The ANSS event ID is ak01913ozsba and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak01913ozsba/executive.
2019/01/24 00:16:12 61.289 -150.081 43.7 3.8 Alaska
USGS/SLU Moment Tensor Solution ENS 2019/01/24 00:16:12:0 61.29 -150.08 43.7 3.8 Alaska Stations used: AK.FIRE AK.GHO AK.HIN AK.PWL AK.RC01 AK.SKN AK.SSN AT.PMR AV.SPU AV.STLK GM.AD09 TA.M22K Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.06e+22 dyne-cm Mw = 3.95 Z = 48 km Plane Strike Dip Rake NP1 194 78 -99 NP2 50 15 -55 Principal Axes: Axis Value Plunge Azimuth T 1.06e+22 32 291 N 0.00e+00 9 196 P -1.06e+22 56 93 Moment Tensor: (dyne-cm) Component Value Mxx 9.97e+20 Mxy -2.41e+21 Mxz 1.98e+21 Myy 3.34e+21 Myz -9.33e+21 Mzz -4.34e+21 ############-- ##############-------- ################------------ ################-------------- ##################---------------- ##################------------------ ##################-------------------# ##### ###########--------------------# ##### T ##########---------------------# ###### #########----------------------## ##################---------- ---------## ##################---------- P ---------## #################----------- --------### ################----------------------## ###############----------------------### ##############---------------------### #############--------------------### ############------------------#### ##########----------------#### -########--------------##### --####----------###### --############ Global CMT Convention Moment Tensor: R T P -4.34e+21 1.98e+21 9.33e+21 1.98e+21 9.97e+20 2.41e+21 9.33e+21 2.41e+21 3.34e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190124001612/index.html |
STK = 50 DIP = 15 RAKE = -55 MW = 3.95 HS = 48.0
The NDK file is 20190124001612.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 2019/01/24 00:16:12:0 61.29 -150.08 43.7 3.8 Alaska Stations used: AK.FIRE AK.GHO AK.HIN AK.PWL AK.RC01 AK.SKN AK.SSN AT.PMR AV.SPU AV.STLK GM.AD09 TA.M22K Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.06e+22 dyne-cm Mw = 3.95 Z = 48 km Plane Strike Dip Rake NP1 194 78 -99 NP2 50 15 -55 Principal Axes: Axis Value Plunge Azimuth T 1.06e+22 32 291 N 0.00e+00 9 196 P -1.06e+22 56 93 Moment Tensor: (dyne-cm) Component Value Mxx 9.97e+20 Mxy -2.41e+21 Mxz 1.98e+21 Myy 3.34e+21 Myz -9.33e+21 Mzz -4.34e+21 ############-- ##############-------- ################------------ ################-------------- ##################---------------- ##################------------------ ##################-------------------# ##### ###########--------------------# ##### T ##########---------------------# ###### #########----------------------## ##################---------- ---------## ##################---------- P ---------## #################----------- --------### ################----------------------## ###############----------------------### ##############---------------------### #############--------------------### ############------------------#### ##########----------------#### -########--------------##### --####----------###### --############ Global CMT Convention Moment Tensor: R T P -4.34e+21 1.98e+21 9.33e+21 1.98e+21 9.97e+20 2.41e+21 9.33e+21 2.41e+21 3.34e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190124001612/index.html |
Regional Moment Tensor (Mwr) Moment 1.016e+15 N-m Magnitude 3.94 Mwr Depth 51.0 km Percent DC 90% Half Duration - Catalog US Data Source US 2 Contributor US 2 Nodal Planes Plane Strike Dip Rake NP1 342 17 -122 NP2 194 76 -81 Principal Axes Axis Value Plunge Azimuth T 1.041e+15 N-m 30 277 N -0.052e+15 N-m 9 12 P -0.990e+15 N-m 58 116 |
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 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 170 90 5 3.31 0.2613 WVFGRD96 4.0 210 70 35 3.41 0.3048 WVFGRD96 6.0 15 60 -35 3.48 0.3294 WVFGRD96 8.0 15 60 -40 3.53 0.3469 WVFGRD96 10.0 15 65 -35 3.54 0.3484 WVFGRD96 12.0 90 55 25 3.58 0.3511 WVFGRD96 14.0 85 60 15 3.60 0.3589 WVFGRD96 16.0 85 55 15 3.61 0.3677 WVFGRD96 18.0 85 55 15 3.63 0.3776 WVFGRD96 20.0 85 55 15 3.64 0.3869 WVFGRD96 22.0 85 50 15 3.66 0.3954 WVFGRD96 24.0 85 50 15 3.68 0.4053 WVFGRD96 26.0 85 45 10 3.70 0.4149 WVFGRD96 28.0 85 45 10 3.72 0.4248 WVFGRD96 30.0 85 45 10 3.74 0.4361 WVFGRD96 32.0 85 45 10 3.75 0.4476 WVFGRD96 34.0 85 45 10 3.77 0.4573 WVFGRD96 36.0 75 20 -25 3.75 0.4637 WVFGRD96 38.0 60 15 -45 3.76 0.4856 WVFGRD96 40.0 55 10 -45 3.91 0.5017 WVFGRD96 42.0 55 15 -50 3.92 0.5046 WVFGRD96 44.0 50 15 -55 3.93 0.5082 WVFGRD96 46.0 50 15 -55 3.94 0.5090 WVFGRD96 48.0 50 15 -55 3.95 0.5100 WVFGRD96 50.0 50 15 -55 3.96 0.5090 WVFGRD96 52.0 55 15 -50 3.97 0.5077 WVFGRD96 54.0 65 15 -40 3.97 0.5066 WVFGRD96 56.0 70 15 -35 3.98 0.5070 WVFGRD96 58.0 70 15 -35 3.99 0.5070 WVFGRD96 60.0 75 15 -30 3.99 0.5075 WVFGRD96 62.0 75 15 -30 4.00 0.5072 WVFGRD96 64.0 80 15 -25 4.01 0.5078 WVFGRD96 66.0 80 15 -25 4.02 0.5065 WVFGRD96 68.0 85 15 -20 4.02 0.5068 WVFGRD96 70.0 85 15 -20 4.03 0.5048 WVFGRD96 72.0 85 15 -20 4.04 0.5045 WVFGRD96 74.0 90 15 -15 4.04 0.5027 WVFGRD96 76.0 90 15 -15 4.05 0.5004 WVFGRD96 78.0 90 15 -15 4.06 0.4984 WVFGRD96 80.0 90 15 -15 4.06 0.4950 WVFGRD96 82.0 95 20 -15 4.08 0.4924 WVFGRD96 84.0 95 20 -15 4.08 0.4882 WVFGRD96 86.0 100 20 -10 4.09 0.4838 WVFGRD96 88.0 100 20 -10 4.09 0.4785 WVFGRD96 90.0 95 20 -15 4.10 0.4727 WVFGRD96 92.0 95 20 -15 4.10 0.4667 WVFGRD96 94.0 90 20 -20 4.10 0.4605 WVFGRD96 96.0 90 20 -20 4.10 0.4536 WVFGRD96 98.0 90 20 -20 4.11 0.4472 WVFGRD96 100.0 90 20 -20 4.11 0.4399 WVFGRD96 102.0 95 20 -15 4.11 0.4324 WVFGRD96 104.0 95 20 -15 4.11 0.4253 WVFGRD96 106.0 120 20 15 4.12 0.4179 WVFGRD96 108.0 120 25 10 4.14 0.4116 WVFGRD96 110.0 120 25 10 4.14 0.4032 WVFGRD96 112.0 120 25 10 4.14 0.3891 WVFGRD96 114.0 120 25 10 4.13 0.3577 WVFGRD96 116.0 130 30 -15 4.17 0.3223 WVFGRD96 118.0 130 30 -20 4.17 0.2911 WVFGRD96 120.0 130 30 -20 4.15 0.2557 WVFGRD96 122.0 10 70 -80 4.08 0.2409 WVFGRD96 124.0 5 70 -75 4.09 0.2397 WVFGRD96 126.0 5 70 -75 4.09 0.2383 WVFGRD96 128.0 5 70 -75 4.09 0.2371 WVFGRD96 130.0 5 70 -75 4.09 0.2353 WVFGRD96 132.0 5 70 -75 4.10 0.2336 WVFGRD96 134.0 5 70 -75 4.10 0.2318 WVFGRD96 136.0 5 70 -75 4.10 0.2307 WVFGRD96 138.0 5 70 -75 4.10 0.2289 WVFGRD96 140.0 10 70 -75 4.11 0.2250 WVFGRD96 142.0 10 70 -75 4.11 0.2159 WVFGRD96 144.0 10 70 -75 4.10 0.2001 WVFGRD96 146.0 20 65 -90 4.10 0.1815 WVFGRD96 148.0 210 25 -85 4.08 0.1588
The best solution is
WVFGRD96 48.0 50 15 -55 3.95 0.5100
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 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2
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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