Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200125202036.US/index.html |
STK = 95 DIP = 30 RAKE = -70 MW = 4.74 HS = 17.0
The NDK file is 20200125202036.US.ndk The waveform inversion is preferred.
The following compares this source inversion to others
Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200125202036.US/index.html USGS/SLU Moment Tensor Solution ENS 2020/01/25 20:20:36:0 17.84 -66.82 11.5 5.0 Puerto Rico Stations used: GS.PR01 GS.PR02 GS.PR03 GS.PR04 GS.PR05 GS.PR06 IU.SJG PR.AGPR PR.CELP PR.CRPR PR.ECPR PR.GCPR PR.HUMP PR.MLPR PR.OBIP 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 = 1.62e+23 dyne-cm Mw = 4.74 Z = 17 km Plane Strike Dip Rake NP1 252 62 -101 NP2 95 30 -70 Principal Axes: Axis Value Plunge Azimuth T 1.62e+23 16 350 N 0.00e+00 10 258 P -1.62e+23 71 138 Moment Tensor: (dyne-cm) Component Value Mxx 1.36e+23 Mxy -1.59e+22 Mxz 8.01e+22 Myy -3.81e+21 Myz -4.12e+22 Mzz -1.32e+23 ### ######## ####### T ############ ########## ############### ############################## ################################## #################################### ########################---------##### #################----------------------- ############---------------------------- ##########-------------------------------- -######----------------------------------- -####----------------- ----------------- --##------------------ P ----------------# -#------------------- ---------------# ###-----------------------------------## ####-------------------------------### #####---------------------------#### #######----------------------##### ##########------------######## ############################ ###################### ############## Global CMT Convention Moment Tensor: R T P -1.32e+23 8.01e+22 4.12e+22 8.01e+22 1.36e+23 1.59e+22 4.12e+22 1.59e+22 -3.81e+21 USGS/SLU Moment Tensor Solution ENS 2020/01/25 20:20:38:0 18.01 -66.82 13.0 5.0 Puerto Rico Stations used: GS.PR01 GS.PR02 GS.PR03 GS.PR04 GS.PR05 GS.PR06 IU.SJG PR.AGPR PR.CELP PR.CRPR PR.ECPR PR.GCPR PR.HUMP PR.MLPR PR.OBIP 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 = 1.62e+23 dyne-cm Mw = 4.74 Z = 17 km Plane Strike Dip Rake NP1 252 62 -101 NP2 95 30 -70 Principal Axes: Axis Value Plunge Azimuth T 1.62e+23 16 350 N 0.00e+00 10 258 P -1.62e+23 71 138 Moment Tensor: (dyne-cm) Component Value Mxx 1.36e+23 Mxy -1.59e+22 Mxz 8.01e+22 Myy -3.81e+21 Myz -4.12e+22 Mzz -1.32e+23 ### ######## ####### T ############ ########## ############### ############################## ################################## #################################### ########################---------##### #################----------------------- ############---------------------------- ##########-------------------------------- -######----------------------------------- -####----------------- ----------------- --##------------------ P ----------------# -#------------------- ---------------# ###-----------------------------------## ####-------------------------------### #####---------------------------#### #######----------------------##### ##########------------######## ############################ ###################### ############## Global CMT Convention Moment Tensor: R T P -1.32e+23 8.01e+22 4.12e+22 8.01e+22 1.36e+23 1.59e+22 4.12e+22 1.59e+22 -3.81e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200125202038/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 85 45 -90 4.17 0.1665 WVFGRD96 2.0 75 45 -90 4.38 0.2583 WVFGRD96 3.0 265 50 -70 4.41 0.2263 WVFGRD96 4.0 280 70 -40 4.39 0.2277 WVFGRD96 5.0 120 20 -45 4.45 0.2703 WVFGRD96 6.0 110 20 -60 4.47 0.3137 WVFGRD96 7.0 105 20 -65 4.49 0.3474 WVFGRD96 8.0 100 20 -70 4.58 0.3800 WVFGRD96 9.0 100 25 -70 4.61 0.4086 WVFGRD96 10.0 100 25 -70 4.63 0.4330 WVFGRD96 11.0 95 25 -70 4.65 0.4525 WVFGRD96 12.0 95 25 -70 4.66 0.4692 WVFGRD96 13.0 95 25 -70 4.68 0.4823 WVFGRD96 14.0 95 30 -70 4.70 0.4944 WVFGRD96 15.0 95 30 -70 4.72 0.5030 WVFGRD96 16.0 95 30 -70 4.73 0.5079 WVFGRD96 17.0 95 30 -70 4.74 0.5091 WVFGRD96 18.0 95 30 -70 4.75 0.5064 WVFGRD96 19.0 100 35 -65 4.76 0.5030 WVFGRD96 20.0 100 35 -65 4.77 0.4989 WVFGRD96 21.0 100 35 -65 4.78 0.4964 WVFGRD96 22.0 100 35 -65 4.79 0.4904 WVFGRD96 23.0 100 35 -65 4.79 0.4825 WVFGRD96 24.0 100 35 -65 4.79 0.4757 WVFGRD96 25.0 100 40 -65 4.80 0.4689 WVFGRD96 26.0 100 40 -65 4.81 0.4632 WVFGRD96 27.0 100 40 -65 4.81 0.4580 WVFGRD96 28.0 100 40 -65 4.81 0.4529 WVFGRD96 29.0 95 40 -70 4.82 0.4489
The best solution is
WVFGRD96 17.0 95 30 -70 4.74 0.5091
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: