2008/02/28 15:10:39 41.036 -114.897 10.0 3.9 Nevada
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/02/28 15:10:39 41.036 -114.897 10.0 3.9 Nevada
Best Fitting Double Couple
Mo = 1.17e+22 dyne-cm
Mw = 3.98
Z = 10 km
Plane Strike Dip Rake
NP1 22 61 -118
NP2 250 40 -50
Principal Axes:
Axis Value Plunge Azimuth
T 1.17e+22 11 132
N 0.00e+00 24 37
P -1.17e+22 63 245
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.71e+21
Mxy -6.57e+21
Mxz 5.10e+20
Myy 4.16e+21
Myz 5.97e+21
Mzz -8.86e+21
##############
####################--
#######################-----
########################------
##############-------------##-----
##########------------------######--
########---------------------########-
#######----------------------###########
#####------------------------###########
#####-------------------------############
####-------------------------#############
###---------- -------------#############
##----------- P ------------##############
#----------- -----------##############
#------------------------###############
-----------------------###############
---------------------######### ###
-------------------########## T ##
---------------############
------------################
------################
##############
Harvard Convention
Moment Tensor:
R T F
-8.86e+21 5.10e+20 -5.97e+21
5.10e+20 4.71e+21 6.57e+21
-5.97e+21 6.57e+21 4.16e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20080228151039/index.html
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STK = 250
DIP = 40
RAKE = -50
MW = 3.98
HS = 10.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/02/28 15:10:39 41.036 -114.897 10.0 3.9 Nevada
Best Fitting Double Couple
Mo = 1.17e+22 dyne-cm
Mw = 3.98
Z = 10 km
Plane Strike Dip Rake
NP1 22 61 -118
NP2 250 40 -50
Principal Axes:
Axis Value Plunge Azimuth
T 1.17e+22 11 132
N 0.00e+00 24 37
P -1.17e+22 63 245
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.71e+21
Mxy -6.57e+21
Mxz 5.10e+20
Myy 4.16e+21
Myz 5.97e+21
Mzz -8.86e+21
##############
####################--
#######################-----
########################------
##############-------------##-----
##########------------------######--
########---------------------########-
#######----------------------###########
#####------------------------###########
#####-------------------------############
####-------------------------#############
###---------- -------------#############
##----------- P ------------##############
#----------- -----------##############
#------------------------###############
-----------------------###############
---------------------######### ###
-------------------########## T ##
---------------############
------------################
------################
##############
Harvard Convention
Moment Tensor:
R T F
-8.86e+21 5.10e+20 -5.97e+21
5.10e+20 4.71e+21 6.57e+21
-5.97e+21 6.57e+21 4.16e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20080228151039/index.html
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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.
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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 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 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 220 45 -90 3.59 0.2571
WVFGRD96 1.0 270 90 -5 3.49 0.2136
WVFGRD96 2.0 85 65 -20 3.65 0.2567
WVFGRD96 3.0 100 30 10 3.78 0.2894
WVFGRD96 4.0 270 30 -10 3.81 0.3507
WVFGRD96 5.0 260 30 -30 3.84 0.3996
WVFGRD96 6.0 260 35 -30 3.85 0.4353
WVFGRD96 7.0 255 35 -40 3.87 0.4597
WVFGRD96 8.0 250 35 -45 3.95 0.4791
WVFGRD96 9.0 250 35 -50 3.97 0.4899
WVFGRD96 10.0 250 40 -50 3.98 0.4926
WVFGRD96 11.0 250 40 -50 3.99 0.4868
WVFGRD96 12.0 255 40 -40 3.99 0.4761
WVFGRD96 13.0 260 45 -35 4.00 0.4623
WVFGRD96 14.0 260 45 -35 4.01 0.4458
WVFGRD96 15.0 260 45 -30 4.02 0.4273
WVFGRD96 16.0 260 45 -30 4.02 0.4073
WVFGRD96 17.0 265 45 -25 4.03 0.3862
WVFGRD96 18.0 265 45 -25 4.03 0.3649
WVFGRD96 19.0 265 45 -20 4.04 0.3438
WVFGRD96 20.0 265 45 -20 4.04 0.3228
WVFGRD96 21.0 265 45 -20 4.05 0.3030
WVFGRD96 22.0 265 45 -20 4.05 0.2830
WVFGRD96 23.0 265 45 -20 4.05 0.2643
WVFGRD96 24.0 265 50 -20 4.06 0.2471
WVFGRD96 25.0 265 50 -20 4.06 0.2316
WVFGRD96 26.0 190 75 50 4.06 0.2210
WVFGRD96 27.0 190 75 45 4.06 0.2153
WVFGRD96 28.0 190 75 45 4.07 0.2099
WVFGRD96 29.0 185 80 45 4.07 0.2051
The best solution is
WVFGRD96 10.0 250 40 -50 3.98 0.4926
The mechanism correspond 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 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 0.10 n 3
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| 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. |
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.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES
STK= 30.00
DIP= 59.99
RAKE= -115.00
OR
STK= 253.00
DIP= 38.29
RAKE= -53.80
DEPTH = 8.0 km
Mw = 4.07
Best Fit 0.9117 - P-T axis plot gives solutions with FIT greater than FIT90
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The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion N12A 210 24 -12345 ELK 222 43 -12345 N13A 109 62 -12345 M13A 59 71 -12345 N11A 251 75 -12345 O12A 171 86 -12345 M11A 301 87 -12345 O11A 213 119 -12345 L12A 355 124 -12345 O13A 142 127 -12345 M14A 68 140 -12345 L13A 34 141 -12345 L11A 331 145 -12345 N14A 98 145 -12345 M10A 292 148 -12345 BGU 94 158 -12345 L10A 312 175 -12345 L14A 51 177 -12345 K12A 360 178 -12345 P11A 204 180 -12345 K13A 20 191 -12345 P13A 157 191 -12345 DUG 117 200 -12345 N15A 94 201 -12345 SPU 81 208 -12345 M15A 76 211 -12345 O09A 244 217 -12345 M09A 282 218 -12345 K14A 40 220 -12345 N09A 266 222 -12345 O15A 111 222 -12345 Q12A 178 222 -12345 P14A 135 223 -12345 L15A 62 236 -12345 Q13A 162 243 -12345 P09A 230 252 -12345 Q11A 195 252 -12345 K10A 320 253 -12345 L09A 296 256 -12345 Q14A 148 266 -12345 NLU 116 268 -12345 J13A 13 269 -12345 K15A 46 269 -12345 N08A 265 274 -12345 M16A 82 276 -12345 P15A 125 276 -12345 Q10A 208 277 -12345 J14A 24 278 -12345 HLID 8 283 -12345 O08A 254 288 -12345 N16A 92 292 -12345 M08A 280 295 -12345 K09A 309 299 -12345 MPU 111 299 -12345 R12A 175 302 -12345 R11A 191 304 -12345 L16A 68 309 -12345 Q15A 136 312 -12345 Q09A 219 313 -12345 L08A 295 315 -12345 I13A 11 326 -12345 R13A 166 327 -12345 I11A 345 331 -12345 K16A 53 339 -12345 N17A 90 342 -12345 I14A 20 343 -12345 N07B 267 344 -12345 R14A 151 344 -12345 WVOR 298 348 -12345 O07A 255 351 -12345 K08A 303 352 -12345 Q08A 228 354 -12345 L17A 69 356 -12345 M17A 81 358 -12345 M07A 278 361 -12345 O17A 104 364 -12345 AHID 57 369 -12345 K17A 59 381 -12345 I15A 30 384 -12345 L07A 288 386 -12345 P17A 115 394 -12345 S13A 167 394 -12345 M18A 82 407 -12345 N06A 267 417 -12345 L18A 75 418 -12345 O18A 100 422 -12345 T11A 184 422 -12345 J17A 52 432 -12345 K18A 65 441 -12345 G13A 7 454 -12345 J18A 57 470 -12345
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.
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.
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| 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. |
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| 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. |
The distribution of broadband stations with azimuth and distance is
Sta Az(deg) Dist(km) O11A 213 119 L12A 355 124 M14A 68 140 N10A 256 140 L13A 34 141 L11A 331 144 N14A 98 145 M10A 292 148 BGU 94 158 L10A 312 175 L14A 51 177 K12A 360 178 P11A 204 180 K13A 20 191 P13A 157 191 HVU 64 196 DUG 117 200 N15A 94 201 P10A 221 206 SPU 81 208 M15A 76 211 K11A 334 215 O09A 244 217 M09A 282 218 K14A 40 220 N09A 266 222 O15A 111 222 Q12A 178 222 L15A 62 236 NOQ 99 238 Q13A 162 243 J12A 356 246 P09A 230 252 Q11A 195 252 K10A 320 253 L09A 296 256 Q14A 148 266 CTU 97 268 NLU 116 268 J13A 13 269 K15A 46 269 N08A 265 274 J11A 344 275 M16A 82 276 P15A 125 276 Q10A 208 277 J14A 24 278 HLID 8 283 O08A 254 288 N16A 92 292 M08A 280 295 K09A 309 299 MPU 111 299 R12A 175 302 R11A 191 304 J10A 330 307 L16A 68 309 Q15A 136 312 Q09A 219 313 L08A 295 315 P16A 119 317 I13A 11 326 R13A 166 327 R10A 202 328 I11A 345 331 J15A 37 332 K16A 53 339 N17A 90 342 I14A 20 343 N07B 267 344 R14A 152 344 WVOR 298 348 J09A 318 349 O07A 255 351 K08A 304 352 Q08A 228 354 L17A 69 356 M17A 81 358 M07A 278 361 R09A 212 362 O17A 104 364 J16A 46 368 AHID 57 369 TMU 120 369 I10A 336 373 S10A 204 375 P07A 245 378 K17A 59 381 S12A 179 381 I15A 30 384 S11A 191 384 L07A 288 386 R15A 144 386 H12A 0 390 RRI2 48 391 J08A 312 392 S14A 157 393 P17A 115 394 S13A 167 394 H13A 7 395 Q16A 125 396 I09A 325 401 K07A 298 405 R08A 224 406 M18A 82 407 CCUT 161 409 H11A 348 417 N06A 267 417 DCID1 46 418 L18A 75 418 S09A 209 419 I16A 40 422 O18A 100 422 REDW 51 422 T11A 184 422 H10A 340 423 R16A 135 423 P18A 110 425 TPAW 49 425 O06A 259 428 SRU 118 430 J17A 52 432 S15A 149 432 SNOW 50 435 H15A 24 438 I08A 318 439 K18A 65 441 J07A 307 447 P06A 252 451 G13A 7 454 T13A 169 454 IMW 44 455 LOHW 50 455 Q18A 116 460 H09A 332 462 R17A 128 462 BMO 336 467 T14A 160 468 J18A 58 470 L19A 74 477 I17A 46 478 T12A 178 479 R06C 236 480 G14A 14 482 N19A 90 482 BW06 65 483 M19A 82 484 H08A 323 495 O19A 98 495 T15A 153 496 G15A 22 499 J06A 301 499 H16A 35 505 G10A 340 506 I07A 313 507 I18A 53 512 U12A 176 512 U11A 185 514 DLMT 20 516 S17A 136 517 U13A 171 519 R18A 123 520 F12A 357 525 G09A 334 526 P19A 105 526 U10A 194 527 G16A 27 529 K05A 293 532 Q19A 114 534 U14A 163 534 T16A 146 537 K19A 66 540 I06A 308 543 F14A 13 545 F11A 350 549 L20A 77 558 N20A 90 559 S18A 130 562 M20A 83 564 F15A 19 568 R19A 120 571 T17A 140 571 O20A 98 572 G08A 326 576 BOZ 26 577 P20A 105 579 V11A 185 579 F10A 342 580 V13A 172 581 G17A 34 584 V12A 180 589 F16A 26 590 E11A 350 600 E13A 5 603 H06A 315 605 E14A 10 608 G07A 322 609 Q20A 110 609 T18A 133 613 U17A 142 614 F08A 331 615 S19A 124 616 V14A 165 620 N21A 90 622 E15A 16 626 V15A 157 626 E10A 344 631 M21A 82 634 U16A 148 634 O21A 96 635 L21A 78 637 W12A 180 637 F17A 31 640 G18A 41 643 R20A 117 643 RLMT 43 645 MSO 6 648 LDF 182 656 GSC 195 658 G06A 317 660 E09A 338 662 E16A 22 663 W13A 172 665 W14A 166 666 Q21A 109 672 ISA 209 673 U18A 138 673 D13A 3 674 F07A 325 676 D11A 351 678 D14A 9 681 E17A 27 685 W15A 160 690 T19A 131 691 HUMO 287 692 D10A 345 695 M22A 84 697 G05A 314 700 HAWA 330 702 LTH 330 704 F06A 320 709 N22A 89 711 D16A 21 718 H04A 307 720 X13A 172 721 W16A 155 722 D09A 339 723 Q22A 107 724 E07A 329 732 E18A 31 733 V18A 142 733 C13A 2 739 SAO 232 740 D08A 336 742 C12B 357 743 X14A 166 750 MCCM 248 757 D17A 25 758 X15A 161 764 R22A 111 765 C15A 13 771 G04A 309 771 C10A 346 778 V19A 137 781 E06A 323 783 OSI 206 788 C16A 17 792 COR 303 792 PHWY 85 792 D07A 331 795 X16A 156 795 W18A 144 797 C09A 342 798 ISCO 97 799 C17A 23 803 Y14A 167 805 MWC 201 806 Y13A 173 807 Y12C 178 809 B13A 2 816 W19A 142 816 Y15A 163 818 C08A 338 819 NEW 348 822 T22A 120 823 X17A 153 826 B10A 348 828 B12A 356 828 B15A 12 829 B11A 352 831 D06A 327 833 X18A 147 843 C07A 333 846 Y16A 158 850 B16A 16 858 B09A 344 860 W20A 137 863 B17A 20 869 Z14A 168 869 EGMT 26 877 Z13A 172 877 A13A 2 878 A12A 356 880 B08A 338 886 F03A 311 886 GLA 180 886 SDCO 111 887 A11A 353 888 D05A 323 888 A14A 7 890 Y17A 155 890 Z15A 163 893 C06A 330 901 A10A 348 907 Z16A 159 908 B18A 25 912 W21A 134 914 B07A 335 922 113A 173 923 109C 193 925 D04A 320 925 E03A 314 927 A09A 343 929 Y19A 146 930 114A 168 937 LAO 45 937 112A 178 944 Z17A 154 944 RSSD 65 954 115A 165 955 SNCC 207 957 A18A 23 962 W22A 131 966 B06A 330 981 116A 162 982 Z18A 152 982 A07A 336 989 Z19A 148 994 ANMO 130 1002 X22A 134 1003 117A 157 1010 214A 169 1025 TUC 158 1035 119A 150 1044 Y22D 135 1044 216A 162 1048 A05A 330 1050 OGNE 86 1082 217A 159 1091 120A 147 1095 218A 155 1095 121A 144 1136 122A 140 1161 220A 149 1162 DGMT 42 1181 319A 153 1184 221A 145 1186 222A 142 1211 CBKS 96 1317 324A 140 1342 AMTX 116 1345 ECSD 73 1532 KSU1 92 1572 WMOK 111 1577 EYMN 60 2004 MIAR 104 2005 CCM 248 2053 UALR 102 2094 HKT 120 2113 FVM 91 2124 COWI 66 2145 HDIL 83 2154 KVTX 129 2158 OLIL 88 2297 OXF 100 2349 USIN 89 2357 VBMS 106 2379 BLO 86 2418 PLAL 97 2438 WCI 88 2464 GLMI 70 2492 AAM 76 2591 BRAL 105 2721 TZTN 90 2753 GOGA 97 2897 BLA 87 2992
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:
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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 0.10 n 3
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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.
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.
The WUS.REG 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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Thu Feb 28 16:03:15 CST 2008