2005/01/10 10:18:47 37.103 54.574 31.0 5.3 Iran
USGS Felt map for this earthquake
SLU Moment Tensor Solution 2005/01/10 10:18:47 37.103 54.574 31.0 5.3 Iran Best Fitting Double Couple Mo = 6.46e+23 dyne-cm Mw = 5.14 Z = 23 km Plane Strike Dip Rake NP1 272 58 116 NP2 50 40 55 Principal Axes: Axis Value Plunge Azimuth T 6.46e+23 66 232 N 0.00e+00 22 78 P -6.46e+23 10 344 Moment Tensor: (dyne-cm) Component Value Mxx -5.40e+23 Mxy 2.15e+23 Mxz -2.53e+23 Myy 1.92e+22 Myz -1.58e+23 Mzz 5.21e+23 ----------- ---- P --------------- ------- ------------------ ------------------------------ ---------------------------------# -----------------------------------# ------------------------------------## --------#####################--------### ----##############################--#### --###################################-#### ####################################----## ####################################------ ############## ##################------- ############# T ################-------- ############# ###############--------- ############################---------- #########################----------- #####################------------- ################-------------- ---------------------------- ---------------------- -------------- Harvard Convention Moment Tensor: R T F 5.21e+23 -2.53e+23 1.58e+23 -2.53e+23 -5.40e+23 -2.15e+23 1.58e+23 -2.15e+23 1.92e+22 Details of the solution is found at http://www.eas.slu.edu/Earthquake_Center/MECH.EU/20050110184729/index.html |
STK = 50 DIP = 40 RAKE = 55 MW = 5.14 HS = 23
The waveforms fit is nice, but the azimuthal control is not adequate
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 0.5 305 40 -95 4.11 0.1655 WVFGRD96 1.0 130 45 -90 4.20 0.1933 WVFGRD96 2.0 130 45 -90 4.33 0.2517 WVFGRD96 3.0 310 45 -95 4.46 0.2817 WVFGRD96 4.0 -5 55 -25 4.42 0.1942 WVFGRD96 5.0 0 80 10 4.43 0.1831 WVFGRD96 6.0 0 75 15 4.44 0.1831 WVFGRD96 7.0 0 75 15 4.46 0.1885 WVFGRD96 8.0 210 30 10 4.41 0.2005 WVFGRD96 9.0 215 30 15 4.43 0.2287 WVFGRD96 10.0 215 30 20 4.46 0.2562 WVFGRD96 11.0 220 30 25 4.48 0.2839 WVFGRD96 12.0 225 25 30 4.50 0.3113 WVFGRD96 13.0 230 25 35 4.52 0.3380 WVFGRD96 14.0 230 25 35 4.55 0.3642 WVFGRD96 15.0 230 25 35 4.57 0.3892 WVFGRD96 16.0 240 20 45 4.59 0.4132 WVFGRD96 17.0 240 20 45 4.61 0.4360 WVFGRD96 18.0 240 20 45 4.63 0.4570 WVFGRD96 19.0 245 20 45 4.64 0.4762 WVFGRD96 20.0 250 20 45 4.65 0.4935 WVFGRD96 21.0 250 20 45 4.68 0.5082 WVFGRD96 22.0 115 75 100 4.69 0.5226 WVFGRD96 23.0 105 80 80 4.73 0.5350 WVFGRD96 24.0 100 80 80 4.76 0.5464 WVFGRD96 25.0 105 80 80 4.76 0.5558 WVFGRD96 26.0 105 80 80 4.78 0.5634 WVFGRD96 27.0 105 80 75 4.80 0.5685 WVFGRD96 28.0 105 80 75 4.81 0.5712 WVFGRD96 29.0 105 80 75 4.82 0.5715 WVFGRD96 30.0 105 80 75 4.83 0.5697 WVFGRD96 31.0 105 80 75 4.84 0.5656 WVFGRD96 32.0 105 80 75 4.85 0.5589 WVFGRD96 33.0 110 75 75 4.85 0.5498 WVFGRD96 34.0 110 75 75 4.86 0.5388
The best solution is
WVFGRD96 29.0 105 80 75 4.82 0.5715
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= 272.43 DIP= 58.23 RAKE= 115.70 OR STK= 50.00 DIP= 40.00 RAKE= 55.00 DEPTH = 23.0 km Mw = 5.14 Best Fit 0.7418 - P-T axis plot gives solutions with FIT greater than FIT90
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion DAMV 233 288 iP_C ASAO 235 502 iP_C NASN 198 514 iP_C GRMI 289 612 eP_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. |
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) DAMV 233 288 ASAO 235 502 NASN 198 514 GRMI 289 612 SNGE 252 686 SHGR 224 771 KRBR 165 829 MAKU 288 892 GNI 294 910 GHIR 189 1000 ZHSF 144 1025 BNDS 171 1101 KIV 310 1248 MALT 280 1421 AKTK 10 1495 AML 66 1729 NIL 98 1745 EKS2 64 1749 KSDI 261 1771 AAK 64 1806 USP 62 1823 CHM 63 1836 KBK 64 1843 KZA 67 1855 TKM2 64 1901 ANTO 286 1912 CSS 269 1920 ULHL 66 1939 EIL 251 1997 ZRNK 28 2079 BRVK 30 2144 BVAR 30 2145 VOS 31 2147 ARU 7 2158 CHKZ 29 2210 PDG 64 2220 OBN 331 2409 KURK 44 2429
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:
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:
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
DATE=Fri Aug 17 10:48:09 CDT 2007