USGS/SLU Moment Tensor Solution ENS 2020/09/06 21:38:46:0 17.92 -66.91 9.0 3.5 Puerto Rico Stations used: GS.PR01 GS.PR02 GS.PR03 GS.PR04 GS.PR05 GS.PR06 PR.AGPR PR.AOPR PR.CELP PR.CRPR PR.ECPR PR.HUMP PR.MLPR PR.PDPR PR.PRSN 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 = 1.76e+21 dyne-cm Mw = 3.43 Z = 11 km Plane Strike Dip Rake NP1 7 80 -170 NP2 275 80 -10 Principal Axes: Axis Value Plunge Azimuth T 1.76e+21 0 141 N 0.00e+00 76 50 P -1.76e+21 14 231 Moment Tensor: (dyne-cm) Component Value Mxx 4.00e+20 Mxy -1.67e+21 Mxz 2.60e+20 Myy -2.95e+20 Myz 3.24e+20 Mzz -1.04e+20 ##########---- ##############-------- #################----------- ##################------------ ####################-------------- #####################--------------- ######################---------------- #######################----------------- #######################----------------- #######-----------######------------------ ------------------------#########--------- -----------------------################--- -----------------------################### ----------------------################## ----------------------################## --------------------################## --- -------------################# -- P ------------################# ------------############ -------------############# T ----------############ -----######### Global CMT Convention Moment Tensor: R T P -1.04e+20 2.60e+20 -3.24e+20 2.60e+20 4.00e+20 1.67e+21 -3.24e+20 1.67e+21 -2.95e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200906213846/index.html |
STK = 275 DIP = 80 RAKE = -10 MW = 3.43 HS = 11.0
The NDK file is 20200906213846.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/09/06 21:38:46:0 17.92 -66.91 9.0 3.5 Puerto Rico Stations used: GS.PR01 GS.PR02 GS.PR03 GS.PR04 GS.PR05 GS.PR06 PR.AGPR PR.AOPR PR.CELP PR.CRPR PR.ECPR PR.HUMP PR.MLPR PR.PDPR PR.PRSN 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 = 1.76e+21 dyne-cm Mw = 3.43 Z = 11 km Plane Strike Dip Rake NP1 7 80 -170 NP2 275 80 -10 Principal Axes: Axis Value Plunge Azimuth T 1.76e+21 0 141 N 0.00e+00 76 50 P -1.76e+21 14 231 Moment Tensor: (dyne-cm) Component Value Mxx 4.00e+20 Mxy -1.67e+21 Mxz 2.60e+20 Myy -2.95e+20 Myz 3.24e+20 Mzz -1.04e+20 ##########---- ##############-------- #################----------- ##################------------ ####################-------------- #####################--------------- ######################---------------- #######################----------------- #######################----------------- #######-----------######------------------ ------------------------#########--------- -----------------------################--- -----------------------################### ----------------------################## ----------------------################## --------------------################## --- -------------################# -- P ------------################# ------------############ -------------############# T ----------############ -----######### Global CMT Convention Moment Tensor: R T P -1.04e+20 2.60e+20 -3.24e+20 2.60e+20 4.00e+20 1.67e+21 -3.24e+20 1.67e+21 -2.95e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200906213846/index.html |
(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.
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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 1.0 275 70 5 2.94 0.3052 WVFGRD96 2.0 275 65 5 3.11 0.4520 WVFGRD96 3.0 275 70 0 3.18 0.5545 WVFGRD96 4.0 275 75 -5 3.23 0.6265 WVFGRD96 5.0 275 75 -15 3.27 0.6815 WVFGRD96 6.0 275 75 -15 3.30 0.7278 WVFGRD96 7.0 275 80 -15 3.34 0.7684 WVFGRD96 8.0 275 75 -15 3.38 0.8000 WVFGRD96 9.0 275 75 -15 3.40 0.8193 WVFGRD96 10.0 275 80 -10 3.42 0.8262 WVFGRD96 11.0 275 80 -10 3.43 0.8291 WVFGRD96 12.0 275 80 -10 3.45 0.8242 WVFGRD96 13.0 275 80 -10 3.46 0.8155 WVFGRD96 14.0 275 80 -10 3.47 0.8036 WVFGRD96 15.0 275 75 -10 3.47 0.7909 WVFGRD96 16.0 275 75 -5 3.48 0.7771 WVFGRD96 17.0 275 75 -5 3.50 0.7611 WVFGRD96 18.0 275 75 -5 3.51 0.7457 WVFGRD96 19.0 275 75 -5 3.52 0.7284 WVFGRD96 20.0 275 75 -5 3.53 0.7104 WVFGRD96 21.0 275 75 -5 3.55 0.6920 WVFGRD96 22.0 275 75 -5 3.56 0.6758 WVFGRD96 23.0 275 75 -5 3.57 0.6566 WVFGRD96 24.0 275 75 -5 3.58 0.6391 WVFGRD96 25.0 280 80 -10 3.60 0.6224 WVFGRD96 26.0 280 80 -10 3.61 0.6069 WVFGRD96 27.0 280 80 -10 3.62 0.5934 WVFGRD96 28.0 280 80 -10 3.63 0.5826 WVFGRD96 29.0 280 80 -10 3.64 0.5728
The best solution is
WVFGRD96 11.0 275 80 -10 3.43 0.8291
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: