The ANSS event ID is ak010ft03mlb and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak010ft03mlb/executive.
2010/12/10 05:42:34 59.363 -135.153 0.6 4.6 Alaska
USGS/SLU Moment Tensor Solution ENS 2010/12/10 05:42:34:0 59.36 -135.15 0.6 4.6 Alaska Stations used: AK.BAL AK.BMR AK.CRQ AK.CTG AK.DCPH AT.CRAG AT.SKAG CN.BVCY CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 US.WRAK Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.22e+22 dyne-cm Mw = 4.35 Z = 0 km Plane Strike Dip Rake NP1 359 55 87 NP2 185 35 95 Principal Axes: Axis Value Plunge Azimuth T 4.22e+22 80 255 N 0.00e+00 3 1 P -4.22e+22 10 91 Moment Tensor: (dyne-cm) Component Value Mxx 6.62e+19 Mxy 1.35e+21 Mxz -1.75e+21 Myy -3.95e+22 Myz -1.46e+22 Mzz 3.95e+22 -----###------ ------########-------- -------###########---------- ------##############---------- -------################----------- -------##################----------- -------####################----------- --------####################------------ -------#####################------------ --------######################------------ -------######### ###########-------- - -------######### T ###########-------- P - -------######### ###########-------- - -------######################----------- -------#####################------------ -------####################----------- ------###################----------- ------##################---------- -----################--------- ------#############--------- ----###########------- ---######----- Global CMT Convention Moment Tensor: R T P 3.95e+22 -1.75e+21 1.46e+22 -1.75e+21 6.62e+19 -1.35e+21 1.46e+22 -1.35e+21 -3.95e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101210054234/index.html |
STK = 185 DIP = 35 RAKE = 95 MW = 4.35 HS = 0.5
The NDK file is 20101210054234.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 2010/12/10 05:42:34:0 59.36 -135.15 0.6 4.6 Alaska Stations used: AK.BAL AK.BMR AK.CRQ AK.CTG AK.DCPH AT.CRAG AT.SKAG CN.BVCY CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 US.WRAK Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.22e+22 dyne-cm Mw = 4.35 Z = 0 km Plane Strike Dip Rake NP1 359 55 87 NP2 185 35 95 Principal Axes: Axis Value Plunge Azimuth T 4.22e+22 80 255 N 0.00e+00 3 1 P -4.22e+22 10 91 Moment Tensor: (dyne-cm) Component Value Mxx 6.62e+19 Mxy 1.35e+21 Mxz -1.75e+21 Myy -3.95e+22 Myz -1.46e+22 Mzz 3.95e+22 -----###------ ------########-------- -------###########---------- ------##############---------- -------################----------- -------##################----------- -------####################----------- --------####################------------ -------#####################------------ --------######################------------ -------######### ###########-------- - -------######### T ###########-------- P - -------######### ###########-------- - -------######################----------- -------#####################------------ -------####################----------- ------###################----------- ------##################---------- -----################--------- ------#############--------- ----###########------- ---######----- Global CMT Convention Moment Tensor: R T P 3.95e+22 -1.75e+21 1.46e+22 -1.75e+21 6.62e+19 -1.35e+21 1.46e+22 -1.35e+21 -3.95e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101210054234/index.html |
|
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:
hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 185 35 95 4.35 0.7078 WVFGRD96 1.0 5 50 90 4.38 0.7068 WVFGRD96 2.0 180 25 80 4.48 0.6235 WVFGRD96 3.0 0 70 85 4.46 0.5600 WVFGRD96 4.0 10 20 105 4.44 0.5452 WVFGRD96 5.0 15 20 110 4.42 0.5443 WVFGRD96 6.0 175 75 85 4.40 0.5531 WVFGRD96 7.0 175 80 80 4.39 0.5595 WVFGRD96 8.0 315 10 55 4.39 0.5653 WVFGRD96 9.0 305 10 45 4.39 0.5682 WVFGRD96 10.0 300 10 40 4.43 0.5676 WVFGRD96 11.0 175 85 80 4.43 0.5648 WVFGRD96 12.0 355 90 -80 4.43 0.5573 WVFGRD96 13.0 355 90 -80 4.44 0.5492 WVFGRD96 14.0 210 30 -70 4.46 0.5504 WVFGRD96 15.0 210 30 -70 4.47 0.5497 WVFGRD96 16.0 215 30 -65 4.47 0.5469 WVFGRD96 17.0 215 30 -65 4.48 0.5402 WVFGRD96 18.0 215 30 -65 4.49 0.5316 WVFGRD96 19.0 225 30 -55 4.49 0.5205 WVFGRD96 20.0 215 25 -65 4.52 0.5068 WVFGRD96 21.0 215 25 -65 4.53 0.4943 WVFGRD96 22.0 220 25 -60 4.53 0.4809 WVFGRD96 23.0 220 25 -60 4.54 0.4654 WVFGRD96 24.0 220 25 -60 4.54 0.4493 WVFGRD96 25.0 225 25 -55 4.55 0.4329 WVFGRD96 26.0 230 25 -50 4.55 0.4151 WVFGRD96 27.0 320 10 -110 4.60 0.4069 WVFGRD96 28.0 160 80 -85 4.60 0.4013 WVFGRD96 29.0 160 80 -85 4.61 0.3951
The best solution is
WVFGRD96 0.5 185 35 95 4.35 0.7078
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
hp c 0.02 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 CUS.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 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00