Location

Location ANSS

The ANSS event ID is nn00570710 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00570710/executive.

2016/12/28 08:22:12 38.390 -118.897 12.2 5.6 Nevada

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2016/12/28 08:22:12:0 38.39 -118.90 12.2 5.6 Nevada Stations used: BK.SAO CI.GSC CI.ISA LB.BMN LB.TPH NC.AFD NC.BBGB NC.KCPB NC.MDPB NC.PMPB NN.BEK NN.CMK6 NN.COLR NN.DSP NN.EMB NN.GWY NN.KVN NN.LCH NN.MPK NN.MZPB NN.OMMB NN.PIO NN.PLTX NN.PNT NN.PRN NN.Q09A NN.REDF NN.S11A NN.VCN NN.WLDB NN.WTNK NN.YER SN.HEL TA.R11A US.ELK US.TPNV Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 2.16e+24 dyne-cm Mw = 5.49 Z = 13 km Plane Strike Dip Rake NP1 210 75 -20 NP2 305 71 -164 Principal Axes: Axis Value Plunge Azimuth T 2.16e+24 3 258 N 0.00e+00 65 355 P -2.16e+24 25 167 Moment Tensor: (dyne-cm) Component Value Mxx -1.61e+24 Mxy 8.21e+23 Mxz 7.76e+23 Myy 1.98e+24 Myz -2.92e+23 Mzz -3.70e+23 -------------- ---------------------# ---------------------####### --------------------########## ---------------------############# ##########----------################ ###############-----################## ###################-#################### ##################----################## ##################--------################ #################-----------############## ################--------------############ ############-----------------########## T ###########-------------------######## ###########---------------------###### ###########-----------------------#### #########-------------------------## ########-------------------------- #####------------ ---------- ####------------ P --------- #------------ ------ -------------- Global CMT Convention Moment Tensor: R T P -3.70e+23 7.76e+23 2.92e+23 7.76e+23 -1.61e+24 -8.21e+23 2.92e+23 -8.21e+23 1.98e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20161228082212/index.html

Preferred Solution

      STK = 210
      DIP = 75
     RAKE = -20
       MW = 5.49
       HS = 13.0

The NDK file is 20161228082212.ndk The waveform inversion is preferred.

Moment Tensor Comparison

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.

SLU	USGSMT	GCMT
USGS/SLU Moment Tensor Solution ENS 2016/12/28 08:22:12:0 38.39 -118.90 12.2 5.6 Nevada Stations used: BK.SAO CI.GSC CI.ISA LB.BMN LB.TPH NC.AFD NC.BBGB NC.KCPB NC.MDPB NC.PMPB NN.BEK NN.CMK6 NN.COLR NN.DSP NN.EMB NN.GWY NN.KVN NN.LCH NN.MPK NN.MZPB NN.OMMB NN.PIO NN.PLTX NN.PNT NN.PRN NN.Q09A NN.REDF NN.S11A NN.VCN NN.WLDB NN.WTNK NN.YER SN.HEL TA.R11A US.ELK US.TPNV Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 2.16e+24 dyne-cm Mw = 5.49 Z = 13 km Plane Strike Dip Rake NP1 210 75 -20 NP2 305 71 -164 Principal Axes: Axis Value Plunge Azimuth T 2.16e+24 3 258 N 0.00e+00 65 355 P -2.16e+24 25 167 Moment Tensor: (dyne-cm) Component Value Mxx -1.61e+24 Mxy 8.21e+23 Mxz 7.76e+23 Myy 1.98e+24 Myz -2.92e+23 Mzz -3.70e+23 -------------- ---------------------# ---------------------####### --------------------########## ---------------------############# ##########----------################ ###############-----################## ###################-#################### ##################----################## ##################--------################ #################-----------############## ################--------------############ ############-----------------########## T ###########-------------------######## ###########---------------------###### ###########-----------------------#### #########-------------------------## ########-------------------------- #####------------ ---------- ####------------ P --------- #------------ ------ -------------- Global CMT Convention Moment Tensor: R T P -3.70e+23 7.76e+23 2.92e+23 7.76e+23 -1.61e+24 -8.21e+23 2.92e+23 -8.21e+23 1.98e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20161228082212/index.html	Body-wave Moment Tensor (Mwb) Moment 2.545e+17 N-m Magnitude 5.5 Mwb Depth 12.0 km Percent DC 90 % Half Duration – Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 210 81 3 NP2 120 87 171 Principal Axes Axis Value Plunge Azimuth T 2.608e+17 N-m 9 75 N -0.130e+17 N-m 80 280 P -2.478e+17 N-m 4 165	December 28, 2016, CALIFORNIA-NEVADA BORDER REGION, MW=5.6 Goran Ekstrom CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C201612280822A DATA: II IU CU G IC MN LD GE DK L.P.BODY WAVES: 55S, 72C, T= 40 MANTLE WAVES: 16S, 16C, T=125 SURFACE WAVES: 139S, 267C, T= 50 TIMESTAMP: Q-20161228110948 CENTROID LOCATION: ORIGIN TIME: 08:22:14.9 0.2 LAT:38.41N 0.01;LON:118.96W 0.01 DEP: 22.2 0.8;TRIANG HDUR: 1.5 MOMENT TENSOR: SCALE 10**24 D-CM RR=-1.440 0.087; TT=-1.970 0.062 PP= 3.410 0.074; RT= 0.278 0.122 RP= 0.869 0.111; TP=-0.731 0.049 PRINCIPAL AXES: 1.(T) VAL= 3.642;PLG= 9;AZM=263 2.(N) -1.363; 60; 9 3.(P) -2.279; 28; 168 BEST DBLE.COUPLE:M0= 2.96*10**24 NP1: STRIKE=309;DIP=63;SLIP=-166 NP2: STRIKE=213;DIP=77;SLIP= -27 ----------- ------------------# ------------------##### #####-------------######### ############-----############ ################-############## ###############---############# ###############-------########### ###########---------########## T ##########------------######## #########--------------####### ##########----------------##### #########------------------#### #######--------------------## ######-------- ---------# ###--------- P -------- #--------- ------ -----------

Magnitudes

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 M_L by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for M_L is adjusted to remove a linear distance trend in residuals to give a regionally defined M_L. The defined M_L 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.

ML Magnitude

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.

Context

Waveform Inversion using wvfgrd96

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.

Location of broadband stations used for waveform inversion

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 0.02 n 3 
lp c 0.05 n 3 

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0    35    85    -5   5.16 0.3959
WVFGRD96    2.0    35    80   -10   5.26 0.4977
WVFGRD96    3.0   215    85   -10   5.29 0.5336
WVFGRD96    4.0   210    80   -30   5.35 0.5644
WVFGRD96    5.0   210    75   -30   5.38 0.5955
WVFGRD96    6.0   210    75   -25   5.39 0.6232
WVFGRD96    7.0   210    75   -25   5.41 0.6472
WVFGRD96    8.0   210    75   -30   5.45 0.6732
WVFGRD96    9.0   210    75   -25   5.45 0.6879
WVFGRD96   10.0   210    75   -25   5.47 0.6988
WVFGRD96   11.0   210    75   -25   5.48 0.7052
WVFGRD96   12.0   210    75   -20   5.48 0.7081
WVFGRD96   13.0   210    75   -20   5.49 0.7094
WVFGRD96   14.0   215    80   -20   5.49 0.7081
WVFGRD96   15.0   215    80   -20   5.50 0.7053
WVFGRD96   16.0   215    80   -20   5.51 0.7008
WVFGRD96   17.0   215    80   -20   5.51 0.6946
WVFGRD96   18.0   215    80   -15   5.52 0.6881
WVFGRD96   19.0   215    80   -15   5.53 0.6808
WVFGRD96   20.0   215    80   -15   5.53 0.6727
WVFGRD96   21.0   215    80   -15   5.54 0.6637
WVFGRD96   22.0   215    80   -15   5.54 0.6541
WVFGRD96   23.0   215    80   -15   5.55 0.6440
WVFGRD96   24.0   215    80   -15   5.55 0.6335
WVFGRD96   25.0   215    75   -15   5.56 0.6229
WVFGRD96   26.0   215    75   -15   5.57 0.6125
WVFGRD96   27.0   215    75   -10   5.57 0.6024
WVFGRD96   28.0   215    75   -10   5.58 0.5922
WVFGRD96   29.0   215    75   -10   5.58 0.5819

The best solution is

WVFGRD96   13.0   210    75   -20   5.49 0.7094

The mechanism corresponding to the best fit is

Figure 1. Waveform inversion focal mechanism

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

Figure 2. Depth sensitivity for waveform mechanism

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 0.02 n 3 
lp c 0.05 n 3 

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.

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:

• The origin time and epicentral distance are incorrect
• The velocity model used for the inversion is incorrect
• The velocity model used to define the P-arrival time is not the same as the velocity model used for the waveform inversion (assuming that the initial trace alignment is based on the P arrival time)

 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.

Velocity Model

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