The ANSS event ID is nn00263178 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00263178/executive.
2008/10/18 02:27:38 36.175 -114.522 0.0 3.4 Nevada
USGS/SLU Moment Tensor Solution
ENS 2008/10/18 02:27:38:0 36.17 -114.52 0.0 3.4 Nevada
Stations used:
BK.CMB CI.BAR CI.GLA CI.GSC CI.ISA CI.LDF II.PFO TA.Q14A
TA.R11A TA.R13A TA.R16A TA.S16A TA.U13A TA.U14A TA.U15A
TA.U16A TA.V14A TA.V15A TA.V17A TA.W13A TA.W14A TA.W15A
TA.W16A TA.W17A TA.W18A TA.X14A TA.X15A TA.X16A TA.Y12C
TA.Y13A TA.Y15A TA.Y16A TA.Z13A TA.Z15A TA.Z16A US.DUG
UU.BGU UU.SRU
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.64e+21 dyne-cm
Mw = 3.41
Z = 7 km
Plane Strike Dip Rake
NP1 205 81 150
NP2 300 60 10
Principal Axes:
Axis Value Plunge Azimuth
T 1.64e+21 27 158
N 0.00e+00 59 11
P -1.64e+21 14 256
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.03e+21
Mxy -8.06e+20
Mxz -5.27e+20
Myy -1.27e+21
Myz 6.28e+20
Mzz 2.47e+20
##############
###################---
####################--------
####################----------
#####################-------------
-------------########---------------
-------------------##-----------------
---------------------###----------------
--------------------#######-------------
--------------------##########------------
-------------------#############----------
------------------################--------
-- ------------###################------
- P ------------####################----
- -----------######################---
-------------#######################--
-----------#########################
----------########### ##########
-------############ T ########
------############ #######
--####################
##############
Global CMT Convention Moment Tensor:
R T P
2.47e+20 -5.27e+20 -6.28e+20
-5.27e+20 1.03e+21 8.06e+20
-6.28e+20 8.06e+20 -1.27e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081018022738/index.html
|
STK = 300
DIP = 60
RAKE = 10
MW = 3.41
HS = 7.0
The NDK file is 20081018022738.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
 |
The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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 3 br c 0.12 0.25 n 4 p 2 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 295 75 -20 3.22 0.4412
WVFGRD96 1.0 295 75 -15 3.23 0.4639
WVFGRD96 2.0 295 75 -20 3.30 0.5279
WVFGRD96 3.0 295 70 -15 3.33 0.5445
WVFGRD96 4.0 295 70 -15 3.35 0.5508
WVFGRD96 5.0 300 60 10 3.39 0.5529
WVFGRD96 6.0 300 60 10 3.40 0.5553
WVFGRD96 7.0 300 60 10 3.41 0.5554
WVFGRD96 8.0 300 55 10 3.44 0.5548
WVFGRD96 9.0 300 60 10 3.44 0.5512
WVFGRD96 10.0 300 60 10 3.45 0.5473
WVFGRD96 11.0 300 60 10 3.46 0.5426
WVFGRD96 12.0 300 60 10 3.47 0.5371
WVFGRD96 13.0 295 65 -10 3.47 0.5316
WVFGRD96 14.0 300 75 25 3.48 0.5261
WVFGRD96 15.0 300 75 25 3.48 0.5260
WVFGRD96 16.0 300 75 20 3.49 0.5249
WVFGRD96 17.0 300 75 20 3.50 0.5241
WVFGRD96 18.0 300 75 20 3.51 0.5222
WVFGRD96 19.0 300 75 20 3.52 0.5193
WVFGRD96 20.0 300 75 20 3.52 0.5156
WVFGRD96 21.0 300 75 20 3.53 0.5118
WVFGRD96 22.0 300 75 20 3.54 0.5074
WVFGRD96 23.0 300 75 20 3.55 0.5022
WVFGRD96 24.0 300 75 15 3.55 0.4965
WVFGRD96 25.0 300 75 15 3.56 0.4907
WVFGRD96 26.0 295 90 20 3.57 0.4848
WVFGRD96 27.0 295 90 20 3.57 0.4789
WVFGRD96 28.0 295 90 20 3.58 0.4729
WVFGRD96 29.0 295 90 20 3.59 0.4668
WVFGRD96 30.0 295 90 20 3.60 0.4606
WVFGRD96 31.0 295 90 20 3.60 0.4540
WVFGRD96 32.0 295 90 20 3.61 0.4474
WVFGRD96 33.0 295 90 20 3.62 0.4405
WVFGRD96 34.0 295 90 15 3.63 0.4334
WVFGRD96 35.0 295 90 15 3.64 0.4265
WVFGRD96 36.0 295 90 15 3.65 0.4192
WVFGRD96 37.0 295 90 15 3.67 0.4118
WVFGRD96 38.0 295 90 15 3.68 0.4036
WVFGRD96 39.0 300 80 15 3.69 0.3953
WVFGRD96 40.0 300 75 20 3.72 0.3853
WVFGRD96 41.0 300 75 20 3.73 0.3789
WVFGRD96 42.0 300 75 20 3.74 0.3724
WVFGRD96 43.0 300 75 20 3.74 0.3665
WVFGRD96 44.0 300 75 20 3.75 0.3607
WVFGRD96 45.0 300 75 20 3.76 0.3549
WVFGRD96 46.0 300 75 20 3.76 0.3491
WVFGRD96 47.0 300 75 15 3.77 0.3433
WVFGRD96 48.0 300 75 15 3.77 0.3377
WVFGRD96 49.0 300 75 15 3.78 0.3322
WVFGRD96 50.0 300 75 15 3.78 0.3268
The best solution is
WVFGRD96 7.0 300 60 10 3.41 0.5554
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 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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 br c 0.12 0.25 n 4 p 2 br c 0.12 0.25 n 4 p 2
|
| Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
|
| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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