751 WVFGRD96 13.0 205 75 65 4.37 0.4803 WVFGRD96 14.0 205 75 65 4.37 0.4834 WVFGRD96 15.0 210 80 60 4.37 0.4861 WVFGRD96 16.0 210 80 60 4.38 0.4875 WVFGRD96 17.0 50 70 40 4.40 0.4902 WVFGRD96 18.0 50 70 40 4.41 0.4935 WVFGRD96 19.0 50 70 40 4.41 0.4950 WVFGRD96 20.0 50 70 40 4.42 0.4951 WVFGRD96 21.0 55 65 40 4.42 0.4899 WVFGRD96 22.0 55 65 40 4.43 0.4875 WVFGRD96 23.0 55 65 40 4.43 0.4840 WVFGRD96 24.0 55 65 35 4.44 0.4797 WVFGRD96 25.0 55 65 35 4.45 0.4748 WVFGRD96 26.0 185 65 60 4.41 0.4690 WVFGRD96 27.0 185 65 60 4.41 0.4647 WVFGRD96 28.0 180 65 60 4.41 0.4600 WVFGRD96 29.0 175 60 65 4.41 0.4554
The best solution is
WVFGRD96 3.0 185 45 85 4.30 0.5420
The mechanism correspond to the best fit is

The best fit as a function of depth is given in the following figure:

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 observedpredicted 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 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 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 0.05 n 3

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. 
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 following figure shows the stations used in the grid search for the best focal mechanism to fit the surfacewave spectral amplitudes of the Love and Rayleigh waves.

The surfacewave determined focal mechanism is shown here.
NODAL PLANES STK= 179.99 DIP= 60.00 RAKE= 94.99 OR STK= 9.90 DIP= 30.38 RAKE= 81.43 DEPTH = 3.0 km Mw = 4.44 Best Fit 0.9087  PT axis plot gives solutions with FIT greater than FIT90
The Pwave first motion data for focal mechanism studies are as follow:
Sta Az Dist First motion
Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surfacewave radiation pattern search program srfgrd96.
Digital data were collected, instrument response removed and traces converted
to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh and Lovewave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.

Pressuretension axis trends. Since the surfacewave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and Taxes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. 
Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0180 degrees are sampled. 
The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used
Since the analysis of the surfacewave radiation patterns uses only spectral amplitudes and because the surfavewave radiation patterns have a 180 degree symmetry, each surfacewave solution consists of four possible focal mechanisms corresponding to the interchange of the P and Taxes and a roation of the mechanism by 180 degrees. To select one mechanism, Pwave first motion can be used. This was not possible in this case because all the Pwave first motions were emergent ( a feature of the Pwave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.
The fits to the waveforms with the given mechanism are show below:
This figure shows the fit to the three components of motion (Z  vertical, Rradial and T  transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:
hp c 0.02 n 3 lp c 0.05 n 3
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The WUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 Model after 8 iterations ISOTROPIC KGS FLAT EARTH 1D 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 0.302E02 0.679E02 0.00 0.00 1.00 1.00 6.1000 5.5445 3.2953 2.6089 0.349E02 0.784E02 0.00 0.00 1.00 1.00 13.0000 6.2708 3.7396 2.7812 0.212E02 0.476E02 0.00 0.00 1.00 1.00 19.0000 6.4075 3.7680 2.8223 0.111E02 0.249E02 0.00 0.00 1.00 1.00 0.0000 7.9000 4.6200 3.2760 0.164E10 0.370E10 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: