The ANSS event ID is ak0158l9sor0 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0158l9sor0/executive.
2015/07/06 00:50:34 62.130 -150.789 70.7 4.8 Alaska
USGS/SLU Moment Tensor Solution ENS 2015/07/06 00:50:34:0 62.13 -150.79 70.7 4.8 Alaska Stations used: AK.BARN AK.BMR AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ AK.CTG AK.CUT AK.DOT AK.EYAK AK.FID AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT AK.ISLE AK.KLU AK.KNK AK.KTH AK.LOGN AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PAX AK.PPD AK.PPLA AK.PWL AK.RC01 AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.SWD AK.TGL AK.TRF AK.VRDI AK.WAX AK.WRH AT.MENT AT.MID AT.PMR II.KDAK IM.IL31 IU.COLA TA.I23K TA.K27K TA.L27K TA.M24K TA.N25K TA.POKR Filtering commands used: cut o DIST/3.3 -50 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.82e+23 dyne-cm Mw = 4.90 Z = 76 km Plane Strike Dip Rake NP1 337 84 130 NP2 75 40 10 Principal Axes: Axis Value Plunge Azimuth T 2.82e+23 38 282 N 0.00e+00 39 152 P -2.82e+23 28 37 Moment Tensor: (dyne-cm) Component Value Mxx -1.34e+23 Mxy -1.42e+23 Mxz -6.32e+22 Myy 8.60e+22 Myz -2.03e+23 Mzz 4.82e+22 -------------- ####------------------ ########-------------------- ##########------------- ---- #############------------ P ------ ###############----------- ------- #################--------------------- ###################--------------------- ###### ###########-------------------- ####### T ############-------------------# ####### ############------------------## #######################----------------### ########################--------------#### ########################-----------##### -#######################----------###### --######################------######## ----####################--########## -------#############---########### ----------------------######## ---------------------####### -------------------### -------------- Global CMT Convention Moment Tensor: R T P 4.82e+22 -6.32e+22 2.03e+23 -6.32e+22 -1.34e+23 1.42e+23 2.03e+23 1.42e+23 8.60e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150706005034/index.html |
STK = 75 DIP = 40 RAKE = 10 MW = 4.90 HS = 76.0
The NDK file is 20150706005034.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 2015/07/06 00:50:34:0 62.13 -150.79 70.7 4.8 Alaska Stations used: AK.BARN AK.BMR AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ AK.CTG AK.CUT AK.DOT AK.EYAK AK.FID AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT AK.ISLE AK.KLU AK.KNK AK.KTH AK.LOGN AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PAX AK.PPD AK.PPLA AK.PWL AK.RC01 AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.SWD AK.TGL AK.TRF AK.VRDI AK.WAX AK.WRH AT.MENT AT.MID AT.PMR II.KDAK IM.IL31 IU.COLA TA.I23K TA.K27K TA.L27K TA.M24K TA.N25K TA.POKR Filtering commands used: cut o DIST/3.3 -50 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.82e+23 dyne-cm Mw = 4.90 Z = 76 km Plane Strike Dip Rake NP1 337 84 130 NP2 75 40 10 Principal Axes: Axis Value Plunge Azimuth T 2.82e+23 38 282 N 0.00e+00 39 152 P -2.82e+23 28 37 Moment Tensor: (dyne-cm) Component Value Mxx -1.34e+23 Mxy -1.42e+23 Mxz -6.32e+22 Myy 8.60e+22 Myz -2.03e+23 Mzz 4.82e+22 -------------- ####------------------ ########-------------------- ##########------------- ---- #############------------ P ------ ###############----------- ------- #################--------------------- ###################--------------------- ###### ###########-------------------- ####### T ############-------------------# ####### ############------------------## #######################----------------### ########################--------------#### ########################-----------##### -#######################----------###### --######################------######## ----####################--########## -------#############---########### ----------------------######## ---------------------####### -------------------### -------------- Global CMT Convention Moment Tensor: R T P 4.82e+22 -6.32e+22 2.03e+23 -6.32e+22 -1.34e+23 1.42e+23 2.03e+23 1.42e+23 8.60e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150706005034/index.html |
Regional Moment Tensor (Mwr) Moment 2.579e+16 N-m Magnitude 4.87 Depth 65.0 km Percent DC 90% Half Duration – Catalog US (us10002nkt) Data Source US2 Contributor US2 Nodal Planes Plane Strike Dip Rake NP1 338 77 132 NP2 82 44 19 Principal Axes Axis Value Plunge Azimuth T 2.511 42 288 N 0.132 41 146 P -2.642 21 38 |
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 -50 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 65 45 -60 4.10 0.2045 WVFGRD96 4.0 70 75 -5 4.15 0.2333 WVFGRD96 6.0 70 70 0 4.22 0.2600 WVFGRD96 8.0 70 70 5 4.28 0.2873 WVFGRD96 10.0 70 70 5 4.32 0.3042 WVFGRD96 12.0 70 75 10 4.35 0.3141 WVFGRD96 14.0 70 75 15 4.37 0.3222 WVFGRD96 16.0 70 75 10 4.39 0.3306 WVFGRD96 18.0 70 70 10 4.40 0.3410 WVFGRD96 20.0 75 70 15 4.41 0.3550 WVFGRD96 22.0 75 70 15 4.43 0.3702 WVFGRD96 24.0 75 70 15 4.45 0.3846 WVFGRD96 26.0 75 70 15 4.47 0.3992 WVFGRD96 28.0 75 70 15 4.49 0.4141 WVFGRD96 30.0 75 70 15 4.51 0.4289 WVFGRD96 32.0 75 65 15 4.52 0.4450 WVFGRD96 34.0 75 65 15 4.55 0.4627 WVFGRD96 36.0 70 70 10 4.59 0.4823 WVFGRD96 38.0 70 70 10 4.62 0.5064 WVFGRD96 40.0 70 60 10 4.69 0.5187 WVFGRD96 42.0 70 60 10 4.71 0.5316 WVFGRD96 44.0 70 55 5 4.72 0.5475 WVFGRD96 46.0 70 55 5 4.74 0.5651 WVFGRD96 48.0 70 55 10 4.76 0.5828 WVFGRD96 50.0 75 50 10 4.77 0.6039 WVFGRD96 52.0 75 50 15 4.79 0.6230 WVFGRD96 54.0 75 50 15 4.80 0.6433 WVFGRD96 56.0 75 50 15 4.82 0.6609 WVFGRD96 58.0 75 50 15 4.83 0.6772 WVFGRD96 60.0 75 45 15 4.84 0.6940 WVFGRD96 62.0 75 45 15 4.85 0.7090 WVFGRD96 64.0 75 45 15 4.86 0.7215 WVFGRD96 66.0 75 45 15 4.87 0.7314 WVFGRD96 68.0 75 45 15 4.88 0.7392 WVFGRD96 70.0 75 45 15 4.89 0.7446 WVFGRD96 72.0 75 45 15 4.89 0.7480 WVFGRD96 74.0 75 40 10 4.90 0.7509 WVFGRD96 76.0 75 40 10 4.90 0.7520 WVFGRD96 78.0 75 40 10 4.91 0.7517 WVFGRD96 80.0 75 40 10 4.91 0.7496 WVFGRD96 82.0 75 40 10 4.92 0.7455 WVFGRD96 84.0 75 40 10 4.92 0.7404 WVFGRD96 86.0 75 40 10 4.92 0.7334 WVFGRD96 88.0 80 35 10 4.92 0.7263 WVFGRD96 90.0 80 35 10 4.92 0.7180 WVFGRD96 92.0 80 35 10 4.93 0.7108 WVFGRD96 94.0 80 35 10 4.93 0.7024 WVFGRD96 96.0 80 35 10 4.93 0.6925 WVFGRD96 98.0 80 35 10 4.93 0.6815
The best solution is
WVFGRD96 76.0 75 40 10 4.90 0.7520
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 -50 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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