USGS/SLU Moment Tensor Solution ENS 2020/01/09 05:42:18:0 17.94 -66.94 9.0 3.7 Puerto Rico Stations used: IU.SJG PR.AGPR PR.AOPR PR.CELP PR.CRPR PR.ECPR PR.EMPR PR.GCPR PR.HUMP PR.OBIP PR.PRSN PR.UUPR 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 = 5.13e+21 dyne-cm Mw = 3.74 Z = 11 km Plane Strike Dip Rake NP1 260 80 -15 NP2 353 75 -170 Principal Axes: Axis Value Plunge Azimuth T 5.13e+21 3 307 N 0.00e+00 72 47 P -5.13e+21 18 216 Moment Tensor: (dyne-cm) Component Value Mxx -1.23e+21 Mxy -4.66e+21 Mxz 1.38e+21 Myy 1.68e+21 Myz 6.31e+20 Mzz -4.54e+20 #####--------- ##########------------ ##############-------------- ################-------------- T ################---------------- #################---------------- #####################----------------- #######################----------------- #######################----------------- ######################--################## #############------------################# #######------------------################# ##-----------------------################# ------------------------################ ------------------------################ -----------------------############### ----------------------############## ----- -------------############# --- P -------------########### -- -------------########## ---------------####### ----------#### Global CMT Convention Moment Tensor: R T P -4.54e+20 1.38e+21 -6.31e+20 1.38e+21 -1.23e+21 4.66e+21 -6.31e+20 4.66e+21 1.68e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200109054218/index.html |
STK = 260 DIP = 80 RAKE = -15 MW = 3.74 HS = 11.0
The NDK file is 20200109054218.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/01/09 05:42:18:0 17.94 -66.94 9.0 3.7 Puerto Rico Stations used: IU.SJG PR.AGPR PR.AOPR PR.CELP PR.CRPR PR.ECPR PR.EMPR PR.GCPR PR.HUMP PR.OBIP PR.PRSN PR.UUPR 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 = 5.13e+21 dyne-cm Mw = 3.74 Z = 11 km Plane Strike Dip Rake NP1 260 80 -15 NP2 353 75 -170 Principal Axes: Axis Value Plunge Azimuth T 5.13e+21 3 307 N 0.00e+00 72 47 P -5.13e+21 18 216 Moment Tensor: (dyne-cm) Component Value Mxx -1.23e+21 Mxy -4.66e+21 Mxz 1.38e+21 Myy 1.68e+21 Myz 6.31e+20 Mzz -4.54e+20 #####--------- ##########------------ ##############-------------- ################-------------- T ################---------------- #################---------------- #####################----------------- #######################----------------- #######################----------------- ######################--################## #############------------################# #######------------------################# ##-----------------------################# ------------------------################ ------------------------################ -----------------------############### ----------------------############## ----- -------------############# --- P -------------########### -- -------------########## ---------------####### ----------#### Global CMT Convention Moment Tensor: R T P -4.54e+20 1.38e+21 -6.31e+20 1.38e+21 -1.23e+21 4.66e+21 -6.31e+20 4.66e+21 1.68e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200109054218/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 1.0 265 75 10 3.23 0.2936 WVFGRD96 2.0 265 70 10 3.40 0.4261 WVFGRD96 3.0 260 65 -10 3.46 0.4882 WVFGRD96 4.0 260 70 -15 3.51 0.5408 WVFGRD96 5.0 255 70 -15 3.53 0.5827 WVFGRD96 6.0 255 75 -15 3.57 0.6192 WVFGRD96 7.0 260 80 -15 3.62 0.6507 WVFGRD96 8.0 255 75 -20 3.66 0.6752 WVFGRD96 9.0 260 80 -15 3.69 0.6887 WVFGRD96 10.0 260 80 -15 3.72 0.6965 WVFGRD96 11.0 260 80 -15 3.74 0.6980 WVFGRD96 12.0 260 80 -10 3.75 0.6958 WVFGRD96 13.0 260 80 -10 3.76 0.6904 WVFGRD96 14.0 260 80 -10 3.78 0.6833 WVFGRD96 15.0 260 80 -5 3.79 0.6734 WVFGRD96 16.0 260 80 -5 3.80 0.6631 WVFGRD96 17.0 260 80 -5 3.81 0.6516 WVFGRD96 18.0 260 80 0 3.82 0.6401 WVFGRD96 19.0 260 80 0 3.83 0.6310 WVFGRD96 20.0 260 80 0 3.84 0.6223 WVFGRD96 21.0 260 75 0 3.84 0.6150 WVFGRD96 22.0 255 80 5 3.84 0.6076 WVFGRD96 23.0 255 80 10 3.85 0.6029 WVFGRD96 24.0 255 80 10 3.86 0.5966 WVFGRD96 25.0 245 70 0 3.85 0.5933 WVFGRD96 26.0 245 70 0 3.85 0.5884 WVFGRD96 27.0 245 70 0 3.86 0.5846 WVFGRD96 28.0 245 70 0 3.86 0.5797 WVFGRD96 29.0 245 70 -5 3.87 0.5740
The best solution is
WVFGRD96 11.0 260 80 -15 3.74 0.6980
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: