Location

2008/02/21 14:16:05 41.076 -114.771 10.0 6.3 Nevada

Arrival Times (from USGS)

Felt Map

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2008/02/21 14:16:05:0 41.08 -114.77 10.0 6.3 Nevada Stations used: IW.DCID1 IW.IMW IW.LOHW IW.MOOW IW.REDW IW.RRI2 IW.SNOW IW.TPAW NN.BEK NN.WCN TA.G13A TA.G14A TA.G15A TA.H08A TA.H09A TA.H10A TA.H11A TA.H12A TA.H13A TA.H15A TA.H16A TA.I08A TA.I09A TA.I11A TA.I12A TA.I13A TA.I14A TA.I15A TA.I16A TA.I17A TA.J07A TA.J08A TA.J10A TA.J11A TA.J12A TA.J13A TA.J14A TA.J15A TA.J16A TA.J17A TA.J18A TA.K07A TA.K08A TA.K09A TA.K10A TA.K12A TA.K13A TA.K14A TA.K15A TA.K16A TA.K17A TA.K18A TA.L07A TA.L08A TA.L09A TA.L10A TA.L11A TA.L12A TA.L13A TA.L14A TA.L15A TA.L16A TA.L17A TA.L18A TA.L19A TA.M07A TA.M09A TA.M10A TA.M11A TA.M13A TA.M14A TA.M15A TA.M16A TA.M17A TA.M18A TA.M19A TA.N06A TA.N07B TA.N08A TA.N09A TA.N10A TA.N11A TA.N13A TA.N14A TA.N15A TA.N16A TA.N17A TA.O06A TA.O07A TA.O08A TA.O09A TA.O10A TA.O11A TA.O12A TA.O13A TA.O15A TA.O17A TA.O18A TA.O19A TA.P06A TA.P07A TA.P08A TA.P09A TA.P10A TA.P11A TA.P12A TA.P14A TA.P15A TA.P16A TA.P17A TA.P18A TA.Q07A TA.Q08A TA.Q09A TA.Q10A TA.Q11A TA.Q12A TA.Q13A TA.Q14A TA.Q15A TA.Q16A TA.R06C TA.R08A TA.R09A TA.R10A TA.R11A TA.R12A TA.R13A TA.R14A TA.R15A TA.R16A TA.R17A TA.S09A TA.S10A TA.S11A TA.S12A TA.S13A TA.S14A TA.S15A TA.T11A TA.T12A TA.T13A TA.T14A TA.T15A US.AHID US.BMO US.BW06 US.DUG US.ELK US.HLID US.WVOR UU.SRU Filtering commands used: hp c 0.01 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 8.91e+24 dyne-cm Mw = 5.90 Z = 11 km Plane Strike Dip Rake NP1 205 50 -95 NP2 33 40 -84 Principal Axes: Axis Value Plunge Azimuth T 8.91e+24 5 299 N 0.00e+00 4 208 P -8.91e+24 84 80 Moment Tensor: (dyne-cm) Component Value Mxx 2.02e+24 Mxy -3.73e+24 Mxz 1.99e+23 Myy 6.73e+24 Myz -1.61e+24 Mzz -8.74e+24 ############## ###############------- ##############------------## #############---------------## ############------------------### T ###########-------------------#### #########---------------------##### ############----------------------###### ###########-----------------------###### ###########------------ ---------####### ###########------------ P ---------####### ##########------------- --------######## ##########-----------------------######### ########------------------------######## ########-----------------------######### #######---------------------########## ######--------------------########## #####------------------########### ####--------------############ ####----------############## #----################# ############## Global CMT Convention Moment Tensor: R T P -8.74e+24 1.99e+23 1.61e+24 1.99e+23 2.02e+24 3.73e+24 1.61e+24 3.73e+24 6.73e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080221141605/index.html

Preferred Solution

The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is

      STK = 205
      DIP = 50
     RAKE = -95
       MW = 5.90
       HS = 11.0

The NDK file is 20080221141605.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU USGSMT CMT GCMT UCB USGSCMT SLUFM

USGS/SLU Moment Tensor Solution ENS 2008/02/21 14:16:05:0 41.08 -114.77 10.0 6.3 Nevada Stations used: IW.DCID1 IW.IMW IW.LOHW IW.MOOW IW.REDW IW.RRI2 IW.SNOW IW.TPAW NN.BEK NN.WCN TA.G13A TA.G14A TA.G15A TA.H08A TA.H09A TA.H10A TA.H11A TA.H12A TA.H13A TA.H15A TA.H16A TA.I08A TA.I09A TA.I11A TA.I12A TA.I13A TA.I14A TA.I15A TA.I16A TA.I17A TA.J07A TA.J08A TA.J10A TA.J11A TA.J12A TA.J13A TA.J14A TA.J15A TA.J16A TA.J17A TA.J18A TA.K07A TA.K08A TA.K09A TA.K10A TA.K12A TA.K13A TA.K14A TA.K15A TA.K16A TA.K17A TA.K18A TA.L07A TA.L08A TA.L09A TA.L10A TA.L11A TA.L12A TA.L13A TA.L14A TA.L15A TA.L16A TA.L17A TA.L18A TA.L19A TA.M07A TA.M09A TA.M10A TA.M11A TA.M13A TA.M14A TA.M15A TA.M16A TA.M17A TA.M18A TA.M19A TA.N06A TA.N07B TA.N08A TA.N09A TA.N10A TA.N11A TA.N13A TA.N14A TA.N15A TA.N16A TA.N17A TA.O06A TA.O07A TA.O08A TA.O09A TA.O10A TA.O11A TA.O12A TA.O13A TA.O15A TA.O17A TA.O18A TA.O19A TA.P06A TA.P07A TA.P08A TA.P09A TA.P10A TA.P11A TA.P12A TA.P14A TA.P15A TA.P16A TA.P17A TA.P18A TA.Q07A TA.Q08A TA.Q09A TA.Q10A TA.Q11A TA.Q12A TA.Q13A TA.Q14A TA.Q15A TA.Q16A TA.R06C TA.R08A TA.R09A TA.R10A TA.R11A TA.R12A TA.R13A TA.R14A TA.R15A TA.R16A TA.R17A TA.S09A TA.S10A TA.S11A TA.S12A TA.S13A TA.S14A TA.S15A TA.T11A TA.T12A TA.T13A TA.T14A TA.T15A US.AHID US.BMO US.BW06 US.DUG US.ELK US.HLID US.WVOR UU.SRU Filtering commands used: hp c 0.01 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 8.91e+24 dyne-cm Mw = 5.90 Z = 11 km Plane Strike Dip Rake NP1 205 50 -95 NP2 33 40 -84 Principal Axes: Axis Value Plunge Azimuth T 8.91e+24 5 299 N 0.00e+00 4 208 P -8.91e+24 84 80 Moment Tensor: (dyne-cm) Component Value Mxx 2.02e+24 Mxy -3.73e+24 Mxz 1.99e+23 Myy 6.73e+24 Myz -1.61e+24 Mzz -8.74e+24 ############## ###############------- ##############------------## #############---------------## ############------------------### T ###########-------------------#### #########---------------------##### ############----------------------###### ###########-----------------------###### ###########------------ ---------####### ###########------------ P ---------####### ##########------------- --------######## ##########-----------------------######### ########------------------------######## ########-----------------------######### #######---------------------########## ######--------------------########## #####------------------########### ####--------------############ ####----------############## #----################# ############## Global CMT Convention Moment Tensor: R T P -8.74e+24 1.99e+23 1.61e+24 1.99e+23 2.02e+24 3.73e+24 1.61e+24 3.73e+24 6.73e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080221141605/index.html USGS/SLU Moment Tensor Solution ENS 2008/21/14 16:05:00:0 0.08 -114.77 10.0 6.3 Nevada Stations used: IW.DCID1 IW.IMW IW.LOHW IW.MOOW IW.REDW IW.RRI2 IW.SNOW IW.TPAW NN.BEK NN.WCN TA.G13A TA.G14A TA.G15A TA.H08A TA.H09A TA.H10A TA.H11A TA.H12A TA.H13A TA.H15A TA.H16A TA.I08A TA.I09A TA.I11A TA.I12A TA.I13A TA.I14A TA.I15A TA.I16A TA.I17A TA.J07A TA.J08A TA.J10A TA.J11A TA.J12A TA.J13A TA.J14A TA.J15A TA.J16A TA.J17A TA.J18A TA.K07A TA.K08A TA.K09A TA.K10A TA.K12A TA.K13A TA.K14A TA.K15A TA.K16A TA.K17A TA.K18A TA.L07A TA.L08A TA.L09A TA.L10A TA.L11A TA.L12A TA.L13A TA.L14A TA.L15A TA.L16A TA.L17A TA.L18A TA.L19A TA.M07A TA.M09A TA.M10A TA.M11A TA.M13A TA.M14A TA.M15A TA.M16A TA.M17A TA.M18A TA.M19A TA.N06A TA.N07B TA.N08A TA.N09A TA.N10A TA.N11A TA.N13A TA.N14A TA.N15A TA.N16A TA.N17A TA.O06A TA.O07A TA.O08A TA.O09A TA.O10A TA.O11A TA.O12A TA.O13A TA.O15A TA.O17A TA.O18A TA.O19A TA.P06A TA.P07A TA.P08A TA.P09A TA.P10A TA.P11A TA.P12A TA.P14A TA.P15A TA.P16A TA.P17A TA.P18A TA.Q07A TA.Q08A TA.Q09A TA.Q10A TA.Q11A TA.Q12A TA.Q13A TA.Q14A TA.Q15A TA.Q16A TA.R06C TA.R08A TA.R09A TA.R10A TA.R11A TA.R12A TA.R13A TA.R14A TA.R15A TA.R16A TA.R17A TA.S09A TA.S10A TA.S11A TA.S12A TA.S13A TA.S14A TA.S15A TA.T11A TA.T12A TA.T13A TA.T14A TA.T15A US.AHID US.BMO US.BW06 US.DUG US.ELK US.HLID US.WVOR UU.SRU Filtering commands used: hp c 0.01 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 8.91e+24 dyne-cm Mw = 5.90 Z = 11 km Plane Strike Dip Rake NP1 205 50 -95 NP2 33 40 -84 Principal Axes: Axis Value Plunge Azimuth T 8.91e+24 5 299 N 0.00e+00 4 208 P -8.91e+24 84 80 Moment Tensor: (dyne-cm) Component Value Mxx 2.02e+24 Mxy -3.73e+24 Mxz 1.99e+23 Myy 6.73e+24 Myz -1.61e+24 Mzz -8.74e+24 ############## ###############------- ##############------------## #############---------------## ############------------------### T ###########-------------------#### #########---------------------##### ############----------------------###### ###########-----------------------###### ###########------------ ---------####### ###########------------ P ---------####### ##########------------- --------######## ##########-----------------------######### ########------------------------######## ########-----------------------######### #######---------------------########## ######--------------------########## #####------------------########### ####--------------############ ####----------############## #----################# ############## Global CMT Convention Moment Tensor: R T P -8.74e+24 1.99e+23 1.61e+24 1.99e+23 2.02e+24 3.73e+24 1.61e+24 3.73e+24 6.73e+24

USGS Body-Wave Moment Tensor Solution 08/02/21 14:16:03.82 NEVADA Epicenter: 41.083 -114.730 MW 5.8 USGS MOMENT TENSOR SOLUTION Depth 7 No. of sta: 91 Moment Tensor; Scale 10**17 Nm Mrr=-6.82 Mtt= 2.12 Mpp= 4.70 Mrt= 1.59 Mrp= 2.38 Mtp= 1.19 Principal axes: T Val= 5.79 Plg=12 Azm=293 N 1.69 3 23 P -7.48 76 128 Best Double Couple:Mo=6.8*10**17 NP1:Strike=206 Dip=58 Slip= -86 NP2: 19 33 -96 ####### ################# ##############-----## #############---------### #############------------#### # #########-------------##### # T ########---------------#### ## #######----------------##### ###########-----------------##### ##########------- --------##### #########-------- P -------###### #########-------- -------###### #######------------------###### #######-----------------####### ######----------------####### ####--------------####### ##------------####### #-------######### #######

February 21, 2008, NEVADA, MW=6.0 Goran Ekstrom CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C200802211416A DATA: II IU CU IC G GE L.P.BODY WAVES: 92S, 209C, T= 40 MANTLE WAVES: 83S, 120C, T=125 SURFACE WAVES: 99S, 252C, T= 50 TIMESTAMP: Q-20080221151936 CENTROID LOCATION: ORIGIN TIME: 14:16:10.1 0.1 LAT:41.23N 0.01;LON:114.86W 0.01 DEP: 14.1 0.2;TRIANG HDUR: 2.5 MOMENT TENSOR: SCALE 10**25 D-CM RR=-1.230 0.010; TT= 0.245 0.008 PP= 0.990 0.009; RT=-0.078 0.018 RP= 0.125 0.018; TP= 0.628 0.007 PRINCIPAL AXES: 1.(T) VAL= 1.350;PLG= 2;AZM=300 2.(N) -0.098; 7; 209 3.(P) -1.247; 83; 43 BEST DBLE.COUPLE:M0= 1.30*10**25 NP1: STRIKE= 36;DIP=44;SLIP= -81 NP2: STRIKE=203;DIP=47;SLIP= -99 ########### ###########-------- ##########------------# #########--------------### T #######-----------------### ######------------------#### ########-------------------#### ########-------- ---------##### ########-------- P --------###### #######--------- -------####### #######-------------------####### ######-----------------######## ######----------------######### #####--------------########## ####------------########### ###--------############ --################# ###########

February 21, 2008, NEVADA, MW=6.0 Goran Ekstrom CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C200802211416A DATA: II IU CU IC G GE L.P.BODY WAVES: 92S, 209C, T= 40 MANTLE WAVES: 83S, 120C, T=125 SURFACE WAVES: 99S, 252C, T= 50 TIMESTAMP: Q-20080221151936 CENTROID LOCATION: ORIGIN TIME: 14:16:10.1 0.1 LAT:41.23N 0.01;LON:114.86W 0.01 DEP: 14.1 0.2;TRIANG HDUR: 2.5 MOMENT TENSOR: SCALE 10**25 D-CM RR=-1.230 0.010; TT= 0.245 0.008 PP= 0.990 0.009; RT=-0.078 0.018 RP= 0.125 0.018; TP= 0.628 0.007 PRINCIPAL AXES: 1.(T) VAL= 1.350;PLG= 2;AZM=300 2.(N) -0.098; 7; 209 3.(P) -1.247; 83; 43 BEST DBLE.COUPLE:M0= 1.30*10**25 NP1: STRIKE= 36;DIP=44;SLIP= -81 NP2: STRIKE=203;DIP=47;SLIP= -99 ########### ###########-------- ##########------------# #########--------------### T #######-----------------### ######------------------#### ########-------------------#### ########-------- ---------##### ########-------- P --------###### #######--------- -------####### #######-------------------####### ######-----------------######## ######----------------######### #####--------------########## ####------------########### ###--------############ --################# ###########

UCB Seismological Laboratory Inversion method: complete waveform Stations used: CMB KCC ORV Berkeley Moment Tensor Solution Best Fitting Double-Couple: Mo = 1.04E+25 Dyne-cm Mw = 5.95 Z = 11 Plane Strike Rake Dip NP1 228 -71 65 NP2 10 -124 31 Principal Axes: Axis Value Plunge Azimuth T 10.400 18 305 N 0.000 17 40 P -10.400 65 171 Event Date/Time: February 21, 2008 at 14:16:05 UTC Event ID: usus2008nsa9 Moment Tensor: Scale = 10**24 Dyne-cm Component Value Mxx 1.254 Mxy -4.116 Mxz 5.612 Myy 6.359 Myz -3.121 Mzz -7.613 ####### ################--- #####################---- ########################----- ###########################-##### ## ###################-----###### ### T ###############----------###### #### ############-------------####### #################----------------###### ################------------------####### ##############--------------------####### ############----------------------####### ###########-----------------------####### ##########---------- -----------####### #######------------ P ----------####### ######------------- ---------######## #####------------------------######## ###------------------------######## #------------------------######## ---------------------######## -----------------######## -----------######## ####### Lower Hemisphere Equiangle Projection

USGS Centroid Moment Tensor Solution 08/02/21 14:16:03.82 NEVADA Epicenter: 41.083 -114.730 MW 6.0 USGS CENTROID MOMENT TENSOR 08/02/21 14:16:41.29 Centroid: 42.125 -113.949 Depth 10 No. of sta: 60 Moment Tensor; Scale 10**18 Nm Mrr=-1.12 Mtt= 0.26 Mpp= 0.85 Mrt= 0.29 Mrp=-0.60 Mtp= 0.53 Principal axes: T Val= 1.23 Plg= 9 Azm=116 N 0.16 20 22 P -1.40 66 229 Best Double Couple:Mo=1.3*10**18 NP1:Strike= 9 Dip=58 Slip=-114 NP2: 230 40 -55 ######- ############----- ###############------ #############-----####### ###########---------######### ##########------------######### ########--------------######### #######----------------########## ######-----------------########## #####------------------########## ####-------- -------########### ####-------- P -------########### ##--------- ------######## ##------------------######## T #-----------------######### ---------------########## ------------######### --------######### -######

First motions and takeoff angles from an elocate run.

Magnitudes

ML Magnitude

(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.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

Waveform Inversion

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.

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 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 0.01 n 3
lp c 0.05 n 3

The results of this grid search from 0.5 to 19 km depth are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5    75    90    15   5.47 0.3480
WVFGRD96    1.0   255    90   -10   5.49 0.3692
WVFGRD96    2.0    75    75    -5   5.58 0.4315
WVFGRD96    3.0    70    50   -10   5.67 0.4634
WVFGRD96    4.0    70    45   -15   5.71 0.4994
WVFGRD96    5.0    70    45   -15   5.73 0.5362
WVFGRD96    6.0    65    45   -25   5.75 0.5714
WVFGRD96    7.0    50    40   -55   5.81 0.6128
WVFGRD96    8.0    45    35   -65   5.87 0.6595
WVFGRD96    9.0    40    40   -75   5.90 0.7115
WVFGRD96   10.0    35    40   -80   5.90 0.7386
WVFGRD96   11.0   205    50   -95   5.90 0.7412
WVFGRD96   12.0   205    50   -95   5.90 0.7254
WVFGRD96   13.0   200    50  -105   5.89 0.6988
WVFGRD96   14.0    50    45   -60   5.87 0.6700
WVFGRD96   15.0    65    55   -30   5.84 0.6500
WVFGRD96   16.0    70    60   -20   5.84 0.6350
WVFGRD96   17.0    70    65   -20   5.84 0.6216
WVFGRD96   18.0    70    65   -15   5.85 0.6096
WVFGRD96   19.0    70    65   -15   5.85 0.5972
WVFGRD96   20.0    75    70   -10   5.86 0.5847
WVFGRD96   21.0    75    70   -10   5.86 0.5730
WVFGRD96   22.0    75    70    -5   5.86 0.5602
WVFGRD96   23.0    75    75     5   5.87 0.5488
WVFGRD96   24.0    75    75     5   5.87 0.5372
WVFGRD96   25.0    75    75     5   5.88 0.5253
WVFGRD96   26.0    75    75     5   5.88 0.5131
WVFGRD96   27.0    75    75     5   5.89 0.5012
WVFGRD96   28.0    75    75     5   5.89 0.4894
WVFGRD96   29.0    75    80     5   5.90 0.4782

The best solution is

WVFGRD96   11.0   205    50   -95   5.90 0.7412

The mechanism correspond 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 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 0.01 n 3
lp c 0.05 n 3

Figure 3. Waveform comparison for selected depth

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:

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)

Assuming only a mislocation, the time shifts are fit to a functional form:

 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.

Surface-Wave Focal Mechanism

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

Location of broadband stations used to obtain focal mechanism from surface-wave spectral amplitudes

The surface-wave determined focal mechanism is shown here.


  NODAL PLANES 

  
  STK=     194.99
  DIP=      55.00
 RAKE=    -104.99
  
             OR
  
  STK=      40.01
  DIP=      37.70
 RAKE=     -69.72
 
 
DEPTH = 10.0 km
 
Mw = 5.97
Best Fit 0.8931 - P-T axis plot gives solutions with FIT greater than FIT90

First motion data

The P-wave first motion data for focal mechanism studies are as follow:

Sta Az    Dist   First motion
N12A      222   34 -12345
ELK       227   54 -12345
N13A      117   54 -12345
M13A       58   60 -12345
N11A      251   86 -12345
O12A      179   90 -12345
M11A      295   94 -12345
L12A      350  121 -12345
O13A      147  124 -12345
M14A       68  128 -12345
O11A      216  129 -12345
L13A       31  132 -12345
N14A      100  136 -12345
L11A      326  146 -12345
N10A      255  152 -12345
M10A      289  156 -12345
L14A       50  166 -12345
O10A      240  170 -12345
K12A      356  174 -12345
P12A      184  178 -12345
L10A      309  180 -12345
K13A       18  184 -12345
P11A      207  189 -12345
N15A       95  191 -12345
DUG       120  192 -12345
M15A       77  199 -12345
K14A       39  210 -12345
O15A      114  214 -12345
P10A      222  216 -12345
P14A      138  219 -12345
L15A       62  224 -12345
Q12A      181  226 -12345
M09A      281  228 -12345
O09A      245  228 -12345
N09A      265  233 -12345
J12A      354  243 -12345
Q13A      165  244 -12345
K10A      318  257 -12345
K15A       45  258 -12345
Q11A      197  259 -12345
J13A       11  263 -12345
L09A      294  263 -12345
P09A      231  263 -12345
M16A       83  265 -12345
Q14A      151  265 -12345
J14A       22  270 -12345
P15A      127  270 -12345
J11A      342  274 -12345
HLID        6  278 -12345
N16A       93  281 -12345
N08A      265  285 -12345
Q10A      210  286 -12345
L16A       68  297 -12345
O08A      254  299 -12345
I12A      354  303 -12345
K09A      307  304 -12345
R12A      177  305 -12345
Q15A      138  308 -12345
J10A      328  309 -12345
P16A      121  310 -12345
R11A      193  311 -12345
I13A        9  320 -12345
P08A      242  320 -12345
J15A       36  322 -12345
L08A      294  322 -12345
Q09A      220  323 -12345
K16A       52  328 -12345
R13A      168  329 -12345
I11A      343  330 -12345
N17A       91  332 -12345
I14A       18  335 -12345
R10A      203  336 -12345
R14A      153  343 -12345
L17A       69  344 -12345
M17A       81  347 -12345
N07B      266  355 -12345
O17A      105  355 -12345
WVOR      296  355 -12345
J16A       46  357 -12345
AHID       57  358 -12345
K08A      302  359 -12345
O07A      255  362 -12345
Q08A      229  365 -12345
K17A       59  370 -12345
M07A      277  370 -12345
R09A      213  372 -12345
I15A       29  375 -12345
RRI2       47  381 -12345
R15A      145  383 -12345
S10A      205  384 -12345
S12A      181  385 -12345
H12A      359  386 -12345
P17A      116  386 -12345
P07A      245  389 -12345
H13A        6  390 -12345
Q16A      127  390 -12345
S11A      193  390 -12345
S14A      159  393 -12345
L07A      287  395 -12345
M18A       83  396 -12345
S13A      168  396 -12345
J08A      311  397 -12345
I09A      324  404 -12345
L18A       75  406 -12345
DCID1      45  407 -12345
REDW       51  411 -12345
I16A       40  412 -12345
K07A      297  412 -12345
O18A      101  413 -12345
TPAW       48  414 -12345
H11A      346  416 -12345
R08A      224  416 -12345
P18A      111  417 -12345
Q07A      237  418 -12345
R16A      137  419 -12345
J17A       51  420 -12345
H10A      338  422 -12345
SRU       120  423 -12345
SNOW       50  424 -12345
N06A      267  428 -12345
S09A      210  428 -12345
T11A      185  428 -12345
K18A       65  429 -12345
H15A       23  430 -12345
S15A      150  431 -12345
O06A      258  440 -12345
I08A      317  443 -12345
IMW        44  444 -12345
LOHW       49  444 -12345
MOOW       47  445 -12345
G13A        5  448 -12345
J07A      306  453 -12345
R17A      129  456 -12345
T13A      170  456 -12345
J18A       57  459 -12345
P06A      252  462 -12345
H09A      330  463 -12345
L19A       74  465 -12345
BMO       335  468 -12345
I17A       46  468 -12345
WCN       247  468 -12345
T14A      161  469 -12345
BW06       65  471 -12345
M19A       82  473 -12345
G14A       13  475 -12345
T12A      179  483 -12345
O19A       98  485 -12345
G15A       21  491 -12345
R06C      236  491 -12345
BEK       256  492 -12345
H16A       34  495 -12345
T15A      155  496 -12345
H08A      321  498 -12345

Surface-wave analysis

Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.

Data preparation

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 Love-wave spectral amplitudes, respectively. These were input to the search program which examined all depths between 1 and 25 km and all possible mechanisms.

Best mechanism fit as a function of depth. The preferred depth is given above. Lower hemisphere projection

Pressure-tension axis trends. Since the surface-wave 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 T-axes 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 0-180 degrees are sampled.

Love-wave radiation patterns

Rayleigh-wave radiation patterns

Broadband station distribution

The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used

Waveform comparison for this mechanism

Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave 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, R-radial 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 0.01 n 3
lp c 0.05 n 3

Discussion

Acknowledgements

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.

Appendix A

Spectra fit plots to each station

Velocity Model

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
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

Quality Control

Here we tabulate the reasons for not using certain digital data sets

The following stations did not have a valid response files:

Last Changed Mon Dec 7 02:19:49 CST 2015