USGS/SLU Moment Tensor Solution ENS 2020/01/24 02:46:59:0 19.94 -74.71 10.0 4.2 Cuba Stations used: CU.GTBY CW.CCCC CW.CHIV CW.MARV CW.NMDO CW.QMBU Filtering commands used: cut o DIST/3.3 -40 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 = 1.72e+22 dyne-cm Mw = 4.09 Z = 20 km Plane Strike Dip Rake NP1 188 66 -141 NP2 80 55 -30 Principal Axes: Axis Value Plunge Azimuth T 1.72e+22 7 312 N 0.00e+00 45 215 P -1.72e+22 44 48 Moment Tensor: (dyne-cm) Component Value Mxx 3.66e+21 Mxy -1.28e+22 Mxz -4.37e+21 Myy 4.41e+21 Myz -7.89e+21 Mzz -8.07e+21 #########----- ###########----------- #############--------------- ############----------------- T ###########-------------------- # ##########----------- -------- ###############----------- P --------- ###############------------ ---------- ###############------------------------- ###############--------------------------# ###############-------------------------## ###############-----------------------#### ###############---------------------###### -############--------------------####### ----#########----------------########### -------#####----------################ ------------######################## -----------####################### ---------##################### ---------################### ------################ ---########### Global CMT Convention Moment Tensor: R T P -8.07e+21 -4.37e+21 7.89e+21 -4.37e+21 3.66e+21 1.28e+22 7.89e+21 1.28e+22 4.41e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200124024659/index.html |
STK = 80 DIP = 55 RAKE = -30 MW = 4.09 HS = 20.0
The NDK file is 20200124024659.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/01/24 02:46:59:0 19.94 -74.71 10.0 4.2 Cuba Stations used: CU.GTBY CW.CCCC CW.CHIV CW.MARV CW.NMDO CW.QMBU Filtering commands used: cut o DIST/3.3 -40 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 = 1.72e+22 dyne-cm Mw = 4.09 Z = 20 km Plane Strike Dip Rake NP1 188 66 -141 NP2 80 55 -30 Principal Axes: Axis Value Plunge Azimuth T 1.72e+22 7 312 N 0.00e+00 45 215 P -1.72e+22 44 48 Moment Tensor: (dyne-cm) Component Value Mxx 3.66e+21 Mxy -1.28e+22 Mxz -4.37e+21 Myy 4.41e+21 Myz -7.89e+21 Mzz -8.07e+21 #########----- ###########----------- #############--------------- ############----------------- T ###########-------------------- # ##########----------- -------- ###############----------- P --------- ###############------------ ---------- ###############------------------------- ###############--------------------------# ###############-------------------------## ###############-----------------------#### ###############---------------------###### -############--------------------####### ----#########----------------########### -------#####----------################ ------------######################## -----------####################### ---------##################### ---------################### ------################ ---########### Global CMT Convention Moment Tensor: R T P -8.07e+21 -4.37e+21 7.89e+21 -4.37e+21 3.66e+21 1.28e+22 7.89e+21 1.28e+22 4.41e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200124024659/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.
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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:
cut o DIST/3.3 -40 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 1.0 125 90 0 3.53 0.2395 WVFGRD96 2.0 125 90 0 3.67 0.3157 WVFGRD96 3.0 125 85 0 3.76 0.3378 WVFGRD96 4.0 125 80 0 3.79 0.3088 WVFGRD96 5.0 125 65 -5 3.80 0.2932 WVFGRD96 6.0 175 75 -45 3.76 0.3227 WVFGRD96 7.0 170 70 -45 3.78 0.3557 WVFGRD96 8.0 170 70 -50 3.86 0.3702 WVFGRD96 9.0 285 45 30 3.88 0.4063 WVFGRD96 10.0 280 50 30 3.90 0.4356 WVFGRD96 11.0 280 50 30 3.92 0.4594 WVFGRD96 12.0 345 55 -45 3.98 0.4802 WVFGRD96 13.0 345 55 -45 4.01 0.4996 WVFGRD96 14.0 345 55 -50 4.04 0.5152 WVFGRD96 15.0 345 55 -45 4.05 0.5276 WVFGRD96 16.0 345 55 -45 4.06 0.5360 WVFGRD96 17.0 85 55 -25 4.05 0.5390 WVFGRD96 18.0 80 55 -30 4.06 0.5505 WVFGRD96 19.0 80 55 -30 4.07 0.5585 WVFGRD96 20.0 80 55 -30 4.09 0.5623 WVFGRD96 21.0 80 55 -30 4.10 0.5612 WVFGRD96 22.0 80 55 -30 4.11 0.5564 WVFGRD96 23.0 80 60 -30 4.12 0.5497 WVFGRD96 24.0 80 60 -30 4.13 0.5391 WVFGRD96 25.0 75 60 -35 4.13 0.5239 WVFGRD96 26.0 75 60 -35 4.13 0.5097 WVFGRD96 27.0 75 60 -35 4.14 0.4911 WVFGRD96 28.0 75 65 -40 4.13 0.4765 WVFGRD96 29.0 70 65 -45 4.14 0.4626
The best solution is
WVFGRD96 20.0 80 55 -30 4.09 0.5623
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 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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. |
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 Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.
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: