The ANSS event ID is pr2022218002 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/pr2022218002/executive.
2022/08/06 19:53:30 17.861 -66.900 12.0 4.2 Puerto Rico
USGS/SLU Moment Tensor Solution ENS 2022/08/06 19:53:30:0 17.86 -66.90 12.0 4.2 Puerto Rico Stations used: GS.PR01 GS.PR02 GS.PR03 GS.PR04 GS.PR05 IU.SJG PR.AGPR PR.AOPR PR.CELP PR.CRPR PR.ECPR PR.EMPR PR.GBPR PR.GCPR PR.HUMP PR.ICMP PR.IGPR PR.LSP PR.MLPR PR.MTP 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 = 2.43e+22 dyne-cm Mw = 4.19 Z = 13 km Plane Strike Dip Rake NP1 280 80 -20 NP2 14 70 -169 Principal Axes: Axis Value Plunge Azimuth T 2.43e+22 7 328 N 0.00e+00 68 74 P -2.43e+22 21 235 Moment Tensor: (dyne-cm) Component Value Mxx 1.04e+22 Mxy -2.06e+22 Mxz 6.99e+21 Myy -7.59e+21 Myz 5.25e+21 Mzz -2.84e+21 ############-- ################----- # T ################-------- ## ################--------- #######################----------- ########################------------ #########################------------- ##########################-------------- ##########################-------------- --------------------#######--------------- --------------------------###------------- --------------------------#########------- -------------------------###############-- ------------------------################ -----------------------################# ---- ---------------################ --- P --------------################ -- -------------################ ---------------############### -------------############### ---------############# ---########### Global CMT Convention Moment Tensor: R T P -2.84e+21 6.99e+21 -5.25e+21 6.99e+21 1.04e+22 2.06e+22 -5.25e+21 2.06e+22 -7.59e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220806195330/index.html |
STK = 280 DIP = 80 RAKE = -20 MW = 4.19 HS = 13.0
The NDK file is 20220806195330.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution ENS 2022/08/06 19:53:30:0 17.86 -66.90 12.0 4.2 Puerto Rico Stations used: GS.PR01 GS.PR02 GS.PR03 GS.PR04 GS.PR05 IU.SJG PR.AGPR PR.AOPR PR.CELP PR.CRPR PR.ECPR PR.EMPR PR.GBPR PR.GCPR PR.HUMP PR.ICMP PR.IGPR PR.LSP PR.MLPR PR.MTP 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 = 2.43e+22 dyne-cm Mw = 4.19 Z = 13 km Plane Strike Dip Rake NP1 280 80 -20 NP2 14 70 -169 Principal Axes: Axis Value Plunge Azimuth T 2.43e+22 7 328 N 0.00e+00 68 74 P -2.43e+22 21 235 Moment Tensor: (dyne-cm) Component Value Mxx 1.04e+22 Mxy -2.06e+22 Mxz 6.99e+21 Myy -7.59e+21 Myz 5.25e+21 Mzz -2.84e+21 ############-- ################----- # T ################-------- ## ################--------- #######################----------- ########################------------ #########################------------- ##########################-------------- ##########################-------------- --------------------#######--------------- --------------------------###------------- --------------------------#########------- -------------------------###############-- ------------------------################ -----------------------################# ---- ---------------################ --- P --------------################ -- -------------################ ---------------############### -------------############### ---------############# ---########### Global CMT Convention Moment Tensor: R T P -2.84e+21 6.99e+21 -5.25e+21 6.99e+21 1.04e+22 2.06e+22 -5.25e+21 2.06e+22 -7.59e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220806195330/index.html |
Regional Moment Tensor (Mwr) Moment 3.484e+15 N-m Magnitude 4.29 Mwr Depth 19.0 km Percent DC 65% Half Duration - Catalog US Data Source US 3 Contributor US 3 Nodal Planes Plane Strike Dip Rake NP1 10 71 -168 NP2 276 78 -19 Principal Axes Axis Value Plunge Azimuth T 3.763e+15 N-m 5 324 N -0.651e+15 N-m 68 65 P -3.112e+15 N-m 22 232 |
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
![]() |
The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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 are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 280 90 -5 3.63 0.2461 WVFGRD96 2.0 280 80 -5 3.79 0.3565 WVFGRD96 3.0 280 80 -15 3.88 0.4222 WVFGRD96 4.0 280 80 -25 3.94 0.4798 WVFGRD96 5.0 280 80 -30 3.98 0.5362 WVFGRD96 6.0 280 80 -25 4.01 0.5876 WVFGRD96 7.0 280 80 -25 4.04 0.6325 WVFGRD96 8.0 280 80 -30 4.10 0.6723 WVFGRD96 9.0 280 80 -25 4.12 0.7028 WVFGRD96 10.0 280 80 -25 4.14 0.7247 WVFGRD96 11.0 280 85 -20 4.16 0.7383 WVFGRD96 12.0 280 85 -20 4.18 0.7449 WVFGRD96 13.0 280 80 -20 4.19 0.7473 WVFGRD96 14.0 280 80 -20 4.20 0.7446 WVFGRD96 15.0 280 80 -20 4.21 0.7365 WVFGRD96 16.0 280 80 -20 4.22 0.7276 WVFGRD96 17.0 280 80 -20 4.23 0.7139 WVFGRD96 18.0 280 80 -20 4.24 0.7009 WVFGRD96 19.0 280 80 -20 4.25 0.6854 WVFGRD96 20.0 280 75 -20 4.25 0.6708 WVFGRD96 21.0 280 75 -20 4.26 0.6555 WVFGRD96 22.0 280 75 -20 4.27 0.6398 WVFGRD96 23.0 280 75 -20 4.27 0.6233 WVFGRD96 24.0 280 75 -20 4.28 0.6079 WVFGRD96 25.0 280 70 -20 4.28 0.5924 WVFGRD96 26.0 280 70 -20 4.28 0.5795 WVFGRD96 27.0 280 70 -20 4.29 0.5670 WVFGRD96 28.0 280 70 -20 4.29 0.5548 WVFGRD96 29.0 280 70 -20 4.30 0.5434
The best solution is
WVFGRD96 13.0 280 80 -20 4.19 0.7473
The mechanism corresponding 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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
![]() |
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
![]() |
Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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