The ANSS event ID is ak010buy7ula and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak010buy7ula/executive.
2010/09/15 16:06:41 59.861 -153.176 121.0 5 Alaska
USGS/SLU Moment Tensor Solution ENS 2010/09/15 16:06:41:0 59.86 -153.18 121.0 5.0 Alaska Stations used: AK.BRLK AK.CNP AK.FID AK.GLI AK.RC01 AK.SAW AK.SCM AK.SII AK.SSN AK.SWD AT.OHAK AT.PMR AT.SVW2 AT.TTA 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 = 1.23e+23 dyne-cm Mw = 4.66 Z = 114 km Plane Strike Dip Rake NP1 70 75 45 NP2 325 47 159 Principal Axes: Axis Value Plunge Azimuth T 1.23e+23 42 298 N 0.00e+00 43 85 P -1.23e+23 17 192 Moment Tensor: (dyne-cm) Component Value Mxx -9.24e+22 Mxy -5.04e+22 Mxz 6.31e+22 Myy 4.89e+22 Myz -4.69e+22 Mzz 4.35e+22 -------------- ---------------------- ###########----------------- ################-------------- ####################-------------- ########################------------ ####### ################------------ ######## T ##################----------# ######## ###################-------### ################################---####### ################################-######### #############################----######### ########################----------######## ##################---------------####### ###########-----------------------###### ---------------------------------##### --------------------------------#### ------------------------------#### ----------------------------## --------- --------------## ------ P ------------- -- --------- Global CMT Convention Moment Tensor: R T P 4.35e+22 6.31e+22 4.69e+22 6.31e+22 -9.24e+22 5.04e+22 4.69e+22 5.04e+22 4.89e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100915160641/index.html |
STK = 70 DIP = 75 RAKE = 45 MW = 4.66 HS = 114.0
The NDK file is 20100915160641.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 2010/09/15 16:06:41:0 59.86 -153.18 121.0 5.0 Alaska Stations used: AK.BRLK AK.CNP AK.FID AK.GLI AK.RC01 AK.SAW AK.SCM AK.SII AK.SSN AK.SWD AT.OHAK AT.PMR AT.SVW2 AT.TTA 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 = 1.23e+23 dyne-cm Mw = 4.66 Z = 114 km Plane Strike Dip Rake NP1 70 75 45 NP2 325 47 159 Principal Axes: Axis Value Plunge Azimuth T 1.23e+23 42 298 N 0.00e+00 43 85 P -1.23e+23 17 192 Moment Tensor: (dyne-cm) Component Value Mxx -9.24e+22 Mxy -5.04e+22 Mxz 6.31e+22 Myy 4.89e+22 Myz -4.69e+22 Mzz 4.35e+22 -------------- ---------------------- ###########----------------- ################-------------- ####################-------------- ########################------------ ####### ################------------ ######## T ##################----------# ######## ###################-------### ################################---####### ################################-######### #############################----######### ########################----------######## ##################---------------####### ###########-----------------------###### ---------------------------------##### --------------------------------#### ------------------------------#### ----------------------------## --------- --------------## ------ P ------------- -- --------- Global CMT Convention Moment Tensor: R T P 4.35e+22 6.31e+22 4.69e+22 6.31e+22 -9.24e+22 5.04e+22 4.69e+22 5.04e+22 4.89e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100915160641/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.
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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 2.0 340 80 -20 3.75 0.2091 WVFGRD96 4.0 165 85 10 3.83 0.2575 WVFGRD96 6.0 160 90 10 3.90 0.2731 WVFGRD96 8.0 340 85 -10 3.96 0.2936 WVFGRD96 10.0 340 70 -5 4.00 0.2977 WVFGRD96 12.0 340 80 -10 4.03 0.3011 WVFGRD96 14.0 340 75 -15 4.04 0.3031 WVFGRD96 16.0 340 75 -15 4.06 0.3046 WVFGRD96 18.0 340 80 -15 4.08 0.3029 WVFGRD96 20.0 340 80 -15 4.10 0.2980 WVFGRD96 22.0 80 75 20 4.12 0.3018 WVFGRD96 24.0 80 75 20 4.14 0.3110 WVFGRD96 26.0 80 75 20 4.16 0.3188 WVFGRD96 28.0 80 75 20 4.18 0.3246 WVFGRD96 30.0 80 75 20 4.19 0.3297 WVFGRD96 32.0 80 75 20 4.21 0.3328 WVFGRD96 34.0 80 75 15 4.23 0.3347 WVFGRD96 36.0 80 75 15 4.25 0.3364 WVFGRD96 38.0 75 80 15 4.30 0.3390 WVFGRD96 40.0 80 75 25 4.36 0.3424 WVFGRD96 42.0 80 75 25 4.38 0.3436 WVFGRD96 44.0 75 80 20 4.40 0.3451 WVFGRD96 46.0 75 80 20 4.42 0.3477 WVFGRD96 48.0 75 80 20 4.44 0.3497 WVFGRD96 50.0 75 80 20 4.45 0.3525 WVFGRD96 52.0 75 75 10 4.46 0.3618 WVFGRD96 54.0 75 75 10 4.48 0.3722 WVFGRD96 56.0 75 75 15 4.49 0.3819 WVFGRD96 58.0 75 75 15 4.50 0.3924 WVFGRD96 60.0 75 75 15 4.52 0.4024 WVFGRD96 62.0 75 75 15 4.53 0.4121 WVFGRD96 64.0 75 75 15 4.54 0.4244 WVFGRD96 66.0 75 75 20 4.55 0.4377 WVFGRD96 68.0 75 75 20 4.56 0.4482 WVFGRD96 70.0 70 80 25 4.59 0.4611 WVFGRD96 72.0 70 80 25 4.59 0.4721 WVFGRD96 74.0 70 80 25 4.60 0.4830 WVFGRD96 76.0 70 80 30 4.61 0.4930 WVFGRD96 78.0 70 80 30 4.61 0.5026 WVFGRD96 80.0 70 80 30 4.62 0.5115 WVFGRD96 82.0 70 80 35 4.62 0.5190 WVFGRD96 84.0 70 80 35 4.63 0.5265 WVFGRD96 86.0 70 80 35 4.63 0.5338 WVFGRD96 88.0 70 80 35 4.63 0.5396 WVFGRD96 90.0 70 80 35 4.63 0.5442 WVFGRD96 92.0 70 80 40 4.64 0.5482 WVFGRD96 94.0 70 75 35 4.65 0.5518 WVFGRD96 96.0 70 75 35 4.65 0.5559 WVFGRD96 98.0 70 75 40 4.65 0.5600 WVFGRD96 100.0 70 75 40 4.65 0.5632 WVFGRD96 102.0 70 75 40 4.65 0.5661 WVFGRD96 104.0 70 75 40 4.65 0.5675 WVFGRD96 106.0 70 75 40 4.65 0.5693 WVFGRD96 108.0 70 75 45 4.66 0.5703 WVFGRD96 110.0 70 75 45 4.66 0.5711 WVFGRD96 112.0 70 75 45 4.66 0.5716 WVFGRD96 114.0 70 75 45 4.66 0.5717 WVFGRD96 116.0 70 75 45 4.66 0.5713 WVFGRD96 118.0 70 75 45 4.66 0.5704 WVFGRD96 120.0 70 75 50 4.66 0.5698 WVFGRD96 122.0 70 75 50 4.66 0.5688 WVFGRD96 124.0 70 75 50 4.66 0.5678 WVFGRD96 126.0 70 75 50 4.66 0.5665 WVFGRD96 128.0 70 75 50 4.66 0.5654
The best solution is
WVFGRD96 114.0 70 75 45 4.66 0.5717
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