2007/08/06 05:59:45 37.811 -114.433 5.0 4.1 Nevada
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2007/08/06 05:59:45 37.811 -114.433 5.0 4.1 Nevada
Best Fitting Double Couple
Mo = 8.04e+21 dyne-cm
Mw = 3.87
Z = 8 km
Plane Strike Dip Rake
NP1 14 82 145
NP2 110 55 10
Principal Axes:
Axis Value Plunge Azimuth
T 8.04e+21 30 326
N 0.00e+00 54 183
P -8.04e+21 18 67
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.01e+21
Mxy -5.39e+21
Mxz 2.00e+21
Myy -4.32e+21
Myz -4.10e+21
Mzz 1.31e+21
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##### ############----------
####### T ############------------
######## ###########--------------
#######################---------- --
-#######################---------- P ---
-######################----------- ---
---#####################------------------
-----##################-------------------
------#################-------------------
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Harvard Convention
Moment Tensor:
R T F
1.31e+21 2.00e+21 4.10e+21
2.00e+21 3.01e+21 5.39e+21
4.10e+21 5.39e+21 -4.32e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20070806055945/index.html
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STK = 110
DIP = 55
RAKE = 10
MW = 3.87
HS = 8
The two techniques give similar solutiosn. The waveforms inversion is preferred.
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 3 br c 0.12 0.25 n 4 p 2The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 105 65 -25 3.59 0.3772
WVFGRD96 1.0 110 80 -10 3.58 0.3973
WVFGRD96 2.0 105 65 -25 3.72 0.4859
WVFGRD96 3.0 105 60 -15 3.75 0.5062
WVFGRD96 4.0 110 60 0 3.77 0.5184
WVFGRD96 5.0 110 60 5 3.79 0.5284
WVFGRD96 6.0 110 60 10 3.81 0.5374
WVFGRD96 7.0 110 60 10 3.83 0.5421
WVFGRD96 8.0 110 55 10 3.87 0.5433
WVFGRD96 9.0 110 60 5 3.87 0.5420
WVFGRD96 10.0 110 60 5 3.88 0.5396
WVFGRD96 11.0 110 65 5 3.89 0.5351
WVFGRD96 12.0 110 65 5 3.90 0.5301
WVFGRD96 13.0 110 65 0 3.91 0.5228
WVFGRD96 14.0 110 65 0 3.92 0.5143
WVFGRD96 15.0 290 65 -5 3.93 0.5062
WVFGRD96 16.0 290 65 -5 3.94 0.4986
WVFGRD96 17.0 290 70 -5 3.95 0.4894
WVFGRD96 18.0 290 70 -5 3.96 0.4805
WVFGRD96 19.0 290 70 -5 3.97 0.4697
WVFGRD96 20.0 290 70 -5 3.98 0.4586
WVFGRD96 21.0 290 65 -5 3.98 0.4477
WVFGRD96 22.0 290 65 -5 3.99 0.4364
WVFGRD96 23.0 290 65 -5 4.00 0.4246
WVFGRD96 24.0 290 65 -5 4.00 0.4135
WVFGRD96 25.0 290 65 -5 4.01 0.4013
WVFGRD96 26.0 290 60 -5 4.02 0.3885
WVFGRD96 27.0 290 65 -5 4.02 0.3768
WVFGRD96 28.0 20 85 -15 4.02 0.3721
WVFGRD96 29.0 20 85 -15 4.03 0.3695
The best solution is
WVFGRD96 8.0 110 55 10 3.87 0.5433
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 br c 0.12 0.25 n 4 p 2
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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= 12.36
DIP= 77.05
RAKE= 149.13
OR
STK= 109.99
DIP= 60.00
RAKE= 15.00
DEPTH = 10.0 km
Mw = 3.97
Best Fit 0.9239 - 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
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) Q13A 12 135 U12A 187 149 Q14A 34 165 Q11A 317 166 S15A 92 174 U11A 212 175 U14A 145 181 R10A 289 182 R15A 74 188 P13A 8 190 T15A 115 192 TPNV 242 192 P12A 346 196 S10A 276 199 V13A 171 214 Q10A 304 215 Q15A 51 220 V12A 192 230 P14A 28 231 U10A 230 231 P11A 329 234 U15A 128 235 V11A 205 235 R09A 283 246 S09A 270 254 V14A 155 261 O13A 7 265 T16A 108 265 P15A 41 269 Q09A 296 276 P10A 319 277 W12A 190 277 O12A 353 280 O11A 337 287 V15A 138 290 W13A 172 298 DUG 26 301 W14A 158 304 Q16A 64 305 LDF 193 306 P16A 48 310 S17A 92 312 P09A 310 314 O15A 30 323 T17A 104 324 R17A 76 326 O10A 327 337 Q08A 292 337 R08A 282 337 S08C 266 339 ELK 347 340 W15A 146 342 N13A 2 344 N12A 350 348 GSC 220 351 U17A 110 351 X13A 172 355 N14A 16 357 N11A 341 360 O09A 318 364 WUAZ 132 364 O16A 41 366 P17A 58 366 N10A 331 378 N15A 24 381 S18A 90 383 W16A 139 388 X14A 160 388 P08A 305 390 Q18A 67 396 R18A 79 396 M13A 2 400 T18A 99 401 M12A 353 409 X15A 152 410 P18A 59 412 Q07A 290 412 R07C 276 415 M14A 11 424 U18A 109 424 M11A 343 426 N16A 35 428 HELL 255 433 O08A 312 433 ISA 239 437 N09A 322 439 Y13A 174 440 W17A 131 441 Y14A 164 441 M15A 21 442 P07A 298 442 Y12C 182 445 R19A 81 450 X16A 144 454 V18A 119 455 R06C 282 456 M10A 336 458 M16A 30 458 S19A 89 458 Y15A 156 460 Q19A 72 463 N17A 40 465 O18A 52 467 N08A 317 468 O07A 306 475 L13A 4 482 T19A 101 482 T06C 262 483 L14A 11 484 S06C 273 485 M09A 328 486 L12A 353 490 X17A 139 496 L15A 19 500 WCN 292 502 Y16A 148 502 L11A 347 504 Z14A 165 504 W18A 124 506 L10A 340 513 R05C 284 513 MWC 222 516 MVCO 95 520 N07B 311 521 GLA 185 524 V19A 114 524 P06A 296 528 S05C 267 531 W19A 122 532 CMB 275 533 X18A 131 533 L16A 27 534 Z15A 158 534 M08A 321 536 N18A 47 537 U05C 255 538 K14A 10 540 K12A 355 543 K13A 2 543 O06A 301 545 Y17A 144 551 L09A 330 552 113A 174 556 Z16A 151 557 LAVA 283 571 BEK 296 572 P05C 289 573 K11A 346 575 M07A 316 578 N06A 307 579 112A 182 580 R04C 277 582 X19A 128 586 Y18A 137 589 109C 206 596 K10A 340 597 L08A 326 599 BAR 201 602 Z17A 144 607 K16A 22 610 J12A 354 613 S04C 270 617 K09A 333 619 AHID 25 620 O05C 295 621 Y19A 131 624 116A 157 625 J13A 1 626 Q04C 283 627 WVOR 326 635 ELFS 302 636 L07A 319 637 J11A 349 640 SAO 262 640 HLID 360 644 V03C 255 644 O04C 298 649 Z18A 142 649 M06C 308 652 K08A 329 655 214A 167 659 HAST 259 659 J10A 343 662 117A 149 663 SUTB 286 670 Q03C 280 679 I13A 2 684 J09A 336 684 MOD 314 687 BW06 35 688 K07A 324 688 REDW 24 688 216A 157 691 118A 144 694 I11A 349 696 BNLO 267 697 HATC 301 701 M05C 306 708 O03C 293 712 J08A 332 713 119A 139 719 L05A 313 731 MOOW 23 731 I10A 344 732 217A 153 738 I09A 338 747 RWWY 52 750 218A 147 752 J07A 328 752 K06A 320 752 MCCM 276 752 H12A 357 755 H13A 0 755 I08A 334 770 M03C 303 774 HOPS 283 775 O02C 293 779 M04C 307 782 J06A 323 783 H11A 350 784 K05A 317 784 Y22C 119 784 H10A 346 785 219A 142 790 ISCO 71 791 P01C 286 806 318A 149 807 L04A 310 810 G13A 1 814 H09A 341 816 I07A 330 825 BMO 344 826 K04A 313 828 G14A 5 834 H08A 336 834 M02C 302 835 G15A 10 837 YBH 304 841 N02C 296 844 I06A 326 846 319A 145 847 J05A 319 847 G11A 350 863 O01C 291 863 G10A 345 868 H07A 332 876 G09A 342 883 F12A 355 891 F13A 0 892 J04A 315 896 F14A 5 898 HUMO 309 909 F15A 9 910 F11A 351 915 I05A 323 919 G08A 337 920 RLMT 26 920 H06A 329 923 L02A 305 929 F09A 343 931 F10A 346 943 G07A 334 944 M01C 302 952 I04A 317 955 K02A 308 955 H05A 325 958 E13A 1 964 E14A 4 964 F08A 339 965 E11A 351 967 E15A 8 972 G06A 330 982 E10A 348 995 J02A 311 998 MSO 2 1008 H04A 322 1011 G05A 327 1014 F07A 335 1015 I03A 315 1020 E09A 343 1021 D13A 360 1037 D14A 4 1037 F06A 331 1037 D15A 8 1042 D11A 352 1044 E08A 340 1045 HAWA 338 1050 I02A 314 1057 D10A 348 1060 MNTX 127 1060 H03A 318 1073 E07A 337 1077 F05A 329 1078 D09A 344 1083 D08A 341 1099 C13A 359 1102 C14A 2 1113 H02A 317 1115 E06A 333 1118 G03A 321 1121 F04A 326 1127 C10A 349 1143 E05A 330 1153 C09A 345 1160 D06A 335 1175 C08A 342 1178 B13A 360 1179 AMTX 102 1180 F03A 323 1186 NEW 350 1188 B10A 350 1194 B12A 356 1194 LAO 31 1195 B11A 353 1197 C07A 339 1197 E04A 328 1199 EGMT 17 1199 D05A 332 1220 B09A 347 1224 E03A 325 1236 A13A 360 1241 B08A 343 1245 A12A 356 1246 C06A 337 1248 D04A 329 1249 A11A 353 1254 C05A 334 1256 A10A 349 1273 B07A 340 1277 CBKS 80 1281 A09A 346 1292 D03A 326 1295 A08A 344 1305 C04A 330 1311 NLWA 327 1323 B05A 334 1325 B06A 336 1327 A07A 341 1345 B04A 330 1365 A06A 338 1384 A04A 334 1392 A05A 336 1396 WMOK 99 1436 DGMT 31 1445 KSU1 79 1553 JCT 117 1563 ECSD 60 1633 SCIA 69 1861 MIAR 95 1898 AGMN 46 1899 NATX 104 1916 FVM 82 2098 SLM 80 2107 JFWS 67 2117 EYMN 51 2171 HDIL 74 2179 PVMO 86 2189 MPH 90 2201 SIUC 82 2208 VBMS 99 2253 OXF 92 2266 OLIL 79 2292 USIN 81 2339 PLAL 90 2369 BLO 78 2423 BRAL 98 2608 AAM 69 2652 TZTN 83 2726 BLA 81 2984 NHSC 89 3127 PAL 71 3471 LBNH 65 3599
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 br c 0.12 0.25 n 4 p 2
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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
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Sat Aug 25 15:55:21 CDT 2007