USGS/SLU Moment Tensor Solution ENS 2017/09/30 21:15:06:0 59.63 -152.23 81.3 4.1 Alaska Stations used: AK.BRLK AK.CNP AK.HOM AK.SSN AV.ILSW II.KDAK TA.N18K TA.N19K TA.O18K TA.O19K TA.O22K TA.P18K TA.P19K TA.Q19K TA.Q20K Filtering commands used: cut o DIST/3.4 -30 o DIST/3.4 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 2.69e+22 dyne-cm Mw = 4.22 Z = 82 km Plane Strike Dip Rake NP1 34 46 100 NP2 200 45 80 Principal Axes: Axis Value Plunge Azimuth T 2.69e+22 83 24 N 0.00e+00 7 207 P -2.69e+22 0 117 Moment Tensor: (dyne-cm) Component Value Mxx -5.23e+21 Mxy 1.11e+22 Mxz 3.11e+21 Myy -2.13e+22 Myz 1.13e+21 Mzz 2.65e+22 -------------# ------------########## ------------##############-- -----------#################-- -----------###################---- -----------#####################---- -----------######################----- -----------#######################------ ----------#######################------- ----------########## ###########-------- ----------########## T ###########-------- ---------########### ##########--------- ---------#######################---------- --------######################---------- --------#####################-------- -------####################--------- P ------##################----------- ------###############------------- ----############-------------- ----########---------------- ##-------------------- -------------- Global CMT Convention Moment Tensor: R T P 2.65e+22 3.11e+21 -1.13e+21 3.11e+21 -5.23e+21 -1.11e+22 -1.13e+21 -1.11e+22 -2.13e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170930211506/index.html |
STK = 200 DIP = 45 RAKE = 80 MW = 4.22 HS = 82.0
The NDK file is 20170930211506.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2017/09/30 21:15:06:0 59.63 -152.23 81.3 4.1 Alaska Stations used: AK.BRLK AK.CNP AK.HOM AK.SSN AV.ILSW II.KDAK TA.N18K TA.N19K TA.O18K TA.O19K TA.O22K TA.P18K TA.P19K TA.Q19K TA.Q20K Filtering commands used: cut o DIST/3.4 -30 o DIST/3.4 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 2.69e+22 dyne-cm Mw = 4.22 Z = 82 km Plane Strike Dip Rake NP1 34 46 100 NP2 200 45 80 Principal Axes: Axis Value Plunge Azimuth T 2.69e+22 83 24 N 0.00e+00 7 207 P -2.69e+22 0 117 Moment Tensor: (dyne-cm) Component Value Mxx -5.23e+21 Mxy 1.11e+22 Mxz 3.11e+21 Myy -2.13e+22 Myz 1.13e+21 Mzz 2.65e+22 -------------# ------------########## ------------##############-- -----------#################-- -----------###################---- -----------#####################---- -----------######################----- -----------#######################------ ----------#######################------- ----------########## ###########-------- ----------########## T ###########-------- ---------########### ##########--------- ---------#######################---------- --------######################---------- --------#####################-------- -------####################--------- P ------##################----------- ------###############------------- ----############-------------- ----########---------------- ##-------------------- -------------- Global CMT Convention Moment Tensor: R T P 2.65e+22 3.11e+21 -1.13e+21 3.11e+21 -5.23e+21 -1.11e+22 -1.13e+21 -1.11e+22 -2.13e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170930211506/index.html |
Moment 3.376e+15 N-m Magnitude 4.3 Mwr Depth 88.0 km Percent DC 94 % Half Duration – Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 210 39 88 NP2 32 51 91 Principal Axes Axis Value Plunge Azimuth T 3.429e+15 N-m 84 311 N -0.110e+15 N-m 1 211 P -3.319e+15 N-m 6 121 |
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for 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 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 -30 o DIST/3.4 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 20 50 -90 3.49 0.3142 WVFGRD96 4.0 65 30 -15 3.48 0.2448 WVFGRD96 6.0 75 30 0 3.50 0.2985 WVFGRD96 8.0 75 25 -5 3.59 0.3407 WVFGRD96 10.0 65 30 -25 3.63 0.3810 WVFGRD96 12.0 60 30 -40 3.66 0.4113 WVFGRD96 14.0 50 35 -50 3.71 0.4332 WVFGRD96 16.0 45 35 -60 3.74 0.4484 WVFGRD96 18.0 45 40 -55 3.77 0.4573 WVFGRD96 20.0 45 40 -55 3.80 0.4610 WVFGRD96 22.0 45 40 -50 3.82 0.4525 WVFGRD96 24.0 45 40 -50 3.84 0.4300 WVFGRD96 26.0 50 45 -40 3.86 0.3998 WVFGRD96 28.0 170 80 -65 3.84 0.3745 WVFGRD96 30.0 170 80 -65 3.86 0.3628 WVFGRD96 32.0 180 80 -65 3.87 0.3511 WVFGRD96 34.0 180 80 -65 3.88 0.3448 WVFGRD96 36.0 185 80 -65 3.89 0.3411 WVFGRD96 38.0 25 50 85 3.91 0.3413 WVFGRD96 40.0 25 50 90 4.03 0.4307 WVFGRD96 42.0 25 50 85 4.07 0.4551 WVFGRD96 44.0 25 50 85 4.09 0.4760 WVFGRD96 46.0 200 40 80 4.11 0.4994 WVFGRD96 48.0 200 40 80 4.13 0.5239 WVFGRD96 50.0 200 45 80 4.14 0.5484 WVFGRD96 52.0 200 45 80 4.16 0.5741 WVFGRD96 54.0 200 45 80 4.16 0.5991 WVFGRD96 56.0 200 45 80 4.17 0.6210 WVFGRD96 58.0 200 45 80 4.18 0.6432 WVFGRD96 60.0 200 45 80 4.18 0.6622 WVFGRD96 62.0 200 45 80 4.19 0.6781 WVFGRD96 64.0 200 45 80 4.19 0.6939 WVFGRD96 66.0 200 45 80 4.20 0.7047 WVFGRD96 68.0 200 45 80 4.20 0.7145 WVFGRD96 70.0 200 45 80 4.20 0.7234 WVFGRD96 72.0 200 45 80 4.21 0.7322 WVFGRD96 74.0 200 45 80 4.21 0.7378 WVFGRD96 76.0 205 40 85 4.22 0.7422 WVFGRD96 78.0 205 40 85 4.23 0.7444 WVFGRD96 80.0 35 50 95 4.23 0.7485 WVFGRD96 82.0 200 45 80 4.22 0.7486 WVFGRD96 84.0 30 50 95 4.23 0.7465 WVFGRD96 86.0 200 45 80 4.23 0.7470 WVFGRD96 88.0 30 50 95 4.24 0.7463 WVFGRD96 90.0 205 40 85 4.24 0.7408 WVFGRD96 92.0 30 45 95 4.24 0.7406 WVFGRD96 94.0 190 45 75 4.24 0.7361 WVFGRD96 96.0 30 45 95 4.25 0.7308 WVFGRD96 98.0 30 45 95 4.25 0.7277
The best solution is
WVFGRD96 82.0 200 45 80 4.22 0.7486
The mechanism correspond 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 and because the velocity model used in the predictions may not be perfect. 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 -30 o DIST/3.4 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: