2011/08/24 00:04:36 37.912 -77.950 7 4.20 Virginia
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/08/24 00:04:36:0 37.91 -77.95 7.0 4.2 Virginia Stations used: CO.HODGE CO.JSC IU.SSPA LD.BRNJ LD.LUPA LD.MVL LD.PAL LD.SDMD LD.WVNY PE.PSUB TA.KMSC US.ACSO US.BINY US.BLA US.CBN US.CNNC US.ERPA US.MCWV US.NHSC US.TZTN Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 5.69e+21 dyne-cm Mw = 3.77 Z = 6 km Plane Strike Dip Rake NP1 40 60 109 NP2 185 35 60 Principal Axes: Axis Value Plunge Azimuth T 5.69e+21 69 350 N 0.00e+00 17 210 P -5.69e+21 13 116 Moment Tensor: (dyne-cm) Component Value Mxx -3.18e+20 Mxy 2.01e+21 Mxz 2.47e+21 Myy -4.31e+21 Myz -1.48e+21 Mzz 4.63e+21 -----######### ------################ -------####################- ------#######################- -------########################--- -------########################----- -------#########################------ --------########## ###########-------- -------########### T ###########-------- --------########### ##########---------- -------########################----------- -------#######################------------ -------#####################-------------- -------###################-------------- -------#################----------- -- -------##############------------- P - ------############--------------- ------#########------------------- -----####--------------------- --####---------------------- ####------------------ ###----------- Global CMT Convention Moment Tensor: R T P 4.63e+21 2.47e+21 1.48e+21 2.47e+21 -3.18e+20 -2.01e+21 1.48e+21 -2.01e+21 -4.31e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110824000436/index.html |
STK = 185 DIP = 35 RAKE = 60 MW = 3.77 HS = 6.0
The NDK file is 20110824000436.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/08/24 00:04:36:0 37.91 -77.95 7.0 4.2 Virginia Stations used: CO.HODGE CO.JSC IU.SSPA LD.BRNJ LD.LUPA LD.MVL LD.PAL LD.SDMD LD.WVNY PE.PSUB TA.KMSC US.ACSO US.BINY US.BLA US.CBN US.CNNC US.ERPA US.MCWV US.NHSC US.TZTN Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 5.69e+21 dyne-cm Mw = 3.77 Z = 6 km Plane Strike Dip Rake NP1 40 60 109 NP2 185 35 60 Principal Axes: Axis Value Plunge Azimuth T 5.69e+21 69 350 N 0.00e+00 17 210 P -5.69e+21 13 116 Moment Tensor: (dyne-cm) Component Value Mxx -3.18e+20 Mxy 2.01e+21 Mxz 2.47e+21 Myy -4.31e+21 Myz -1.48e+21 Mzz 4.63e+21 -----######### ------################ -------####################- ------#######################- -------########################--- -------########################----- -------#########################------ --------########## ###########-------- -------########### T ###########-------- --------########### ##########---------- -------########################----------- -------#######################------------ -------#####################-------------- -------###################-------------- -------#################----------- -- -------##############------------- P - ------############--------------- ------#########------------------- -----####--------------------- --####---------------------- ####------------------ ###----------- Global CMT Convention Moment Tensor: R T P 4.63e+21 2.47e+21 1.48e+21 2.47e+21 -3.18e+20 -2.01e+21 1.48e+21 -2.01e+21 -4.31e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110824000436/index.html |
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
(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:
hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 185 10 45 3.99 0.4378 WVFGRD96 1.0 190 15 50 3.91 0.4465 WVFGRD96 2.0 185 20 50 3.84 0.4691 WVFGRD96 3.0 185 25 55 3.81 0.4980 WVFGRD96 4.0 185 30 55 3.79 0.5239 WVFGRD96 5.0 185 30 60 3.79 0.5361 WVFGRD96 6.0 185 35 60 3.77 0.5362 WVFGRD96 7.0 185 35 60 3.76 0.5257 WVFGRD96 8.0 180 35 55 3.75 0.5123 WVFGRD96 9.0 175 35 45 3.73 0.4983 WVFGRD96 10.0 175 35 45 3.75 0.4998 WVFGRD96 11.0 150 40 -20 3.71 0.4893 WVFGRD96 12.0 150 45 -20 3.70 0.4903 WVFGRD96 13.0 150 45 -20 3.71 0.4907 WVFGRD96 14.0 150 45 -15 3.71 0.4895 WVFGRD96 15.0 150 45 -15 3.72 0.4869 WVFGRD96 16.0 150 45 -15 3.72 0.4831 WVFGRD96 17.0 150 45 -15 3.73 0.4782 WVFGRD96 18.0 150 50 -15 3.72 0.4735 WVFGRD96 19.0 150 50 -15 3.73 0.4680 WVFGRD96 20.0 150 45 -15 3.75 0.4623 WVFGRD96 21.0 150 45 -15 3.76 0.4556 WVFGRD96 22.0 150 45 -15 3.77 0.4483 WVFGRD96 23.0 150 50 -15 3.76 0.4413 WVFGRD96 24.0 150 50 -15 3.77 0.4351 WVFGRD96 25.0 150 50 -15 3.77 0.4286 WVFGRD96 26.0 150 50 -15 3.78 0.4214 WVFGRD96 27.0 150 50 -15 3.79 0.4141 WVFGRD96 28.0 150 50 -15 3.80 0.4081 WVFGRD96 29.0 150 50 -15 3.80 0.4015
The best solution is
WVFGRD96 6.0 185 35 60 3.77 0.5362
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 0.06 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 CUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 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: