2008/04/01 13:16:17 41.224 -114.826 7.6 4.2 Nevada
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/04/01 13:16:17 41.224 -114.826 7.6 4.2 Nevada
Best Fitting Double Couple
Mo = 1.91e+22 dyne-cm
Mw = 4.12
Z = 12 km
Plane Strike Dip Rake
NP1 185 79 -139
NP2 85 50 -15
Principal Axes:
Axis Value Plunge Azimuth
T 1.91e+22 18 309
N 0.00e+00 48 198
P -1.91e+22 36 53
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.37e+21
Mxy -1.43e+22
Mxz -1.88e+21
Myy 2.49e+21
Myz -1.17e+22
Mzz -4.86e+21
########------
###########-----------
##############--------------
##############----------------
## ###########------------------
### T ##########----------- ------
#### ##########----------- P -------
##################----------- --------
##################----------------------
##################------------------------
##################-----------------------#
##################----------------------##
-#################--------------------####
--###############------------------#####
----#############----------------#######
-------#########------------##########
---------------#####################
--------------####################
------------##################
-----------#################
---------#############
-----#########
Harvard Convention
Moment Tensor:
R T F
-4.86e+21 -1.88e+21 1.17e+22
-1.88e+21 2.37e+21 1.43e+22
1.17e+22 1.43e+22 2.49e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080401131617/index.html
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STK = 85
DIP = 50
RAKE = -15
MW = 4.12
HS = 12.0
Good fits are obtained with the two techniques. The southward dipping nodal plane striking East is common to both. The waveform solution fits the surface-wave radiations patterns slightly less than the surface-wave solution. On the other hand the surface wave solution can provide an acceptable fit to the waveforms. The difference between the goodness of fit parameter for the best waveform solutiona nd the surface-wave solution is about 0.03, which is not significant. We accept the waveform solution here. Using a sligltly lower frequency band for the waveform search might reconcile the slight differences.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/04/01 13:16:17 41.224 -114.826 7.6 4.2 Nevada
Best Fitting Double Couple
Mo = 1.91e+22 dyne-cm
Mw = 4.12
Z = 12 km
Plane Strike Dip Rake
NP1 185 79 -139
NP2 85 50 -15
Principal Axes:
Axis Value Plunge Azimuth
T 1.91e+22 18 309
N 0.00e+00 48 198
P -1.91e+22 36 53
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.37e+21
Mxy -1.43e+22
Mxz -1.88e+21
Myy 2.49e+21
Myz -1.17e+22
Mzz -4.86e+21
########------
###########-----------
##############--------------
##############----------------
## ###########------------------
### T ##########----------- ------
#### ##########----------- P -------
##################----------- --------
##################----------------------
##################------------------------
##################-----------------------#
##################----------------------##
-#################--------------------####
--###############------------------#####
----#############----------------#######
-------#########------------##########
---------------#####################
--------------####################
------------##################
-----------#################
---------#############
-----#########
Harvard Convention
Moment Tensor:
R T F
-4.86e+21 -1.88e+21 1.17e+22
-1.88e+21 2.37e+21 1.43e+22
1.17e+22 1.43e+22 2.49e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080401131617/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 0.5 215 45 -90 3.69 0.2912
WVFGRD96 1.0 250 55 -40 3.68 0.2575
WVFGRD96 2.0 225 45 -75 3.87 0.3401
WVFGRD96 3.0 260 55 -20 3.85 0.3402
WVFGRD96 4.0 95 45 15 3.91 0.3877
WVFGRD96 5.0 95 45 15 3.94 0.4329
WVFGRD96 6.0 95 50 15 3.96 0.4718
WVFGRD96 7.0 90 55 15 3.99 0.5047
WVFGRD96 8.0 80 40 -25 4.06 0.5409
WVFGRD96 9.0 85 45 -15 4.07 0.5616
WVFGRD96 10.0 85 50 -15 4.09 0.5753
WVFGRD96 11.0 85 50 -15 4.11 0.5830
WVFGRD96 12.0 85 50 -15 4.12 0.5842
WVFGRD96 14.0 85 55 -15 4.15 0.5649
WVFGRD96 15.0 85 55 -15 4.16 0.5542
WVFGRD96 16.0 85 55 -15 4.17 0.5402
WVFGRD96 17.0 85 55 -15 4.18 0.5238
WVFGRD96 18.0 85 55 -15 4.19 0.5059
WVFGRD96 19.0 85 55 -15 4.20 0.4866
WVFGRD96 20.0 85 55 -15 4.20 0.4667
WVFGRD96 21.0 85 55 -15 4.21 0.4474
WVFGRD96 22.0 85 55 -15 4.22 0.4274
WVFGRD96 23.0 85 55 -10 4.22 0.4077
WVFGRD96 24.0 85 55 -10 4.23 0.3887
WVFGRD96 25.0 85 55 -10 4.23 0.3700
WVFGRD96 26.0 85 55 -10 4.23 0.3519
WVFGRD96 27.0 85 55 -10 4.24 0.3346
WVFGRD96 28.0 85 55 -10 4.24 0.3183
WVFGRD96 29.0 85 55 -10 4.24 0.3031
WVFGRD96 13.0 85 55 -15 4.14 0.5811
The best solution is
WVFGRD96 12.0 85 50 -15 4.12 0.5842
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= 344.64
DIP= 67.48
RAKE= 135.90
OR
STK= 94.99
DIP= 50.00
RAKE= 30.00
DEPTH = 9.0 km
Mw = 4.17
Best Fit 0.9105 - 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) M10A 284 142 HVU 67 180 SPU 85 195 K11A 331 196 DUG 122 198 P11A 202 200 N15A 100 202 K14A 44 204 M15A 82 206 P13A 159 210 M09A 277 216 P10A 217 223 L15A 67 226 O15A 116 229 NOQ 103 231 K10A 317 238 P14A 139 238 Q12A 179 243 L09A 292 248 K15A 50 254 J11A 343 255 J14A 25 259 CTU 101 260 Q13A 163 263 NLU 120 265 HLID 6 268 Q11A 194 272 HWUT 79 273 Q14A 151 284 K09A 306 287 P15A 129 288 J10A 328 290 N16A 96 292 M08A 276 293 MPU 115 295 Q10A 206 296 L16A 72 301 I13A 12 305 L08A 292 307 O16A 110 307 I11A 344 311 J15A 39 315 I14A 21 323 R12A 176 323 R11A 191 325 K16A 56 326 P16A 122 327 Q15A 138 327 J09A 316 334 K08A 300 342 N17A 94 342 R13A 167 347 L17A 72 348 R10A 201 348 WVOR 295 351 AHID 58 352 M17A 84 354 I10A 334 355 M07A 274 359 R14A 153 362 I15A 32 366 H12A 0 369 O17A 107 369 K17A 61 370 RRI2 48 374 H13A 8 375 J08A 310 379 L07A 285 381 I09A 324 385 S10A 202 395 K07A 296 396 H11A 347 397 H14A 18 397 DCID1 46 400 P17A 118 402 S12A 180 402 H10A 338 403 R15A 145 403 M18A 85 404 S11A 191 404 REDW 52 405 I16A 42 406 Q16A 128 407 TPAW 49 407 L18A 78 412 S14A 158 412 S13A 167 414 J17A 54 418 SNOW 51 418 CCUT 163 419 H15A 25 419 N06A 264 420 I08A 316 425 O18A 103 425 SRU 121 428 K18A 67 431 G13A 7 433 J07A 305 436 IMW 45 437 LOHW 50 438 R16A 137 438 N18A 92 439 T11A 184 443 H09A 330 444 J18A 60 458 BMO 334 459 G14A 14 461 I17A 48 463 BW06 66 467 Q18A 119 468 L19A 76 471 R17A 130 474 T13A 169 474 G11A 347 477 G15A 23 479 H08A 321 479 M19A 84 480 N19A 92 481 G10A 339 487 H16A 36 487 T14A 161 488 J06A 299 489 I07A 312 494 O19A 100 497 DLMT 20 499 I18A 55 499 T12A 178 500 F12A 357 504 G09A 333 508 F13A 5 509 G16A 28 510 T15A 154 515 LKWY 42 520 F14A 13 524 K05A 290 525 F11A 349 528 K19A 68 531 P19A 108 531 R18A 125 531 S17A 137 531 U12A 177 533 U11A 185 535 U13A 171 540 Q19A 116 542 F15A 20 548 U10A 194 548 L20A 79 552 T16A 147 554 U14A 164 554 F09A 335 555 BOZ 26 559 N20A 92 559 F10A 341 560 G08A 325 560 M20A 85 561 K20A 72 565 G17A 35 566 F16A 26 571 O20A 100 574 S18A 131 575 U15A 156 578 E11A 350 580 E13A 5 582 R19A 122 582 P20A 107 584 T17A 142 587 E14A 10 588 H06A 313 591 F08A 330 597 V11A 185 600 E15A 17 605 V12A 180 610 E10A 344 611 Q20A 112 616 F17A 32 622 N21A 92 622 G18A 42 627 RLMT 44 627 S19A 126 627 T18A 135 627 M21A 84 630 U17A 143 631 L21A 80 632 MSO 6 633 RWWY 82 635 O21A 98 636 V14A 165 640 E09A 337 643 E16A 22 644 G06A 316 645 V15A 158 645 R20A 119 652 U16A 149 652 D13A 3 653 D11A 350 657 W12A 180 658 P21A 104 659 D14A 9 660 E17A 28 666 F18A 37 667 LDF 183 671 D15A 16 673 D10A 344 675 GSC 196 675 Q21A 111 678 W13A 172 686 W14A 166 686 U18A 139 688 ISA 209 691 M22A 86 694 WUAZ 154 694 HAWA 328 695 LTH 329 697 MVCO 127 697 D16A 21 698 HUMO 286 698 SMCO 106 700 R21A 114 703 D09A 338 704 T19A 132 704 H04A 305 708 W15A 160 709 E07A 328 714 E18A 32 715 V17A 149 717 C13A 2 718 C12B 356 722 D08A 335 724 S21A 121 727 Q22A 108 729 C14A 7 733 U19A 136 737 D17A 26 739 W16A 156 741 X13A 172 742 V18A 143 749 C15A 13 750 SAO 232 757 C10A 346 758 G04A 308 759 E06A 322 767 X14A 166 770 U20A 132 771 C16A 18 772 MCCM 247 772 R22A 113 772 D07A 330 778 D18A 30 778 C09A 341 779 PHWY 86 781 X15A 162 783 C17A 23 784 ISCO 98 791 COR 301 793 V19A 138 796 C08A 337 800 F04A 313 802 OSI 207 806 B12A 356 807 B10A 348 808 B15A 12 809 B11A 352 810 NEW 348 810 W18A 145 814 X16A 157 814 V20A 135 822 MWC 202 823 Y14A 168 826 C07A 332 828 Y13A 173 828 Y12C 178 830 W19A 143 832 T22A 122 833 B16A 16 837 Y15A 164 838 B09A 343 840 X17A 154 845 B17A 21 849 A12A 356 859 EGMT 26 860 X18A 148 860 A11A 353 867 B08A 338 867 A14A 7 869 Y16A 159 869 D05A 322 872 V21A 131 872 F03A 310 873 A15A 10 878 W20A 138 878 SDCO 112 883 C06A 329 884 A10A 347 887 Z14A 168 889 B18A 25 893 A16A 16 896 Z13A 173 897 GLA 180 901 X19A 145 901 B07A 335 904 A09A 343 909 Y17A 156 909 E03A 313 913 Z15A 164 913 A17A 20 919 A08A 340 925 Z16A 160 927 W21A 135 928 X20A 141 930 RSSD 66 939 113A 174 944 109C 193 946 Y19A 147 947 114A 169 957 B06A 330 963 Z17A 155 963 112A 178 965 A07A 336 970 SNCC 207 974 X21A 138 977 W22A 132 979 Y20A 143 994 Z18A 153 1000 116A 163 1002 ANMO 131 1004 Z19A 149 1011 Y21A 139 1022 117A 158 1029 A05A 329 1032 214A 169 1045 TUC 159 1045 Y22D 136 1059 Z20A 146 1059 119A 150 1062 216A 162 1068 OGNE 87 1070 Z21A 142 1086 217A 160 1110 120A 148 1112 218A 156 1114 121A 144 1153 DGMT 42 1164 318A 156 1171 122A 141 1177 220A 149 1180 221A 146 1203 319A 154 1203 222A 143 1227 320A 151 1236 223A 141 1271 CBKS 97 1309 224A 138 1314 125A 133 1315 AMTX 117 1342 MNTX 138 1345 225A 135 1352 126A 131 1356 324A 139 1373 127A 129 1396 226A 133 1399 325A 138 1408 326A 135 1470 327A 133 1495 ECSD 73 1518 426A 137 1524 427A 134 1545 KSU1 92 1562 WMOK 112 1573 526A 138 1575 527A 137 1595 428A 133 1599 626A 140 1619 528A 135 1642 627A 138 1670 JCT 127 1794 MIAR 105 1998 JFWS 76 2033 CCM 247 2043 NATX 114 2076 HKT 120 2112 HDIL 83 2142 KVTX 129 2159 OXF 100 2342 WCI 88 2453 TZTN 90 2743 GOGA 97 2888
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 VMODEL 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=Wed Apr 2 13:17:47 CDT 2008