The ANSS event ID is ak01834kwkl7 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak01834kwkl7/executive.
2018/03/09 07:32:37 59.751 -153.126 100.2 4.9 Alaska
USGS/SLU Moment Tensor Solution ENS 2018/03/09 07:32:37:0 59.75 -153.13 100.2 4.9 Alaska Stations used: AK.BRLK AK.CAPN AK.CNP AK.FIRE AK.GHO AK.HOM AK.RC01 AK.SCM AK.SKN AK.SSN AK.SWD AT.PMR AT.SVW2 AV.ILSW II.KDAK TA.L19K TA.M19K TA.M20K TA.M22K TA.N17K TA.N18K TA.N19K TA.O16K TA.O18K TA.O19K TA.P18K TA.P19K TA.Q19K TA.Q20K Filtering commands used: cut o DIST/3.4 -20 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 3.13e+23 dyne-cm Mw = 4.93 Z = 112 km Plane Strike Dip Rake NP1 299 64 146 NP2 45 60 30 Principal Axes: Axis Value Plunge Azimuth T 3.13e+23 41 260 N 0.00e+00 49 86 P -3.13e+23 3 353 Moment Tensor: (dyne-cm) Component Value Mxx -3.02e+23 Mxy 6.77e+22 Mxz -4.05e+22 Myy 1.67e+23 Myz -1.51e+23 Mzz 1.35e+23 --- P -------- ------- ------------ ---------------------------- ------------------------------ --------------------------------## #########-----------------------#### #################----------------##### ######################-----------####### #########################--------####### #############################----######### ########################################## ######## ###################---######### ######## T ##################------####### ####### ################---------##### ########################-------------### #####################----------------# ##################------------------ #############--------------------- #######----------------------- ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 1.35e+23 -4.05e+22 1.51e+23 -4.05e+22 -3.02e+23 -6.77e+22 1.51e+23 -6.77e+22 1.67e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180309073237/index.html |
STK = 45 DIP = 60 RAKE = 30 MW = 4.93 HS = 112.0
The NDK file is 20180309073237.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 2018/03/09 07:32:37:0 59.75 -153.13 100.2 4.9 Alaska Stations used: AK.BRLK AK.CAPN AK.CNP AK.FIRE AK.GHO AK.HOM AK.RC01 AK.SCM AK.SKN AK.SSN AK.SWD AT.PMR AT.SVW2 AV.ILSW II.KDAK TA.L19K TA.M19K TA.M20K TA.M22K TA.N17K TA.N18K TA.N19K TA.O16K TA.O18K TA.O19K TA.P18K TA.P19K TA.Q19K TA.Q20K Filtering commands used: cut o DIST/3.4 -20 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 3.13e+23 dyne-cm Mw = 4.93 Z = 112 km Plane Strike Dip Rake NP1 299 64 146 NP2 45 60 30 Principal Axes: Axis Value Plunge Azimuth T 3.13e+23 41 260 N 0.00e+00 49 86 P -3.13e+23 3 353 Moment Tensor: (dyne-cm) Component Value Mxx -3.02e+23 Mxy 6.77e+22 Mxz -4.05e+22 Myy 1.67e+23 Myz -1.51e+23 Mzz 1.35e+23 --- P -------- ------- ------------ ---------------------------- ------------------------------ --------------------------------## #########-----------------------#### #################----------------##### ######################-----------####### #########################--------####### #############################----######### ########################################## ######## ###################---######### ######## T ##################------####### ####### ################---------##### ########################-------------### #####################----------------# ##################------------------ #############--------------------- #######----------------------- ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 1.35e+23 -4.05e+22 1.51e+23 -4.05e+22 -3.02e+23 -6.77e+22 1.51e+23 -6.77e+22 1.67e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180309073237/index.html |
