2008/05/08 05:55:02 39.539 -119.915 3 3.8 Nevada
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/05/08 05:55:02 39.539 -119.915 3 3.8 Nevada
Best Fitting Double Couple
Mo = 3.16e+21 dyne-cm
Mw = 3.60
Z = 11 km
Plane Strike Dip Rake
NP1 25 85 -20
NP2 117 70 -175
Principal Axes:
Axis Value Plunge Azimuth
T 3.16e+21 10 73
N 0.00e+00 69 192
P -3.16e+21 18 339
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.23e+21
Mxy 1.83e+21
Mxz -6.85e+20
Myy 2.42e+21
Myz 8.56e+20
Mzz -1.88e+20
--------------
--- -------------###
------ P -------------######
------- ------------########
------------------------##########
------------------------############
#-----------------------###########
###---------------------############ T #
#####------------------############# #
########----------------##################
##########-------------###################
#############---------####################
###############------#####################
##################-#####################
##################----##################
################----------############
##############----------------------
############----------------------
#########---------------------
#######---------------------
###-------------------
--------------
Harvard Convention
Moment Tensor:
R T F
-1.88e+20 -6.85e+20 -8.56e+20
-6.85e+20 -2.23e+21 -1.83e+21
-8.56e+20 -1.83e+21 2.42e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080508055502/index.html
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STK = 25
DIP = 85
RAKE = -20
MW = 3.60
HS = 11.0
The waveform inversion is preferred even though there is not much depth sensitivity. The frequency passband is very low frequency to overcome rapid changes in wave propagation that mitigate against the use of a single wave propagation model. The focal mechanism is such that there is not much depth control from the surface-waves either.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/05/08 05:55:02 39.539 -119.915 3 3.8 Nevada
Best Fitting Double Couple
Mo = 3.16e+21 dyne-cm
Mw = 3.60
Z = 11 km
Plane Strike Dip Rake
NP1 25 85 -20
NP2 117 70 -175
Principal Axes:
Axis Value Plunge Azimuth
T 3.16e+21 10 73
N 0.00e+00 69 192
P -3.16e+21 18 339
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.23e+21
Mxy 1.83e+21
Mxz -6.85e+20
Myy 2.42e+21
Myz 8.56e+20
Mzz -1.88e+20
--------------
--- -------------###
------ P -------------######
------- ------------########
------------------------##########
------------------------############
#-----------------------###########
###---------------------############ T #
#####------------------############# #
########----------------##################
##########-------------###################
#############---------####################
###############------#####################
##################-#####################
##################----##################
################----------############
##############----------------------
############----------------------
#########---------------------
#######---------------------
###-------------------
--------------
Harvard Convention
Moment Tensor:
R T F
-1.88e+20 -6.85e+20 -8.56e+20
-6.85e+20 -2.23e+21 -1.83e+21
-8.56e+20 -1.83e+21 2.42e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080508055502/index.html
|
This is a preliminary NCSS moment tensor solution for the event located
5 km NE of Verdi-Mogul, NV; 39.5415N 119.9168W; Z=2.5km; ML=3.54;
(USGS/UCB Joint Notification System) on 05/08/2008 05:55:01:760 UTC.
Other information about this event can be viewed at:
RECEIVED Thu, 8 May 2008 17:52:28 -0500 (CDT)
Reviewed by:
Peggy
UCB Seismological Laboratory
Inversion method: complete waveform
Stations used: NN.BEK BK.ORV BK.CMB BK.HELL
Berkeley Moment Tensor Solution
Best Fitting Double-Couple:
Mo = 3.40E+21 Dyne-cm
Mw = 3.62
Z = 5 km
Plane Strike Rake Dip
NP1 118 -167 82
NP2 26 -8 77
Event Date/Time: 05/08/2008 05:55:01:760
Event ID: 51202333
-----------
-----------------------
------ --------------------##
--------- P -------------------######
----------- -------------------########
-----------------------------------##########
-----------------------------------############
------------------------------------#############
-------------------------------------################
##-----------------------------------##################
#####--------------------------------##################
########-----------------------------####################
############-------------------------######################
###############----------------------######################
##################------------------#######################
#####################--------------########################
#########################----------##########################
###########################------##########################
###############################-###########################
###############################---#########################
# ##########################--------#####################
T #########################--------------###############
########################-------------------##########
#########################-------------------------#####
#######################------------------------------
####################-----------------------------
#################------------------------------
###############------------------------------
############-----------------------------
########-----------------------------
###----------------------------
-----------------------
-----------
Lower Hemisphere Equiangle Projection
Deviatoric Solution:
Principal Axes:
Axis Value Plunge Azimuth
T 3.227 3 252
N 0.288 75 149
P -3.516 14 343
Source Composition:
Type Percent
DC 83.6
CLVD 16.4
Iso 0.0
Moment Tensor: Scale = 10**21 Dyne-cm
Component Value
Mxx -2.707
Mxy 1.847
Mxz -0.925
Myy 2.640
Myz 0.099
Mzz 0.066
-----------
-----------------------
------- -------------------##
---------- P -------------------#####
------------ -------------------#######
-----------------------------------##########
------------------------------------###########
------------------------------------#############
-------------------------------------################
##------------------------------------#################
####---------------------------------##################
########-----------------------------####################
############-------------------------######################
###############---------------------#######################
###################---------------#########################
#######################---------###########################
#############################################################
###########################################################
###########################################################
###########################################################
# #######################################################
T ##############################-----###################
##########################----------------###########
##########################-------------------------####
########################-----------------------------
####################-----------------------------
#################------------------------------
###############------------------------------
###########------------------------------
#######------------------------------
##-----------------------------
-----------------------
-----------
Lower Hemisphere Equiangle Projection
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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 0.5 205 90 5 3.29 0.3975
WVFGRD96 1.0 205 90 5 3.32 0.4268
WVFGRD96 2.0 25 90 0 3.40 0.5142
WVFGRD96 3.0 205 90 10 3.44 0.5493
WVFGRD96 4.0 25 85 -15 3.47 0.5699
WVFGRD96 5.0 25 80 -20 3.50 0.5824
WVFGRD96 6.0 25 80 -20 3.52 0.5930
WVFGRD96 7.0 205 90 20 3.53 0.5975
WVFGRD96 8.0 25 80 -25 3.57 0.6170
WVFGRD96 9.0 25 80 -25 3.59 0.6186
WVFGRD96 10.0 25 85 -25 3.59 0.6199
WVFGRD96 11.0 25 85 -20 3.60 0.6199
WVFGRD96 12.0 25 85 -20 3.61 0.6193
WVFGRD96 13.0 25 85 -20 3.62 0.6177
WVFGRD96 14.0 25 90 -20 3.63 0.6161
WVFGRD96 15.0 205 85 20 3.63 0.6155
WVFGRD96 16.0 205 80 20 3.64 0.6138
WVFGRD96 17.0 205 80 20 3.65 0.6111
WVFGRD96 18.0 205 80 20 3.65 0.6066
WVFGRD96 19.0 25 90 -15 3.67 0.5971
WVFGRD96 20.0 25 90 -15 3.67 0.5921
WVFGRD96 21.0 25 90 -15 3.68 0.5860
WVFGRD96 22.0 25 90 -15 3.69 0.5796
WVFGRD96 23.0 205 80 15 3.69 0.5732
WVFGRD96 24.0 25 80 15 3.70 0.5660
WVFGRD96 25.0 25 80 15 3.71 0.5594
WVFGRD96 26.0 25 80 15 3.71 0.5526
WVFGRD96 27.0 25 80 15 3.72 0.5452
WVFGRD96 28.0 25 80 15 3.73 0.5375
WVFGRD96 29.0 25 80 15 3.73 0.5296
The best solution is
WVFGRD96 11.0 25 85 -20 3.60 0.6199
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 0.05 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. |
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= 21.87
DIP= 68.52
RAKE= -32.50
OR
STK= 124.99
DIP= 60.00
RAKE= -154.99
DEPTH = 4.0 km
Mw = 3.63
Best Fit 0.8812 - P-T axis plot gives solutions with FIT greater than FIT90
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The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) 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. |
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| 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
Sta Az(deg) Dist(km) ORV 271 136 CMB 194 172 GASB 274 241 BDM 225 244 WDC 298 252 CVS 240 257 MOD 353 264 BRIB 228 265 BKS 228 274 HOPS 258 279 MHC 212 287 MCCM 240 300 PACP 204 306 TIN 151 313 HELL 166 327 SAO 204 336 WVOR 18 339 YBH 317 339 HAST 203 378 JCC 293 378 PKD 188 403 ELK 70 420 HUMO 324 426 RAMR 191 441 ISA 163 449 ARV 169 499 GSC 149 545 BGU 73 606 DUG 81 612 MWC 164 613 COR 334 627 HLID 44 640 BBR 155 643 LDF 138 644 RVR 159 656 NLU 84 673 BEL 149 707 HWUT 69 743 SRU 90 811 AHID 61 822 RRI2 57 833 DCID1 55 856 REDW 58 868 WUAZ 118 876 SNOW 57 879 DLMT 40 883 IMW 54 889 LOHW 57 898 BW06 64 940 MSO 29 944 NEW 12 995 TUC 132 1149 ISCO 84 1226 ANMO 109 1297
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:
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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 0.05 n 3
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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 May 8 17:57:00 CDT 2008