USGS/SLU Moment Tensor Solution ENS 2017/04/18 11:59:33:0 61.51 -145.87 29.1 3.8 Alaska Stations used: AK.BARN AK.GHO AK.GLB AK.KNK AK.MCAR AK.PAX AK.PWL AK.SAW AK.SCM AK.VRDI AT.MENT AT.PMR TA.M24K TA.M26K TA.N25K Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 8.04e+21 dyne-cm Mw = 3.87 Z = 41 km Plane Strike Dip Rake NP1 321 58 -138 NP2 205 55 -40 Principal Axes: Axis Value Plunge Azimuth T 8.04e+21 2 82 N 0.00e+00 39 351 P -8.04e+21 51 175 Moment Tensor: (dyne-cm) Component Value Mxx -3.00e+21 Mxy 1.38e+21 Mxz 3.95e+21 Myy 7.85e+21 Myz -1.09e+20 Mzz -4.85e+21 -------------- ----------------###### ####------------############ ###########---################ ##############--################## ##############-----################# ##############--------################ #############------------############### ############---------------############ #############----------------########### T ############------------------########## ###########--------------------########### ###########---------------------########## #########-----------------------######## #########------------------------####### ########---------- -----------###### #######---------- P -----------##### ######---------- -----------#### ####------------------------## ####-----------------------# ##-------------------- -------------- Global CMT Convention Moment Tensor: R T P -4.85e+21 3.95e+21 1.09e+20 3.95e+21 -3.00e+21 -1.38e+21 1.09e+20 -1.38e+21 7.85e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170418115933/index.html |
STK = 205 DIP = 55 RAKE = -40 MW = 3.87 HS = 41.0
The NDK file is 20170418115933.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2017/04/18 11:59:33:0 61.51 -145.87 29.1 3.8 Alaska Stations used: AK.BARN AK.GHO AK.GLB AK.KNK AK.MCAR AK.PAX AK.PWL AK.SAW AK.SCM AK.VRDI AT.MENT AT.PMR TA.M24K TA.M26K TA.N25K Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 8.04e+21 dyne-cm Mw = 3.87 Z = 41 km Plane Strike Dip Rake NP1 321 58 -138 NP2 205 55 -40 Principal Axes: Axis Value Plunge Azimuth T 8.04e+21 2 82 N 0.00e+00 39 351 P -8.04e+21 51 175 Moment Tensor: (dyne-cm) Component Value Mxx -3.00e+21 Mxy 1.38e+21 Mxz 3.95e+21 Myy 7.85e+21 Myz -1.09e+20 Mzz -4.85e+21 -------------- ----------------###### ####------------############ ###########---################ ##############--################## ##############-----################# ##############--------################ #############------------############### ############---------------############ #############----------------########### T ############------------------########## ###########--------------------########### ###########---------------------########## #########-----------------------######## #########------------------------####### ########---------- -----------###### #######---------- P -----------##### ######---------- -----------#### ####------------------------## ####-----------------------# ##-------------------- -------------- Global CMT Convention Moment Tensor: R T P -4.85e+21 3.95e+21 1.09e+20 3.95e+21 -3.00e+21 -1.38e+21 1.09e+20 -1.38e+21 7.85e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170418115933/index.html |
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.
|
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:
cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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 1.0 135 60 25 3.00 0.1747 WVFGRD96 2.0 145 45 55 3.18 0.2358 WVFGRD96 3.0 155 45 70 3.29 0.2834 WVFGRD96 4.0 140 60 40 3.28 0.2711 WVFGRD96 5.0 295 55 -30 3.28 0.2905 WVFGRD96 6.0 295 60 -35 3.32 0.3122 WVFGRD96 7.0 295 60 -35 3.34 0.3283 WVFGRD96 8.0 290 55 -45 3.42 0.3364 WVFGRD96 9.0 295 60 -40 3.43 0.3434 WVFGRD96 10.0 295 60 -35 3.43 0.3467 WVFGRD96 11.0 295 60 -35 3.45 0.3468 WVFGRD96 12.0 295 65 -35 3.47 0.3451 WVFGRD96 13.0 295 65 -35 3.48 0.3429 WVFGRD96 14.0 295 65 -35 3.49 0.3388 WVFGRD96 15.0 295 65 -35 3.51 0.3333 WVFGRD96 16.0 300 70 -40 3.53 0.3264 WVFGRD96 17.0 300 70 -40 3.54 0.3186 WVFGRD96 18.0 215 75 50 3.52 0.3215 WVFGRD96 19.0 15 65 -40 3.54 0.3326 WVFGRD96 20.0 15 60 -35 3.56 0.3460 WVFGRD96 21.0 15 60 -35 3.58 0.3582 WVFGRD96 22.0 15 60 -35 3.60 0.3684 WVFGRD96 23.0 0 40 -55 3.60 0.3785 WVFGRD96 24.0 0 40 -55 3.62 0.3963 WVFGRD96 25.0 0 40 -55 3.63 0.4132 WVFGRD96 26.0 200 65 -40 3.64 0.4303 WVFGRD96 27.0 200 65 -40 3.65 0.4480 WVFGRD96 28.0 200 65 -45 3.66 0.4649 WVFGRD96 29.0 200 65 -45 3.68 0.4776 WVFGRD96 30.0 200 65 -45 3.69 0.4890 WVFGRD96 31.0 45 60 -15 3.75 0.5004 WVFGRD96 32.0 45 60 -15 3.76 0.5099 WVFGRD96 33.0 45 60 -15 3.77 0.5158 WVFGRD96 34.0 45 60 -15 3.78 0.5186 WVFGRD96 35.0 215 65 -25 3.77 0.5177 WVFGRD96 36.0 215 65 -25 3.77 0.5196 WVFGRD96 37.0 215 65 -25 3.78 0.5199 WVFGRD96 38.0 215 65 -25 3.79 0.5183 WVFGRD96 39.0 215 65 -25 3.81 0.5174 WVFGRD96 40.0 210 60 -35 3.86 0.5301 WVFGRD96 41.0 205 55 -40 3.87 0.5318 WVFGRD96 42.0 205 55 -40 3.88 0.5291 WVFGRD96 43.0 195 50 -50 3.89 0.5266 WVFGRD96 44.0 195 50 -50 3.90 0.5221 WVFGRD96 45.0 195 50 -50 3.91 0.5160 WVFGRD96 46.0 195 50 -50 3.91 0.5102 WVFGRD96 47.0 195 50 -50 3.91 0.5036 WVFGRD96 48.0 195 50 -50 3.92 0.4958 WVFGRD96 49.0 195 50 -50 3.92 0.4891
The best solution is
WVFGRD96 41.0 205 55 -40 3.87 0.5318
The mechanism correspond to the best fit is
|
The best fit as a function of depth is given in the following figure:
|
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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3
|
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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The WUS.model 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: