2008/04/24 22:47:04 39.533 -119.932 1.0 3.8 Nevada
USGS Felt map for this earthquake
SLU Moment Tensor Solution 2008/04/24 22:47:04 39.533 -119.932 1.0 3.8 Nevada Best Fitting Double Couple Mo = 4.95e+21 dyne-cm Mw = 3.73 Z = 7 km Plane Strike Dip Rake NP1 146 76 164 NP2 240 75 15 Principal Axes: Axis Value Plunge Azimuth T 4.95e+21 21 103 N 0.00e+00 69 284 P -4.95e+21 0 193 Moment Tensor: (dyne-cm) Component Value Mxx -4.48e+21 Mxy -2.03e+21 Mxz -3.42e+20 Myy 3.84e+21 Myz 1.63e+21 Mzz 6.41e+20 -------------- ---------------------- ###------------------------- ####-------------------------- #######--------------------------- ########--------------------------## ##########------------------########## ############------------################ #############-------#################### ###############---######################## ###############-########################## #############----################### ### ##########--------################## T ### #######------------################ ## #####---------------#################### ##-------------------################# ---------------------############### ----------------------############ ----------------------######## -----------------------##### ----- -------------- - P ---------- Harvard Convention Moment Tensor: R T F 6.41e+20 -3.42e+20 -1.63e+21 -3.42e+20 -4.48e+21 2.03e+21 -1.63e+21 2.03e+21 3.84e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080424224704/index.html |
STK = 240 DIP = 75 RAKE = 15 MW = 3.73 HS = 7.0
The waveform inversion is preferred. The surface-wave data do not any depth control
The following compares this source inversion to others
SLU Moment Tensor Solution 2008/04/24 22:47:04 39.533 -119.932 1.0 3.8 Nevada Best Fitting Double Couple Mo = 4.95e+21 dyne-cm Mw = 3.73 Z = 7 km Plane Strike Dip Rake NP1 146 76 164 NP2 240 75 15 Principal Axes: Axis Value Plunge Azimuth T 4.95e+21 21 103 N 0.00e+00 69 284 P -4.95e+21 0 193 Moment Tensor: (dyne-cm) Component Value Mxx -4.48e+21 Mxy -2.03e+21 Mxz -3.42e+20 Myy 3.84e+21 Myz 1.63e+21 Mzz 6.41e+20 -------------- ---------------------- ###------------------------- ####-------------------------- #######--------------------------- ########--------------------------## ##########------------------########## ############------------################ #############-------#################### ###############---######################## ###############-########################## #############----################### ### ##########--------################## T ### #######------------################ ## #####---------------#################### ##-------------------################# ---------------------############### ----------------------############ ----------------------######## -----------------------##### ----- -------------- - P ---------- Harvard Convention Moment Tensor: R T F 6.41e+20 -3.42e+20 -1.63e+21 -3.42e+20 -4.48e+21 2.03e+21 -1.63e+21 2.03e+21 3.84e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080424224704/index.html |
This is a preliminary NCSS moment tensor solution for the event located 3 km ENE of Verdi-Mogul, NV; 39.5252N 119.9228W; Z=2.0km; ML=3.81; (USGS/UCB Joint Notification System) on 04/24/2008 22:47:04:390 UTC. Other information about this event can be viewed at: http://earthquake.usgs.gov/recenteqsus/Quakes/nc40215976.php Reviewed by: Rick UCB Seismological Laboratory Inversion method: complete waveform Stations used: NN.BEK BK.ORV BK.CMB Berkeley Moment Tensor Solution Best Fitting Double-Couple: Mo = 5.10E+21 Dyne-cm Mw = 3.74 Z = 5 km Plane Strike Rake Dip NP1 236 -11 81 NP2 328 -171 79 Event Date/Time: 04/24/2008 22:47:04:390 Event ID: 40215976 ----------- ----------------------- ------------------------------- ####--------------------------------- ########--------------------------------- ############--------------------------------- ##############--------------------------------- #################-------------------------------- ####################--------------------------####### #######################---------------------########### ########################----------------############### ###########################-----------################### ###########################------######################## T ############################--########################### ############################-############################ ###########################------########################## #########################----------########################## ######################-------------######################## ###################-----------------####################### #################--------------------###################### ###############-----------------------##################### ###########---------------------------################### ########------------------------------################# ######---------------------------------################ ####-----------------------------------############## -------------------------------------############ -------------------------------------########## -------------------------------------######## -------------- -------------------##### ------------ P -------------------### --------- ------------------- ----------------------- ----------- Lower Hemisphere Equiangle Projection Deviatoric Solution: Principal Axes: Axis Value Plunge Azimuth T 5.028 2 282 N 0.089 76 19 P -5.117 14 191 Source Composition: Type Percent DC 96.5 CLVD 3.5 Iso 0.0 Moment Tensor: Scale = 10**21 Dyne-cm Component Value Mxx -4.413 Mxy -1.918 Mxz 1.248 Myy 4.634 Myz 0.090 Mzz -0.220 ----------- ----------------------- ------------------------------- ####--------------------------------- ########--------------------------------- ############--------------------------------- ##############--------------------------------- #################-------------------------------- #####################-------------------------####### #######################--------------------############ #########################---------------############### ###########################----------#################### #############################---######################### T ######################################################### ######################################################### #############################--############################ ##########################--------########################### ######################-------------######################## ####################----------------####################### #################--------------------###################### ###############-----------------------##################### ############--------------------------################### ########------------------------------################# ######---------------------------------################ ####-----------------------------------############## --------------------------------------########### -------------------------------------########## -------------------------------------######## -------------- -------------------##### ------------ P -------------------### --------- ------------------- ----------------------- ----------- Lower Hemisphere Equiangle Projection |
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 0.10 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 60 80 15 3.51 0.4731 WVFGRD96 1.0 240 80 10 3.53 0.5030 WVFGRD96 2.0 240 80 10 3.61 0.5798 WVFGRD96 3.0 240 80 10 3.64 0.6083 WVFGRD96 4.0 240 75 10 3.67 0.6207 WVFGRD96 5.0 240 75 15 3.69 0.6272 WVFGRD96 6.0 240 75 15 3.71 0.6308 WVFGRD96 7.0 240 75 15 3.73 0.6326 WVFGRD96 8.0 240 75 20 3.76 0.6324 WVFGRD96 9.0 240 80 25 3.78 0.6305 WVFGRD96 10.0 240 80 25 3.79 0.6285 WVFGRD96 11.0 240 80 20 3.80 0.6265 WVFGRD96 12.0 240 80 20 3.81 0.6228 WVFGRD96 13.0 240 80 15 3.82 0.6181 WVFGRD96 14.0 60 75 15 3.83 0.6140 WVFGRD96 15.0 60 75 15 3.84 0.6076 WVFGRD96 16.0 60 75 10 3.85 0.5997 WVFGRD96 17.0 60 75 10 3.86 0.5902 WVFGRD96 18.0 60 75 10 3.87 0.5790 WVFGRD96 19.0 60 75 10 3.88 0.5662 WVFGRD96 20.0 60 75 10 3.89 0.5519 WVFGRD96 21.0 60 75 10 3.89 0.5363 WVFGRD96 22.0 60 75 10 3.90 0.5198 WVFGRD96 23.0 60 75 10 3.91 0.5025 WVFGRD96 24.0 60 75 10 3.91 0.4844 WVFGRD96 25.0 60 75 10 3.91 0.4662 WVFGRD96 26.0 60 75 10 3.92 0.4478 WVFGRD96 27.0 60 70 5 3.92 0.4300 WVFGRD96 28.0 60 70 5 3.93 0.4122 WVFGRD96 29.0 60 70 5 3.93 0.3953
The best solution is
WVFGRD96 7.0 240 75 15 3.73 0.6326
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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was
hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2
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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. |
The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES STK= 239.99 DIP= 75.00 RAKE= 24.99 OR STK= 143.11 DIP= 65.91 RAKE= 163.53 DEPTH = 17.0 km Mw = 3.92 Best Fit 0.8279 - P-T axis plot gives solutions with FIT greater than FIT90
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az Dist First motion
Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.
Digital data were collected, instrument response removed and traces converted
to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh- and Love-wave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.
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Pressure-tension axis trends. Since the surface-wave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. |
Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled. |
The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used
Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.
The fits to the waveforms with the given mechanism are show below:
This figure shows the fit to the three components of motion (Z - vertical, R-radial and T - transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:
hp c 0.02 n 3 lp c 0.10 n 3
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=Fri Apr 25 21:56:54 CDT 2008