Location

2008/02/21 23:57:52 41.053 -114.923 10.0 4.6 Nevada

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for

Focal Mechanism

 SLU Moment Tensor Solution
 2008/02/21 23:57:52 41.053 -114.923 10.0 4.6 Nevada
 
 Best Fitting Double Couple
    Mo = 1.04e+23 dyne-cm
    Mw = 4.61 
    Z  = 9 km
     Plane   Strike  Dip  Rake
      NP1       19    68   -118
      NP2      255    35   -40
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   1.04e+23     19     130
     N   0.00e+00     26      31
     P  -1.04e+23     57     251



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     3.56e+22
       Mxy    -5.50e+22
       Mxz    -5.17e+21
       Myy     2.69e+22
       Myz     6.86e+22
       Mzz    -6.25e+22
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ##################----              
              ######################------           
             ################----###-------          
           ##########---------------####-----        
          ########------------------#######---       
         ######---------------------##########-      
        #####----------------------############-     
        ####-----------------------#############     
       ####------------------------##############    
       ###------------------------###############    
       ##---------   -------------###############    
       #---------- P ------------################    
        ----------   -----------################     
        -----------------------#################     
         ---------------------##########   ####      
          -------------------########### T ###       
           -----------------############   ##        
             --------------################          
              -----------#################           
                 -------###############              
                     ##############                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -6.25e+22  -5.17e+21  -6.86e+22 
 -5.17e+21   3.56e+22   5.50e+22 
 -6.86e+22   5.50e+22   2.69e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080221235752/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 = 255
      DIP = 35
     RAKE = -40
       MW = 4.61
       HS = 9

The waveform inversion is preferred. The surface-wave solution is consistent.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 SLU Moment Tensor Solution
 2008/02/21 23:57:52 41.053 -114.923 10.0 4.6 Nevada
 
 Best Fitting Double Couple
    Mo = 1.04e+23 dyne-cm
    Mw = 4.61 
    Z  = 9 km
     Plane   Strike  Dip  Rake
      NP1       19    68   -118
      NP2      255    35   -40
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   1.04e+23     19     130
     N   0.00e+00     26      31
     P  -1.04e+23     57     251



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     3.56e+22
       Mxy    -5.50e+22
       Mxz    -5.17e+21
       Myy     2.69e+22
       Myz     6.86e+22
       Mzz    -6.25e+22
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ##################----              
              ######################------           
             ################----###-------          
           ##########---------------####-----        
          ########------------------#######---       
         ######---------------------##########-      
        #####----------------------############-     
        ####-----------------------#############     
       ####------------------------##############    
       ###------------------------###############    
       ##---------   -------------###############    
       #---------- P ------------################    
        ----------   -----------################     
        -----------------------#################     
         ---------------------##########   ####      
          -------------------########### T ###       
           -----------------############   ##        
             --------------################          
              -----------#################           
                 -------###############              
                     ##############                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -6.25e+22  -5.17e+21  -6.86e+22 
 -5.17e+21   3.56e+22   5.50e+22 
 -6.86e+22   5.50e+22   2.69e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080221235752/index.html
	

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 0.02 n 3
lp c 0.06 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   270    70   -15   4.25 0.3827
WVFGRD96    1.0    95    90     0   4.25 0.3904
WVFGRD96    2.0    90    75   -20   4.36 0.4446
WVFGRD96    3.0   265    45   -20   4.46 0.4670
WVFGRD96    4.0   265    35   -20   4.52 0.5287
WVFGRD96    5.0   265    35   -20   4.53 0.5785
WVFGRD96    6.0   260    35   -30   4.54 0.6116
WVFGRD96    7.0   260    40   -35   4.54 0.6306
WVFGRD96    8.0   255    35   -40   4.61 0.6517
WVFGRD96    9.0   255    35   -40   4.61 0.6550
WVFGRD96   10.0   260    40   -35   4.60 0.6491
WVFGRD96   11.0   260    40   -30   4.59 0.6358
WVFGRD96   12.0   265    45   -25   4.59 0.6223
WVFGRD96   13.0   270    50   -10   4.58 0.6077
WVFGRD96   14.0   270    50   -10   4.59 0.5932
WVFGRD96   15.0   270    50   -10   4.59 0.5767
WVFGRD96   16.0   275    55     5   4.60 0.5612
WVFGRD96   17.0   275    55     5   4.60 0.5457
WVFGRD96   18.0   275    55     5   4.60 0.5293
WVFGRD96   19.0   275    55     5   4.60 0.5125
WVFGRD96   20.0   275    55     5   4.61 0.4957
WVFGRD96   21.0   275    55     5   4.61 0.4790
WVFGRD96   22.0   275    55     5   4.62 0.4626
WVFGRD96   23.0   275    55     5   4.62 0.4466
WVFGRD96   24.0   275    55     5   4.62 0.4311
WVFGRD96   25.0   275    55     5   4.62 0.4161
WVFGRD96   26.0   275    55     5   4.63 0.4016
WVFGRD96   27.0   275    60    10   4.64 0.3881
WVFGRD96   28.0   275    60    10   4.64 0.3751
WVFGRD96   29.0   275    60    10   4.64 0.3626

The best solution is

WVFGRD96    9.0   255    35   -40   4.61 0.6550

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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was

hp c 0.02 n 3
lp c 0.06 n 3
Figure 3. Waveform comparison for depth of 8 km
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.

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=      15.00
  DIP=      74.99
 RAKE=    -125.00
  
             OR
  
  STK=     264.71
  DIP=      37.70
 RAKE=     -25.05
 
 
DEPTH = 7.0 km
 
Mw = 4.62
Best Fit 0.9154 - 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(deg)    Dist(km)   First motion
ELK       218   43 -12345
M13A       62   72 -12345
N11A      249   73 -12345
O11A      211  120 -12345
O13A      142  130 -12345
L13A       35  141 -12345
M14A       69  141 -12345
N14A       98  148 -12345
BGU        95  160 -12345
L10A      312  172 -12345
K12A        1  176 -12345
L14A       52  178 -12345
K13A       21  190 -12345
HVU        65  197 -12345
DUG       117  202 -12345
N15A       94  203 -12345
SPU        81  209 -12345
M15A       77  212 -12345
O15A      112  224 -12345
Q12A      178  224 -12345
P14A      135  226 -12345
L15A       63  237 -12345
NOQ       100  240 -12345
J12A      357  244 -12345
Q13A      161  245 -12345
K10A      321  251 -12345
L09A      296  253 -12345
Q11A      195  253 -12345
J13A       13  268 -12345
K15A       47  269 -12345
NLU       116  270 -12345
N08A      265  272 -12345
J11A      344  273 -12345
J14A       24  278 -12345
M16A       83  278 -12345
Q10A      208  278 -12345
P15A      125  279 -12345
HLID        8  282 -12345
O08A      254  286 -12345
M08A      280  293 -12345
N16A       92  294 -12345
TCU        87  295 -12345
K09A      309  296 -12345
MPU       111  302 -12345
J10A      331  304 -12345
R12A      175  304 -12345
L08A      295  312 -12345
Q09A      219  313 -12345
Q15A      136  315 -12345
P16A      119  320 -12345
I13A       12  325 -12345
I11A      345  329 -12345
R10A      202  329 -12345
J15A       37  332 -12345
I14A       20  342 -12345
N07B      266  342 -12345
N17A       91  344 -12345
WVOR      298  345 -12345
J09A      318  346 -12345
R14A      151  347 -12345
M07A      277  358 -12345
M17A       81  360 -12345
O17A      104  367 -12345
J16A       47  368 -12345
AHID       58  370 -12345
TMU       120  372 -12345
S10A      203  376 -12345
P07A      245  377 -12345
K17A       59  382 -12345
S12A      179  382 -12345
I15A       31  384 -12345
H12A        1  388 -12345
R15A      143  389 -12345
RRI2       48  392 -12345
S13A      166  396 -12345
S14A      157  396 -12345
P17A      115  397 -12345
I09A      325  399 -12345
Q16A      125  399 -12345
K07A      298  402 -12345
R08A      223  406 -12345
CCUT      160  411 -12345
N06A      267  415 -12345
DCID1      46  418 -12345
S09A      209  419 -12345
REDW       51  423 -12345
O18A      100  425 -12345
TPAW       49  425 -12345
O06A      258  427 -12345
P18A      110  428 -12345
J17A       52  432 -12345
SRU       118  433 -12345
SRU       118  433 -12345
S15A      149  435 -12345
SNOW       51  436 -12345
I08A      318  437 -12345
H15A       24  438 -12345
K18A       65  442 -12345
G12A      356  454 -12345
IMW        45  455 -12345
LOHW       50  455 -12345
T13A      169  456 -12345
BMO       336  465 -12345
T14A      160  471 -12345
L19A       74  478 -12345
BEK       256  479 -12345
R06C      236  479 -12345
G14A       14  480 -12345
O19A       98  497 -12345
MLAC      223  508 -12345
I18A       53  513 -12345
U12A      176  514 -12345
U11A      185  516 -12345
R18A      123  523 -12345
F13A        5  528 -12345
TIN       214  528 -12345
P19A      105  529 -12345
FUR       199  536 -12345
U14A      163  536 -12345
T16A      146  540 -12345
H07A      318  546 -12345
F15A       19  567 -12345
R19A      120  574 -12345
K20A       70  575 -12345
O20A       98  575 -12345
CMB       236  577 -12345
F10A      342  577 -12345
CWC       209  581 -12345
V11A      185  581 -12345
V13A      172  583 -12345
V12A      179  591 -12345
MPM       203  598 -12345
E14A       10  607 -12345
Q20A      110  612 -12345
S19A      125  619 -12345
V15A      157  629 -12345
L21A       78  638 -12345
W12A      180  638 -12345
F17A       31  640 -12345
R20A      117  645 -12345
WDC       268  645 -12345
RCT       217  647 -12345
GSC       195  659 -12345
E09A      338  660 -12345
E16A       22  662 -12345
W13A      172  667 -12345
W14A      165  668 -12345
ISA       209  674 -12345
Q21A      109  674 -12345
D14A        9  679 -12345
VES       213  683 -12345
E17A       27  684 -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

Sta Az(deg)    Dist(km)   
O11A	  212	  120
O13A	  142	  130
L13A	   35	  141
M14A	   69	  141
N14A	   98	  148
BGU	   95	  160
L10A	  312	  172
K12A	    0	  176
L14A	   52	  178
K13A	   21	  190
HVU	   65	  197
DUG	  117	  202
N15A	   94	  203
SPU	   81	  209
M15A	   77	  212
O15A	  112	  224
Q12A	  178	  224
P14A	  135	  226
L15A	   63	  237
NOQ	  100	  240
J12A	  357	  244
Q13A	  161	  245
K10A	  320	  251
L09A	  296	  253
Q11A	  194	  253
J13A	   13	  268
K15A	   47	  269
CTU	   98	  270
NLU	  116	  270
N08A	  265	  272
J11A	  344	  273
J14A	   24	  278
M16A	   83	  278
Q10A	  208	  278
P15A	  125	  279
HLID	    8	  282
O08A	  254	  286
M08A	  280	  293
N16A	   92	  294
K09A	  309	  296
MPU	  111	  302
J10A	  331	  304
R12A	  175	  304
P08A	  242	  308
L08A	  295	  312
Q09A	  219	  313
Q15A	  136	  315
P16A	  119	  320
I13A	   12	  325
I11A	  345	  329
R10A	  202	  329
J15A	   37	  332
I14A	   20	  342
N07B	  266	  342
N17A	   91	  344
WVOR	  298	  345
J09A	  318	  346
R14A	  151	  347
K08A	  303	  350
M07A	  277	  358
M17A	   81	  360
O17A	  104	  367
J16A	   47	  368
AHID	   58	  370
I10A	  336	  371
TMU	  120	  372
S10A	  203	  376
P07A	  245	  377
K17A	   59	  382
S12A	  179	  382
I15A	   31	  384
S11A	  191	  385
H12A	    1	  388
R15A	  143	  389
RRI2	   48	  392
H13A	    8	  394
S13A	  166	  396
S14A	  157	  396
P17A	  115	  397
I09A	  325	  399
Q16A	  125	  399
K07A	  298	  402
Q07A	  236	  406
R08A	  223	  406
CCUT	  160	  411
H11A	  348	  415
N06A	  267	  415
DCID1	   46	  418
S09A	  209	  419
H10A	  340	  420
REDW	   51	  423
T11A	  184	  424
O18A	  100	  425
TPAW	   49	  425
R16A	  135	  426
O06A	  258	  427
P18A	  110	  428
J17A	   52	  432
SRU	  118	  433
S15A	  149	  435
SNOW	   51	  436
I08A	  318	  437
H15A	   24	  438
K18A	   65	  442
G12A	  356	  454
IMW	   45	  455
LOHW	   50	  455
WCN	  246	  455
MOOW	   48	  456
T13A	  169	  456
H09A	  332	  460
Q18A	  116	  462
R17A	  128	  465
J18A	   58	  471
T14A	  160	  471
L19A	   74	  478
BEK	  256	  479
I17A	   47	  479
R06C	  236	  479
G14A	   14	  480
T12A	  178	  481
M19A	   82	  486
J06A	  301	  496
O19A	   98	  497
G15A	   23	  498
GRA	  206	  498
T15A	  153	  499
G10A	  340	  504
H16A	   35	  504
I07A	  313	  505
MLAC	  223	  508
I18A	   53	  513
U12A	  176	  514
DLMT	   21	  515
U11A	  185	  516
S17A	  136	  520
U13A	  170	  522
F12A	  357	  523
R18A	  123	  523
G09A	  335	  524
F13A	    5	  528
TIN	  214	  528
G16A	   28	  529
K05A	  292	  529
P19A	  105	  529
U10A	  194	  529
FUR	  199	  536
Q19A	  114	  536
U14A	  163	  536
I06A	  308	  540
T16A	  146	  540
K19A	   67	  541
F14A	   13	  543
F11A	  350	  546
L20A	   77	  559
N20A	   90	  561
S18A	  130	  565
M20A	   83	  566
F15A	   20	  567
G08A	  326	  574
R19A	  120	  574
K20A	   70	  575
O20A	   98	  575
BOZ	   26	  576
CMB	  236	  577
F10A	  342	  577
CWC	  209	  581
V11A	  184	  581
P20A	  105	  582
G17A	   34	  583
V13A	  172	  583
SHO	  192	  584
F16A	   26	  589
V12A	  179	  591
E11A	  350	  598
MPM	  203	  598
E13A	    5	  602
H06A	  315	  602
G07A	  322	  606
E14A	   10	  607
SLA	  200	  609
Q20A	  110	  612
T18A	  133	  616
U17A	  142	  617
S19A	  124	  619
V14A	  165	  622
E15A	   16	  624
N21A	   91	  624
E10A	  344	  629
V15A	  157	  629
M21A	   82	  636
O21A	   96	  637
U16A	  148	  637
L21A	   78	  638
W12A	  180	  638
F17A	   31	  640
G18A	   41	  643
R20A	  117	  645
RLMT	   44	  645
WDC	  268	  645
MSO	    7	  647
RCT	  217	  647
RWWY	   81	  649
G06A	  317	  657
LDF	  182	  658
GSC	  195	  659
E09A	  338	  660
E16A	   22	  662
LRL	  202	  664
W13A	  172	  667
W14A	  166	  668
D13A	    3	  672
F07A	  325	  673
ISA	  208	  674
Q21A	  109	  674
D11A	  351	  676
U18A	  138	  676
D14A	    9	  679
VES	  213	  683
E17A	   27	  684
F18A	   36	  684
WUAZ	  152	  688
HUMO	  287	  689
E08A	  332	  690
W15A	  160	  692
D10A	  345	  693
D15A	   15	  693
T19A	  131	  693
G05A	  314	  698
NEE2	  178	  698
GMR	  186	  699
M22A	   84	  699
HAWA	  330	  700
MVCO	  126	  700
HEC	  191	  702
RRX	  196	  709
DAN	  183	  713
N22A	   90	  714
D16A	   21	  717
D09A	  339	  720
X13A	  172	  723
W16A	  155	  725
Q22A	  107	  726
E07A	  329	  729
E18A	   32	  733
EDW2	  202	  736
V18A	  142	  736
C13A	    2	  737
SAO	  232	  739
D08A	  336	  740
C12B	  357	  741
ARV	  209	  742
PDM	  174	  752
X14A	  166	  752
ADO	  198	  755
MCCM	  247	  755
D17A	   25	  758
W17A	  150	  759
IRM	  182	  766
X15A	  161	  766
G04A	  309	  768
R22A	  112	  768
C15A	   13	  769
BBR	  194	  774
C10A	  347	  775
SMM	  216	  776
E06A	  323	  780
VCS	  202	  781
BEL	  187	  788
COR	  303	  789
OSI	  206	  789
C16A	   18	  791
D07A	  331	  793
BFS	  198	  794
CHF	  201	  794
PHWY	   85	  794
SVD	  195	  794
C09A	  342	  796
D18A	   29	  796
PHL	  220	  796
X16A	  156	  798
W18A	  144	  800
ISCO	   97	  802
C17A	   23	  803
MWC	  201	  807
Y14A	  167	  808
Y13A	  173	  809
Y12C	  177	  811
DEC	  203	  812
F04A	  314	  813
B13A	    2	  814
PASC	  202	  816
C08A	  338	  817
W19A	  142	  819
NEW	  348	  820
Y15A	  163	  820
BC3	  183	  822
B10A	  348	  826
B12A	  357	  826
T22A	  120	  826
B11A	  353	  828
B15A	   12	  828
X17A	  153	  829
D06A	  327	  830
DJJ	  203	  832
USC	  202	  835
DGR	  193	  842
C07A	  333	  843
X18A	  147	  846
MUR	  194	  851
Y16A	  158	  852
B16A	   16	  856
B09A	  344	  858
W20A	  137	  866
FMP	  201	  867
SDD	  197	  867
B17A	   21	  868
RPV	  202	  868
Z14A	  168	  871
PLM	  192	  872
EGMT	   26	  876
A13A	    2	  877
A12A	  356	  878
B08A	  338	  883
D05A	  323	  885
A11A	  353	  886
A14A	    7	  888
GLA	  179	  888
SDCO	  111	  890
Y17A	  155	  893
Z15A	  163	  896
A15A	   10	  897
C06A	  330	  898
SWS	  185	  904
A10A	  348	  905
Z16A	  159	  910
B18A	   25	  911
A16A	   16	  916
W21A	  134	  917
B07A	  335	  920
D04A	  320	  922
E03A	  314	  924
113A	  173	  925
A09A	  343	  926
109C	  193	  927
Y19A	  146	  933
DVT	  187	  937
A17A	   19	  938
LAO	   45	  938
114A	  168	  939
A08A	  340	  942
BAR	  190	  942
112A	  178	  946
Z17A	  154	  947
RSSD	   66	  955
115A	  165	  957
SNCC	  207	  957
A18A	   23	  961
W22A	  131	  969
B06A	  330	  978
116A	  162	  985
Z18A	  152	  985
A07A	  336	  987
Z19A	  148	  997
NLWA	  318	 1002
ANMO	  130	 1005
X22A	  134	 1006
117A	  157	 1012
214A	  169	 1027
118A	  153	 1032
A06A	  332	 1032
TUC	  158	 1038
119A	  150	 1047
A05A	  330	 1047
Y22D	  135	 1047
216A	  162	 1051
OGNE	   86	 1084
217A	  159	 1093
120A	  147	 1098
218A	  155	 1098
219A	  152	 1125
318A	  156	 1155
122A	  140	 1164
DGMT	   42	 1181
319A	  153	 1187
CBKS	   96	 1320
AMTX	  116	 1348
ECSD	   73	 1533
KSU1	   92	 1574
WMOK	  111	 1580
AGMN	   56	 1706
JCT	  126	 1797
CIA	  201	 1811
SCIA	   80	 1811
MIAR	  104	 2007
JFWS	   76	 2048
CCM	  247	 2056
NATX	  113	 2082
UALR	  102	 2097
HKT	  120	 2116
SLM	   89	 2123
FVM	   91	 2127
COWI	   66	 2146
HDIL	   83	 2156
BMO	  336	 2169
PBMO	   95	 2169
SIUC	   91	 2237
PVMO	   95	 2244
MPH	   99	 2280
OLIL	   88	 2299
OXF	  100	 2352
USIN	   89	 2359
VBMS	  106	 2382
WVT	   94	 2412
BLO	   86	 2420
PLAL	   97	 2441
GLMI	   70	 2494
AAM	   76	 2592
ACSO	   81	 2688
BRAL	  105	 2723
TZTN	   90	 2756
ALLY	   77	 2891
ERPA	   76	 2895
GOGA	   97	 2899
MCWV	   81	 2964
BLA	   87	 2994
SSPA	   78	 3099
NHSC	   95	 3189
CBN	   83	 3214
BINY	   75	 3219
SDMD	   81	 3220
MVL	   79	 3244
DWPF	  105	 3364
ACCN	   72	 3381
PAL	   76	 3417
CPNY	   77	 3418
LBNH	   70	 3503

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 0.02 n 3
lp c 0.06 n 3

Discussion

The Future

Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.

Acknowledgements

Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.

Appendix A


Spectra fit plots to each station

Velocity Model

The WUS 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:

DATE=Sun Feb 24 17:56:41 CST 2008

Last Changed 2008/02/21