2011/08/25 23:40:56 37.967 77.932 8.80 2.70 Virginia
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/08/25 23:40:56:3 37.97 77.93 8.8 2.7 Virginia Stations used: ET.UOM2 ET.UOM3 GS.CVRD GS.SPRD XY.JOSH XY.KEVN Filtering commands used: taper w 0.05 transfer from none to none freqlimtis 0.25 0.30 0.6 1.0 Best Fitting Double Couple Mo = 8.71e+19 dynecm Mw = 2.56 Z = 5 km Plane Strike Dip Rake NP1 66 81 102 NP2 190 15 35 Principal Axes: Axis Value Plunge Azimuth T 8.71e+19 52 350 N 0.00e+00 12 244 P 8.71e+19 35 145 Moment Tensor: (dynecm) Component Value Mxx 7.07e+18 Mxy 2.16e+19 Mxz 7.54e+19 Myy 1.79e+19 Myz 3.06e+19 Mzz 2.50e+19 ########### ################### ######################## ########################### ########### ################# ############ T ################## ############# ################### ################################# ############################### ############################ ######################### ##################### ################# ############# ###### ##  ## P  ##  ## ## ## # Global CMT Convention Moment Tensor: R T P 2.50e+19 7.54e+19 3.06e+19 7.54e+19 7.07e+18 2.16e+19 3.06e+19 2.16e+19 1.79e+19 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110825234056/index.html 
STK = 190 DIP = 15 RAKE = 35 MW = 2.56 HS = 5.0
The NDK file is 20110825234056.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/08/25 23:40:56:3 37.97 77.93 8.8 2.7 Virginia Stations used: ET.UOM2 ET.UOM3 GS.CVRD GS.SPRD XY.JOSH XY.KEVN Filtering commands used: taper w 0.05 transfer from none to none freqlimtis 0.25 0.30 0.6 1.0 Best Fitting Double Couple Mo = 8.71e+19 dynecm Mw = 2.56 Z = 5 km Plane Strike Dip Rake NP1 66 81 102 NP2 190 15 35 Principal Axes: Axis Value Plunge Azimuth T 8.71e+19 52 350 N 0.00e+00 12 244 P 8.71e+19 35 145 Moment Tensor: (dynecm) Component Value Mxx 7.07e+18 Mxy 2.16e+19 Mxz 7.54e+19 Myy 1.79e+19 Myz 3.06e+19 Mzz 2.50e+19 ########### ################### ######################## ########################### ########### ################# ############ T ################## ############# ################### ################################# ############################### ############################ ######################### ##################### ################# ############# ###### ##  ## P  ##  ## ## ## # Global CMT Convention Moment Tensor: R T P 2.50e+19 7.54e+19 3.06e+19 7.54e+19 7.07e+18 2.16e+19 3.06e+19 2.16e+19 1.79e+19 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110825234056/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.

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:
taper w 0.05 transfer from none to none freqlimtis 0.25 0.30 0.6 1.0The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 325 15 10 2.36 0.5438 WVFGRD96 2.0 245 85 75 2.34 0.5999 WVFGRD96 3.0 130 15 25 2.42 0.6503 WVFGRD96 4.0 155 15 0 2.50 0.6706 WVFGRD96 5.0 190 15 35 2.56 0.6845 WVFGRD96 6.0 65 65 75 2.62 0.6835 WVFGRD96 7.0 210 20 70 2.65 0.6539 WVFGRD96 8.0 205 25 70 2.67 0.6222 WVFGRD96 9.0 80 50 90 2.61 0.5901 WVFGRD96 10.0 235 35 90 2.66 0.5813 WVFGRD96 11.0 225 30 75 2.71 0.5887 WVFGRD96 12.0 220 35 75 2.71 0.5877 WVFGRD96 13.0 225 35 75 2.72 0.5717 WVFGRD96 14.0 50 50 90 2.71 0.5567 WVFGRD96 15.0 230 40 90 2.72 0.5374 WVFGRD96 16.0 230 45 95 2.71 0.5124 WVFGRD96 17.0 230 45 95 2.72 0.5007 WVFGRD96 18.0 20 45 70 2.75 0.4943 WVFGRD96 19.0 15 45 65 2.76 0.4821
The best solution is
WVFGRD96 5.0 190 15 35 2.56 0.6845
The mechanism corresponding to the best fit is

The best fit as a function of depth is given in the following figure:

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 observedpredicted 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
taper w 0.05 transfer from none to none freqlimtis 0.25 0.30 0.6 1.0

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 1D 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 0.172E02 0.387E02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E02 0.363E02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E02 0.336E02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E04 0.000E04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E02 0.431E02 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: