The ANSS event ID is us7000pfbs and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us7000pfbs/executive.
2025/02/21 21:26:33 49.631 -123.534 10.0 4.8 B.C., Canada
USGS/SLU Moment Tensor Solution ENS 2025/02/21 21:26:33:0 49.63 -123.53 10.0 4.8 B.C., Canada Stations used: C8.BCOV CN.BBB CN.CBB CN.CLRS CN.EDB CN.FHBB CN.GDR CN.GHNB CN.GOBB CN.HOLB CN.HOPB CN.LLLB CN.NLLB CN.OZB CN.PABB CN.PGC CN.PHC CN.PTRF CN.QEPB CN.SYMB CN.TOFB CN.TXDB CN.VDEB CN.VGZ CN.WOSB CN.WSLR PQ.ALBHB PQ.DAOB PQ.HAKB RE.GRCO2 UO.GROV UO.GRSDL UO.MINN UO.MONKS UO.NBFR UO.NECAN UO.SADL UO.SKAN UO.STONY UO.TRASK UO.TRIPT UO.VERN UO.WIKI US.NEW US.NLWA UW.ABER UW.BDGR UW.BHAM UW.BHCR UW.BLOB UW.BOIS UW.BUCKS UW.CBS UW.CCRK UW.CDF UW.CHIMA UW.CORE UW.COYL UW.CROWN UW.CVILL UW.DART UW.DAVN UW.DDRF UW.DEAL UW.DONK UW.DOORS UW.DOSE UW.DOTY UW.DY2 UW.EPH2 UW.EQUIL UW.ETW UW.FISH2 UW.FORK UW.GBB UW.GOBBL UW.GPW UW.H2O UW.HDW UW.HERD UW.HOPR UW.HOQUI UW.HTW UW.INGAL UW.KALA UW.KTSAP UW.LEID UW.LMONT UW.LOPEZ UW.LRIV UW.MBW2 UW.MDW UW.METAL UW.MONTE UW.MOODY UW.MULN UW.NIKE UW.OD2 UW.ODUC UW.OHOH UW.OLGA UW.OLQN UW.OMAK UW.OQNOB UW.OSQM UW.OSR UW.OT3 UW.OTR UW.PAN4H UW.PASS UW.RNWY UW.RPW2 UW.RVSD UW.SALO UW.SAW UW.SAXON UW.SHUK UW.SKAMO UW.SKOKO UW.SLDQ UW.SLF UW.SNAG UW.TNSKT UW.TOUT UW.TURTL UW.TWISP UW.WA2 UW.WAT2 UW.WINDI UW.WOLL UW.WYNO 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 0.07 n 3 Best Fitting Double Couple Mo = 1.27e+23 dyne-cm Mw = 4.67 Z = 15 km Plane Strike Dip Rake NP1 279 76 154 NP2 15 65 15 Principal Axes: Axis Value Plunge Azimuth T 1.27e+23 28 235 N 0.00e+00 61 73 P -1.27e+23 8 329 Moment Tensor: (dyne-cm) Component Value Mxx -5.74e+22 Mxy 1.03e+23 Mxz -4.47e+22 Myy 3.22e+22 Myz -3.39e+22 Mzz 2.52e+22 -------------# ---------------##### -- P ----------------####### --- ----------------######## -------------------------######### --------------------------########## ---------------------------########### ----------------------------############ ---------------------------############# #########################---############## ############################-----######### ###########################-----------#### ###########################--------------# #########################--------------- ###### ################--------------- ##### T ###############--------------- #### ##############--------------- ###################--------------- ################-------------- #############--------------- #########------------- ###----------- Global CMT Convention Moment Tensor: R T P 2.52e+22 -4.47e+22 3.39e+22 -4.47e+22 -5.74e+22 -1.03e+23 3.39e+22 -1.03e+23 3.22e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250221212633/index.html |
STK = 15 DIP = 65 RAKE = 15 MW = 4.67 HS = 15.0
The NDK file is 20250221212633.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 2025/02/21 21:26:33:0 49.63 -123.53 10.0 4.8 B.C., Canada Stations used: C8.BCOV CN.BBB CN.CBB CN.CLRS CN.EDB CN.FHBB CN.GDR CN.GHNB CN.GOBB CN.HOLB CN.HOPB CN.LLLB CN.NLLB CN.OZB CN.PABB CN.PGC CN.PHC CN.PTRF CN.QEPB CN.SYMB CN.TOFB CN.TXDB CN.VDEB CN.VGZ CN.WOSB CN.WSLR PQ.ALBHB PQ.DAOB PQ.HAKB RE.GRCO2 UO.GROV UO.GRSDL UO.MINN UO.MONKS UO.NBFR UO.NECAN UO.SADL UO.SKAN UO.STONY UO.TRASK UO.TRIPT UO.VERN UO.WIKI US.NEW US.NLWA UW.ABER UW.BDGR UW.BHAM UW.BHCR UW.BLOB UW.BOIS UW.BUCKS UW.CBS UW.CCRK UW.CDF UW.CHIMA UW.CORE UW.COYL UW.CROWN UW.CVILL UW.DART UW.DAVN UW.DDRF UW.DEAL UW.DONK UW.DOORS UW.DOSE UW.DOTY UW.DY2 UW.EPH2 UW.EQUIL UW.ETW UW.FISH2 UW.FORK UW.GBB UW.GOBBL UW.GPW UW.H2O UW.HDW UW.HERD UW.HOPR UW.HOQUI UW.HTW UW.INGAL UW.KALA UW.KTSAP UW.LEID UW.LMONT UW.LOPEZ UW.LRIV UW.MBW2 UW.MDW UW.METAL UW.MONTE UW.MOODY UW.MULN UW.NIKE UW.OD2 UW.ODUC UW.OHOH UW.OLGA UW.OLQN UW.OMAK UW.OQNOB UW.OSQM UW.OSR UW.OT3 UW.OTR UW.PAN4H UW.PASS UW.RNWY UW.RPW2 UW.RVSD UW.SALO UW.SAW UW.SAXON UW.SHUK UW.SKAMO UW.SKOKO UW.SLDQ UW.SLF UW.SNAG UW.TNSKT UW.TOUT UW.TURTL UW.TWISP UW.WA2 UW.WAT2 UW.WINDI UW.WOLL UW.WYNO 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 0.07 n 3 Best Fitting Double Couple Mo = 1.27e+23 dyne-cm Mw = 4.67 Z = 15 km Plane Strike Dip Rake NP1 279 76 154 NP2 15 65 15 Principal Axes: Axis Value Plunge Azimuth T 1.27e+23 28 235 N 0.00e+00 61 73 P -1.27e+23 8 329 Moment Tensor: (dyne-cm) Component Value Mxx -5.74e+22 Mxy 1.03e+23 Mxz -4.47e+22 Myy 3.22e+22 Myz -3.39e+22 Mzz 2.52e+22 -------------# ---------------##### -- P ----------------####### --- ----------------######## -------------------------######### --------------------------########## ---------------------------########### ----------------------------############ ---------------------------############# #########################---############## ############################-----######### ###########################-----------#### ###########################--------------# #########################--------------- ###### ################--------------- ##### T ###############--------------- #### ##############--------------- ###################--------------- ################-------------- #############--------------- #########------------- ###----------- Global CMT Convention Moment Tensor: R T P 2.52e+22 -4.47e+22 3.39e+22 -4.47e+22 -5.74e+22 -1.03e+23 3.39e+22 -1.03e+23 3.22e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250221212633/index.html |
W-phase Moment Tensor (Mww) Moment 2.050e+16 N-m Magnitude 4.81 Mww Depth 19.5 km Percent DC 88% Half Duration 0.50 s Catalog US Data Source US Contributor US Nodal Planes Plane Strike Dip Rake NP1 275 65 153 NP2 17 66 27 Principal Axes Axis Value Plunge Azimuth T 2.110e+16 36 237 N -0.126e+16 54 56 P -1.984e+16 0 146 |
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.
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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.
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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'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 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 195 85 5 4.21 0.2889 WVFGRD96 2.0 15 90 0 4.32 0.3725 WVFGRD96 3.0 10 70 -10 4.38 0.3997 WVFGRD96 4.0 10 65 -15 4.43 0.4255 WVFGRD96 5.0 10 55 -5 4.47 0.4579 WVFGRD96 6.0 10 55 -5 4.49 0.4946 WVFGRD96 7.0 10 60 -5 4.51 0.5295 WVFGRD96 8.0 15 55 15 4.57 0.5624 WVFGRD96 9.0 15 55 15 4.59 0.5957 WVFGRD96 10.0 15 60 20 4.61 0.6227 WVFGRD96 11.0 15 60 20 4.62 0.6456 WVFGRD96 12.0 15 60 20 4.64 0.6618 WVFGRD96 13.0 15 60 20 4.65 0.6719 WVFGRD96 14.0 15 65 20 4.66 0.6785 WVFGRD96 15.0 15 65 15 4.67 0.6815 WVFGRD96 16.0 15 65 15 4.68 0.6811 WVFGRD96 17.0 15 65 15 4.69 0.6778 WVFGRD96 18.0 15 65 15 4.70 0.6719 WVFGRD96 19.0 15 65 15 4.71 0.6640 WVFGRD96 20.0 15 65 15 4.71 0.6544 WVFGRD96 21.0 15 65 15 4.72 0.6433 WVFGRD96 22.0 15 65 15 4.73 0.6314 WVFGRD96 23.0 15 65 15 4.73 0.6185 WVFGRD96 24.0 15 65 15 4.74 0.6052 WVFGRD96 25.0 15 65 15 4.75 0.5915 WVFGRD96 26.0 15 65 15 4.75 0.5776 WVFGRD96 27.0 15 65 15 4.76 0.5635 WVFGRD96 28.0 15 65 15 4.76 0.5496 WVFGRD96 29.0 15 65 15 4.77 0.5357
The best solution is
WVFGRD96 15.0 15 65 15 4.67 0.6815
The mechanism corresponding 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, 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 0.07 n 3
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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. |
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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