2006/06/30 16:55:01 42.432 -111.501 1. 4.3 Idaho
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution
2006/06/30 16:55:01 42.432 -111.501 1. 4.3 Idaho
Best Fitting Double Couple
Mo = 2.11e+22 dyne-cm
Mw = 4.15
Z = 10 km
Plane Strike Dip Rake
NP1 10 65 -70
NP2 149 32 -126
Principal Axes:
Axis Value Plunge Azimuth
T 2.11e+22 18 85
N 0.00e+00 18 181
P -2.11e+22 64 314
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.78e+21
Mxy 3.55e+21
Mxz -5.23e+21
Myy 1.70e+22
Myz 1.20e+22
Mzz -1.52e+22
-----------###
----------------######
##------------------########
##-------------------#########
###---------------------##########
###----------------------###########
####----------------------############
####---------- ----------#############
####---------- P ----------#############
#####---------- ----------######### ##
######----------------------######### T ##
######---------------------########## ##
#######--------------------###############
######-------------------###############
#######------------------###############
#######----------------###############
########--------------##############
########------------##############
########---------#############
##########-----#############
##########--##########
#####---------
Harvard Convention
Moment Tensor:
R T F
-1.52e+22 -5.23e+21 -1.20e+22
-5.23e+21 -1.78e+21 -3.55e+21
-1.20e+22 -3.55e+21 1.70e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20060630165501/index.html
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The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
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STK = 10
DIP = 65
RAKE = -70
MW = 4.15
HS = 10
The waveform inversion is preferred. The surface-wave inversion agrees with it.
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 0.5 350 45 85 3.76 0.3712
WVFGRD96 1.0 50 85 0 3.72 0.3573
WVFGRD96 2.0 50 75 -5 3.82 0.3898
WVFGRD96 3.0 45 50 10 3.88 0.4397
WVFGRD96 4.0 45 50 15 3.91 0.4940
WVFGRD96 5.0 45 50 20 3.94 0.5261
WVFGRD96 6.0 220 55 10 3.96 0.5486
WVFGRD96 7.0 10 70 -75 4.07 0.5836
WVFGRD96 8.0 360 65 -80 4.10 0.6082
WVFGRD96 9.0 360 65 -75 4.12 0.6221
WVFGRD96 10.0 10 65 -70 4.15 0.6265
WVFGRD96 11.0 10 65 -70 4.16 0.6205
WVFGRD96 12.0 10 65 -65 4.16 0.6083
WVFGRD96 13.0 10 65 -65 4.17 0.5884
WVFGRD96 14.0 10 65 -60 4.17 0.5638
WVFGRD96 15.0 10 65 -60 4.17 0.5362
WVFGRD96 16.0 10 65 -55 4.17 0.5071
WVFGRD96 17.0 10 65 -55 4.17 0.4772
WVFGRD96 18.0 195 70 -50 4.20 0.4494
WVFGRD96 19.0 195 70 -50 4.20 0.4232
WVFGRD96 20.0 205 75 75 4.22 0.4100
WVFGRD96 21.0 205 75 80 4.29 0.3955
WVFGRD96 22.0 200 75 80 4.29 0.3795
WVFGRD96 23.0 200 75 80 4.30 0.3632
WVFGRD96 24.0 200 75 80 4.30 0.3464
WVFGRD96 25.0 120 25 20 4.25 0.3309
WVFGRD96 26.0 125 25 25 4.26 0.3261
WVFGRD96 27.0 125 25 25 4.26 0.3213
WVFGRD96 28.0 125 25 25 4.27 0.3157
WVFGRD96 29.0 125 25 25 4.28 0.3109
The best solution is
WVFGRD96 10.0 10 65 -70 4.15 0.6265
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. |
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NODAL PLANES
STK= 8.94
DIP= 65.82
RAKE= -71.68
OR
STK= 150.00
DIP= 30.00
RAKE= -124.99
DEPTH = 10.0 km
Mw = 4.16
Best Fit 0.9025 - 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 AHID 41 50 iP_C HWUT 183 92 eP_+ REDW 27 116 eP_+ SNOW 28 130 iP_C LOHW 29 150 iP_C MOOW 23 159 iP_C BW06 76 164 eP_+ M13A 243 251 iP_D LKWY 20 253 eP_X HLID 299 269 iP_D DUG 204 272 iP_D M12A 249 305 eP_X BOZ 358 358 eP_- ELK 240 364 eP_X RWWY 102 365 iP_C SRU 167 378 eP_X N11A 244 396 eP_X O11A 235 432 iP_D MVU 188 440 iP_D Q12A 218 470 eP_- P11A 230 480 eP_X O10A 242 481 eP_X M09A 259 506 eP_X L09A 267 511 eP_X PHWY 102 517 iP_C Q11A 223 531 iP_D O09A 244 539 iP_D TPNV 215 733 eP_X WUAZ 179 768 eP_X
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.
The velocity model used for the search is a modified Utah model .
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. |
Sta Az(deg) Dist(km) HWUT 183 92 REDW 27 116 SNOW 28 130 LOHW 29 150 MOOW 23 159 BW06 76 164 M13A 243 251 HLID 299 269 DUG 204 272 M12A 249 305 BOZ 358 358 ELK 240 364 RWWY 102 365 SRU 167 378 N11A 244 396 O11A 235 432 MVU 188 440 Q12A 218 470 P11A 230 480 O10A 242 481 M09A 259 506 L09A 267 511 PHWY 102 517 Q11A 223 531 O09A 244 539 ISCO 119 574 K08A 276 574 J08A 283 579 WVOR 272 587 O08A 249 605 Q09A 232 625 P08A 243 631 K07A 275 637 Q08A 236 673 S09A 225 715 U12A 202 716 K06A 276 719 I06A 286 728 TPNV 215 733 U11A 208 746 WUAZ 179 768 L05A 270 771 HAWA 307 776 U10A 214 786 V12A 202 799 R06C 240 801 W14A 190 813 H05A 291 824 O05C 254 836 W12A 201 844 S06C 237 872 X15A 184 884 X14A 188 892 H04A 290 899 O03C 256 923 G04A 293 935 S05C 236 942 M02C 267 949 Y14A 188 952 F04A 298 955 Y13A 193 978 D05A 306 983 J02A 280 991 L02A 272 998 N02C 264 999 S04C 240 1001 U05C 230 1004 Z14A 188 1015 D04A 304 1034 M01C 271 1045 U04C 233 1045 P01C 256 1049 O01C 260 1062 116A 181 1096 ECSD 78 1221 JCT 138 1687 SLM 96 1846 FVM 98 1856 UALR 111 1867 PVMO 102 1986 MPH 106 2035 USIN 96 2082 BLO 91 2131 PLAL 104 2190 AAM 81 2284 ACSO 86 2389
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 velocity model used for the waveform fit is a modified Utah model .
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
this solution was made possible by the use of wavefroms from the University of Utah Seismograph Network
The figures below show the observed spectral amplitudes (units of cm-sec) at each station and the
theoretical predictions as a function of period for the mechanism given above. The modified Utah model earth model
was used to define the Green's functions. For each station, the Love and Rayleigh wave spectrail amplitudes are plotted with the same scaling so that one can get a sense fo the effects of the effects of the focal mechanism and depth on the excitation of each.
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Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
