2010/09/15 16:06:41 59.8890 -153.0970 100.0 5.00
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/09/15 16:06:41:0 59.89 -153.10 100.0 5.0 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: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.46e+23 dyne-cm Mw = 4.71 Z = 117 km Plane Strike Dip Rake NP1 70 75 50 NP2 323 42 157 Principal Axes: Axis Value Plunge Azimuth T 1.46e+23 45 300 N 0.00e+00 38 82 P -1.46e+23 20 189 Moment Tensor: (dyne-cm) Component Value Mxx -1.08e+23 Mxy -5.15e+22 Mxz 8.28e+22 Myy 5.18e+22 Myz -5.60e+22 Mzz 5.60e+22 -------------- ---------------------- ############---------------- #################------------- ######################------------ #########################----------- ######## #################---------- ######### T ##################---------# ######### ###################------### #################################--####### ################################--######## #############################------####### ########################-----------####### ##################----------------###### ###########------------------------##### ----------------------------------#### ---------------------------------### -------------------------------### ----------- ---------------# ---------- P --------------# ------- ------------ -------------- Global CMT Convention Moment Tensor: R T P 5.60e+22 8.28e+22 5.60e+22 8.28e+22 -1.08e+23 5.15e+22 5.60e+22 5.15e+22 5.18e+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 = 50 MW = 4.71 HS = 117.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/09/15 16:06:41:0 59.89 -153.10 100.0 5.0 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: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.46e+23 dyne-cm Mw = 4.71 Z = 117 km Plane Strike Dip Rake NP1 70 75 50 NP2 323 42 157 Principal Axes: Axis Value Plunge Azimuth T 1.46e+23 45 300 N 0.00e+00 38 82 P -1.46e+23 20 189 Moment Tensor: (dyne-cm) Component Value Mxx -1.08e+23 Mxy -5.15e+22 Mxz 8.28e+22 Myy 5.18e+22 Myz -5.60e+22 Mzz 5.60e+22 -------------- ---------------------- ############---------------- #################------------- ######################------------ #########################----------- ######## #################---------- ######### T ##################---------# ######### ###################------### #################################--####### ################################--######## #############################------####### ########################-----------####### ##################----------------###### ###########------------------------##### ----------------------------------#### ---------------------------------### -------------------------------### ----------- ---------------# ---------- P --------------# ------- ------------ -------------- Global CMT Convention Moment Tensor: R T P 5.60e+22 8.28e+22 5.60e+22 8.28e+22 -1.08e+23 5.15e+22 5.60e+22 5.15e+22 5.18e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100915160641/index.html |
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:
hp c 0.02 n 3 lp c 0.05 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 90.0 70 80 35 4.67 0.4399 WVFGRD96 91.0 70 80 35 4.67 0.4420 WVFGRD96 92.0 70 80 35 4.67 0.4437 WVFGRD96 93.0 70 80 40 4.67 0.4455 WVFGRD96 94.0 70 80 40 4.68 0.4474 WVFGRD96 95.0 70 80 40 4.68 0.4488 WVFGRD96 96.0 70 80 40 4.68 0.4505 WVFGRD96 97.0 70 80 40 4.68 0.4513 WVFGRD96 98.0 70 80 40 4.68 0.4526 WVFGRD96 99.0 70 80 40 4.68 0.4535 WVFGRD96 100.0 70 80 45 4.69 0.4544 WVFGRD96 101.0 70 80 45 4.69 0.4552 WVFGRD96 102.0 70 80 45 4.69 0.4561 WVFGRD96 103.0 70 75 40 4.70 0.4568 WVFGRD96 104.0 70 75 40 4.70 0.4576 WVFGRD96 105.0 70 75 40 4.70 0.4585 WVFGRD96 106.0 70 75 45 4.70 0.4594 WVFGRD96 107.0 70 75 45 4.70 0.4602 WVFGRD96 108.0 70 75 45 4.70 0.4608 WVFGRD96 109.0 70 75 45 4.71 0.4616 WVFGRD96 110.0 70 75 45 4.71 0.4620 WVFGRD96 111.0 70 75 45 4.71 0.4624 WVFGRD96 112.0 70 75 45 4.71 0.4625 WVFGRD96 113.0 70 75 50 4.71 0.4628 WVFGRD96 114.0 70 75 50 4.71 0.4629 WVFGRD96 115.0 70 75 50 4.71 0.4634 WVFGRD96 116.0 70 75 50 4.71 0.4633 WVFGRD96 117.0 70 75 50 4.71 0.4636 WVFGRD96 118.0 70 75 50 4.72 0.4633 WVFGRD96 119.0 70 75 50 4.72 0.4632 WVFGRD96 120.0 70 75 50 4.72 0.4631 WVFGRD96 121.0 70 75 55 4.72 0.4627 WVFGRD96 122.0 70 75 55 4.72 0.4625 WVFGRD96 123.0 70 75 55 4.72 0.4623 WVFGRD96 124.0 70 75 55 4.72 0.4621 WVFGRD96 125.0 70 75 55 4.72 0.4614 WVFGRD96 126.0 70 75 55 4.72 0.4614 WVFGRD96 127.0 70 75 55 4.72 0.4604 WVFGRD96 128.0 70 75 55 4.72 0.4601 WVFGRD96 129.0 70 75 55 4.72 0.4593
The best solution is
WVFGRD96 117.0 70 75 50 4.71 0.4636
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
hp c 0.02 n 3 lp c 0.05 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. |
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS 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:
DATE=Thu Sep 16 15:47:23 CDT 2010