Regional Moment Tensor (Mwr) Moment 3.212e+16 N-m Magnitude 4.9 Mwr Depth 102.0 km Percent DC 75 % Half Duration – Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 299 57 148 NP2 48 63 37 Principal Axes Axis Value Plunge Azimuth T 3.402e+16 N-m 44 266 N -0.421e+16 N-m 45 79 P -2.981e+16 N-m 4 172 |
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/3.4 -20 o DIST/3.4 +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 2.0 70 45 -80 3.93 0.1302 WVFGRD96 4.0 285 60 -25 3.95 0.1473 WVFGRD96 6.0 280 65 -25 4.01 0.1671 WVFGRD96 8.0 280 65 -25 4.10 0.1829 WVFGRD96 10.0 280 65 -25 4.15 0.1906 WVFGRD96 12.0 285 70 -25 4.19 0.1973 WVFGRD96 14.0 285 70 -25 4.22 0.1980 WVFGRD96 16.0 285 70 -30 4.25 0.1946 WVFGRD96 18.0 30 60 25 4.27 0.1888 WVFGRD96 20.0 30 65 25 4.30 0.1945 WVFGRD96 22.0 30 65 20 4.33 0.1989 WVFGRD96 24.0 215 75 25 4.35 0.2056 WVFGRD96 26.0 215 75 25 4.37 0.2130 WVFGRD96 28.0 215 75 20 4.39 0.2217 WVFGRD96 30.0 215 75 20 4.41 0.2303 WVFGRD96 32.0 215 75 20 4.43 0.2354 WVFGRD96 34.0 215 75 20 4.44 0.2379 WVFGRD96 36.0 215 70 15 4.46 0.2369 WVFGRD96 38.0 35 80 5 4.50 0.2438 WVFGRD96 40.0 35 75 10 4.56 0.2579 WVFGRD96 42.0 30 65 5 4.59 0.2682 WVFGRD96 44.0 30 65 0 4.62 0.2798 WVFGRD96 46.0 30 65 10 4.64 0.2971 WVFGRD96 48.0 35 60 10 4.68 0.3158 WVFGRD96 50.0 35 60 10 4.70 0.3324 WVFGRD96 52.0 35 60 10 4.71 0.3468 WVFGRD96 54.0 35 55 5 4.74 0.3607 WVFGRD96 56.0 35 55 5 4.75 0.3712 WVFGRD96 58.0 35 55 5 4.77 0.3843 WVFGRD96 60.0 35 55 5 4.78 0.3975 WVFGRD96 62.0 40 55 10 4.80 0.4108 WVFGRD96 64.0 40 55 10 4.81 0.4257 WVFGRD96 66.0 40 55 10 4.82 0.4383 WVFGRD96 68.0 40 55 10 4.83 0.4511 WVFGRD96 70.0 40 55 15 4.83 0.4632 WVFGRD96 72.0 45 55 25 4.84 0.4773 WVFGRD96 74.0 45 55 25 4.85 0.4919 WVFGRD96 76.0 45 55 25 4.86 0.5055 WVFGRD96 78.0 45 55 25 4.86 0.5179 WVFGRD96 80.0 45 55 25 4.87 0.5311 WVFGRD96 82.0 45 60 25 4.88 0.5431 WVFGRD96 84.0 45 60 25 4.88 0.5539 WVFGRD96 86.0 45 60 25 4.89 0.5651 WVFGRD96 88.0 45 60 25 4.89 0.5734 WVFGRD96 90.0 45 60 25 4.90 0.5817 WVFGRD96 92.0 45 60 25 4.90 0.5893 WVFGRD96 94.0 45 60 30 4.90 0.5952 WVFGRD96 96.0 45 60 30 4.90 0.6019 WVFGRD96 98.0 45 60 30 4.91 0.6081 WVFGRD96 100.0 45 60 30 4.91 0.6125 WVFGRD96 102.0 45 60 30 4.91 0.6149 WVFGRD96 104.0 45 60 30 4.92 0.6180 WVFGRD96 106.0 45 60 30 4.92 0.6203 WVFGRD96 108.0 45 60 30 4.92 0.6216 WVFGRD96 110.0 45 60 30 4.92 0.6223 WVFGRD96 112.0 45 60 30 4.93 0.6224 WVFGRD96 114.0 45 60 30 4.93 0.6212 WVFGRD96 116.0 45 60 30 4.93 0.6190 WVFGRD96 118.0 45 60 30 4.93 0.6173 WVFGRD96 120.0 45 60 30 4.93 0.6154 WVFGRD96 122.0 45 60 30 4.93 0.6131 WVFGRD96 124.0 45 60 30 4.94 0.6102 WVFGRD96 126.0 45 60 30 4.94 0.6073 WVFGRD96 128.0 45 60 30 4.94 0.6051 WVFGRD96 130.0 45 60 30 4.94 0.6017 WVFGRD96 132.0 45 60 30 4.94 0.5989 WVFGRD96 134.0 40 65 25 4.94 0.5963 WVFGRD96 136.0 40 65 25 4.95 0.5935 WVFGRD96 138.0 40 65 25 4.95 0.5926 WVFGRD96 140.0 40 65 25 4.95 0.5906 WVFGRD96 142.0 40 65 25 4.95 0.5887 WVFGRD96 144.0 40 65 25 4.95 0.5865 WVFGRD96 146.0 40 65 25 4.95 0.5845 WVFGRD96 148.0 40 65 25 4.96 0.5807
The best solution is
WVFGRD96 112.0 45 60 30 4.93 0.6224
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/3.4 -20 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 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