USGS Felt map for this earthquake
SLU Moment Tensor Solution
Best Fitting Double Couple
Mo = 5.62e+23 dyne-cm
Mw = 5.10
Z = 10 km
Plane Strike Dip Rake
NP1 349 47 -105
NP2 190 45 -75
Principal Axes:
Axis Value Plunge Azimuth
T 5.62e+23 1 89
N 0.00e+00 11 359
P -5.62e+23 79 185
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.88e+22
Mxy 3.82e+21
Mxz 1.01e+23
Myy 5.62e+23
Myz 1.79e+22
Mzz -5.43e+23
######--######
#########----#########
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#########-----------##########
##########--------------##########
##########----------------##########
##########------------------##########
##########-------------------###########
##########--------------------##########
##########---------------------#########
##########----------------------######## T
##########--------- ----------########
##########--------- P ----------##########
#########--------- ----------#########
#########----------------------#########
########----------------------########
########--------------------########
#######--------------------#######
######------------------######
######----------------######
####--------------####
##----------##
Harvard Convention
Moment Tensor:
R T F
-5.43e+23 1.01e+23 -1.79e+22
1.01e+23 -1.88e+22 -3.82e+21
-1.79e+22 -3.82e+21 5.62e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA//index.html
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Normal fault CMT 042101E EASTERN IDAHO Date: 2001/ 4/21 Centroid Time: 17:19: 2.4 GMT Lat= 43.02 Lon=-111.29 Depth= 15.0 Half duration= 1.1 Centroid time minus hypocenter time: 5.4 Moment Tensor: Expo=24 -1.050 0.030 1.020 -0.170 0.110 0.040 Mw = 5.3 mb = 5.4 Ms = 4.9 Scalar Moment = 1.05e+24 Fault plane: strike=11 dip=43 slip=-77 Fault plane: strike=173 dip=48 slip=-102 |
STK = 190
DIP = 45
RAKE = -75
MW = 5.10
HS = 10
The waveform inversion is preferred. The surface-eave solution is equivalent.
The following compares this source inversion to others
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 0.01 n 3 lp c 0.05 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 90 -15 4.59 0.1806
WVFGRD96 1.0 220 90 -10 4.62 0.1929
WVFGRD96 2.0 220 90 -10 4.70 0.2182
WVFGRD96 3.0 220 75 -25 4.79 0.2330
WVFGRD96 4.0 220 80 -50 4.89 0.2619
WVFGRD96 5.0 215 70 -50 4.92 0.3107
WVFGRD96 6.0 205 55 -55 4.96 0.3766
WVFGRD96 7.0 200 50 -65 5.01 0.4382
WVFGRD96 8.0 200 50 -65 5.08 0.4935
WVFGRD96 9.0 200 50 -65 5.10 0.5410
WVFGRD96 10.0 190 45 -75 5.10 0.5578
WVFGRD96 11.0 200 50 -65 5.09 0.5493
WVFGRD96 12.0 200 50 -65 5.08 0.5291
WVFGRD96 13.0 200 50 -60 5.06 0.5032
WVFGRD96 14.0 35 55 -35 5.05 0.4806
WVFGRD96 15.0 45 70 -15 5.08 0.4642
WVFGRD96 16.0 45 70 -15 5.08 0.4499
WVFGRD96 17.0 45 75 -10 5.09 0.4354
WVFGRD96 18.0 45 75 -10 5.08 0.4200
WVFGRD96 19.0 45 80 -5 5.09 0.4023
WVFGRD96 20.0 45 80 -5 5.09 0.3861
WVFGRD96 21.0 45 80 -5 5.09 0.3702
WVFGRD96 22.0 225 90 5 5.10 0.3580
WVFGRD96 23.0 225 90 10 5.10 0.3510
WVFGRD96 24.0 225 90 10 5.10 0.3437
WVFGRD96 25.0 225 90 10 5.10 0.3366
WVFGRD96 26.0 225 90 10 5.10 0.3269
WVFGRD96 27.0 225 90 10 5.10 0.3192
WVFGRD96 28.0 225 85 10 5.10 0.3094
WVFGRD96 29.0 225 85 10 5.11 0.3014
The best solution is
WVFGRD96 10.0 190 45 -75 5.10 0.5578
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 0.01 n 3 lp c 0.05 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= 194.25
DIP= 51.62
RAKE= -77.75
OR
STK= 354.97
DIP= 40.00
RAKE= -105.00
DEPTH = 10.0 km
Mw = 5.22
Best Fit 0.9010 - 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 HWUT 186 147 iP_D BW06 95 151 eP_C HLID 287 256 iP_C BOZ 356 304 iP_D DUG 202 325 iP_D ELK 234 401 iP_D MVU 188 495 iP_D
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) HWUT 186 147 BW06 95 151 HLID 287 256 BOZ 356 304 DUG 202 325 ELK 234 401 MVU 188 495 BMN 242 559 ISCO 124 595 WVOR 267 596 RSSD 75 609 TPH 224 730 NEW 325 743 PAHR 245 758 PIN 281 774 WCN 243 808 MLAC 230 863 TIN 224 874 DAC 218 909 CWC 221 920 MPM 216 924 LON 301 926 CMB 238 935 WDC 258 962 DBO 275 966 GSC 211 966 COR 285 976 ANMO 153 982 DAN 202 982 ISA 220 1010 GNW 304 1034 SQM 306 1075 CBKS 111 1082 SVD 209 1097 SAO 235 1098 OSI 217 1120 KNW 206 1122 PFO 205 1124 MWC 213 1126 SND 205 1135 WMC 206 1135 GLA 196 1136 RDM 207 1136 CRY 206 1138 PAS 213 1138 DGR 207 1140 FRD 205 1141 BZN 206 1143 PHL 226 1148 LVA2 205 1154 DJJ 214 1155 USC 214 1156 PLM 206 1164 TOV 216 1168 LLLB 321 1169 TUC 177 1179 JCS 204 1183 SBC 220 1186 RPV 213 1188 MONP 203 1197 CIA 212 1222 BAR 204 1227 SOL 207 1231 SNCC 216 1288 FFC 24 1481 CCM 101 1786 SLM 98 1842 UALR 112 1878 SIUC 100 1965 MPH 108 2042 BLO 93 2124 YKW3 356 2196 SSPA 84 2778
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 0.01 n 3 lp c 0.05 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 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=Tue Nov 13 14:15:13 CST 2007