USGS/SLU Moment Tensor Solution ENS 2018/05/11 01:40:06:0 67.41 -146.43 6.4 4.4 Alaska Stations used: AK.BPAW AK.CCB AK.COLD AK.FYU AK.HDA AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PPD AK.SCRK AK.WRH IU.COLA TA.D22K TA.D24K TA.D25K TA.D27M TA.E22K TA.E24K TA.E25K TA.E27K TA.F20K TA.F21K TA.F24K TA.F28M TA.G21K TA.G23K TA.G27K TA.G29M TA.G30M TA.H21K TA.H23K TA.H24K TA.H29M TA.I21K TA.I23K TA.I26K TA.I28M TA.I29M TA.J25K TA.J26L TA.POKR TA.TOLK 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 = 1.84e+22 dyne-cm Mw = 4.11 Z = 14 km Plane Strike Dip Rake NP1 294 85 165 NP2 25 75 5 Principal Axes: Axis Value Plunge Azimuth T 1.84e+22 14 248 N 0.00e+00 74 96 P -1.84e+22 7 340 Moment Tensor: (dyne-cm) Component Value Mxx -1.37e+22 Mxy 1.17e+22 Mxz -3.71e+21 Myy 1.29e+22 Myz -3.27e+21 Mzz 8.02e+20 ------------ --- P --------------## ------ --------------##### -----------------------####### -------------------------######### --------------------------########## --------------------------############ #######--------------------############# ############--------------############## ##################--------################ ######################----################ #########################-################ ########################------############ ## #################-----------####### ## T ################---------------#### # ###############------------------- #################------------------- ##############-------------------- ###########------------------- #########------------------- ####------------------ -------------- Global CMT Convention Moment Tensor: R T P 8.02e+20 -3.71e+21 3.27e+21 -3.71e+21 -1.37e+22 -1.17e+22 3.27e+21 -1.17e+22 1.29e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180511014006/index.html |
STK = 25 DIP = 75 RAKE = 5 MW = 4.11 HS = 14.0
The NDK file is 20180511014006.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2018/05/11 01:40:06:0 67.41 -146.43 6.4 4.4 Alaska Stations used: AK.BPAW AK.CCB AK.COLD AK.FYU AK.HDA AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PPD AK.SCRK AK.WRH IU.COLA TA.D22K TA.D24K TA.D25K TA.D27M TA.E22K TA.E24K TA.E25K TA.E27K TA.F20K TA.F21K TA.F24K TA.F28M TA.G21K TA.G23K TA.G27K TA.G29M TA.G30M TA.H21K TA.H23K TA.H24K TA.H29M TA.I21K TA.I23K TA.I26K TA.I28M TA.I29M TA.J25K TA.J26L TA.POKR TA.TOLK 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 = 1.84e+22 dyne-cm Mw = 4.11 Z = 14 km Plane Strike Dip Rake NP1 294 85 165 NP2 25 75 5 Principal Axes: Axis Value Plunge Azimuth T 1.84e+22 14 248 N 0.00e+00 74 96 P -1.84e+22 7 340 Moment Tensor: (dyne-cm) Component Value Mxx -1.37e+22 Mxy 1.17e+22 Mxz -3.71e+21 Myy 1.29e+22 Myz -3.27e+21 Mzz 8.02e+20 ------------ --- P --------------## ------ --------------##### -----------------------####### -------------------------######### --------------------------########## --------------------------############ #######--------------------############# ############--------------############## ##################--------################ ######################----################ #########################-################ ########################------############ ## #################-----------####### ## T ################---------------#### # ###############------------------- #################------------------- ##############-------------------- ###########------------------- #########------------------- ####------------------ -------------- Global CMT Convention Moment Tensor: R T P 8.02e+20 -3.71e+21 3.27e+21 -3.71e+21 -1.37e+22 -1.17e+22 3.27e+21 -1.17e+22 1.29e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180511014006/index.html |
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
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 1.0 200 75 -10 3.90 0.4594 WVFGRD96 2.0 20 70 -10 3.95 0.4869 WVFGRD96 3.0 20 70 -15 3.97 0.5015 WVFGRD96 4.0 20 70 -15 3.98 0.5141 WVFGRD96 5.0 20 70 -10 3.99 0.5266 WVFGRD96 6.0 20 70 -10 4.01 0.5375 WVFGRD96 7.0 20 70 -10 4.02 0.5486 WVFGRD96 8.0 20 75 -10 4.03 0.5631 WVFGRD96 9.0 20 75 -10 4.04 0.5769 WVFGRD96 10.0 25 70 5 4.07 0.5891 WVFGRD96 11.0 25 70 5 4.08 0.5994 WVFGRD96 12.0 25 70 5 4.09 0.6062 WVFGRD96 13.0 25 75 5 4.10 0.6106 WVFGRD96 14.0 25 75 5 4.11 0.6119 WVFGRD96 15.0 25 70 5 4.12 0.6109 WVFGRD96 16.0 25 70 5 4.13 0.6083 WVFGRD96 17.0 25 70 5 4.14 0.6045 WVFGRD96 18.0 25 70 5 4.14 0.5992 WVFGRD96 19.0 25 70 5 4.15 0.5927 WVFGRD96 20.0 25 70 5 4.16 0.5851 WVFGRD96 21.0 25 70 5 4.17 0.5772 WVFGRD96 22.0 25 70 5 4.18 0.5681 WVFGRD96 23.0 25 65 5 4.19 0.5589 WVFGRD96 24.0 25 65 5 4.19 0.5489 WVFGRD96 25.0 25 65 5 4.20 0.5378 WVFGRD96 26.0 25 65 5 4.20 0.5259 WVFGRD96 27.0 25 65 10 4.21 0.5150 WVFGRD96 28.0 25 65 10 4.21 0.5040 WVFGRD96 29.0 25 65 10 4.21 0.4926
The best solution is
WVFGRD96 14.0 25 75 5 4.11 0.6119
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 CUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 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: