Location
2015/01/20 21:42:33 41.895 -119.630 10.0 3.5 Nevada
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports main page
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2015/01/20 21:42:33:0 41.90 -119.63 10.0 3.5 Nevada
Stations used:
NC.KRMB NN.PAH NN.PNT US.WVOR UW.BLOW UW.TREE
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.95e+21 dyne-cm
Mw = 3.58
Z = 10 km
Plane Strike Dip Rake
NP1 25 85 -55
NP2 122 35 -171
Principal Axes:
Axis Value Plunge Azimuth
T 2.95e+21 31 87
N 0.00e+00 35 202
P -2.95e+21 40 327
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.22e+21
Mxy 9.23e+20
Mxz -1.14e+21
Myy 1.64e+21
Myz 2.10e+21
Mzz -4.20e+20
--------------
-------------------###
----------------------######
----------------------########
--------- ------------##########
---------- P -----------############
#---------- ----------##############
##----------------------################
##---------------------#################
###---------------------########## #####
####-------------------########### T #####
#####-----------------############ #####
######---------------#####################
######-------------#####################
#######-----------######################
########--------######################
#########-----######################
###########-#####################-
#########----###############--
#######---------------------
###-------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-4.20e+20 -1.14e+21 -2.10e+21
-1.14e+21 -1.22e+21 -9.23e+20
-2.10e+21 -9.23e+20 1.64e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150120214233/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 25
DIP = 85
RAKE = -55
MW = 3.58
HS = 10.0
The NDK file is 20150120214233.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
UNR |
USGS/SLU Moment Tensor Solution
ENS 2015/01/20 21:42:33:0 41.90 -119.63 10.0 3.5 Nevada
Stations used:
NC.KRMB NN.PAH NN.PNT US.WVOR UW.BLOW UW.TREE
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.95e+21 dyne-cm
Mw = 3.58
Z = 10 km
Plane Strike Dip Rake
NP1 25 85 -55
NP2 122 35 -171
Principal Axes:
Axis Value Plunge Azimuth
T 2.95e+21 31 87
N 0.00e+00 35 202
P -2.95e+21 40 327
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.22e+21
Mxy 9.23e+20
Mxz -1.14e+21
Myy 1.64e+21
Myz 2.10e+21
Mzz -4.20e+20
--------------
-------------------###
----------------------######
----------------------########
--------- ------------##########
---------- P -----------############
#---------- ----------##############
##----------------------################
##---------------------#################
###---------------------########## #####
####-------------------########### T #####
#####-----------------############ #####
######---------------#####################
######-------------#####################
#######-----------######################
########--------######################
#########-----######################
###########-#####################-
#########----###############--
#######---------------------
###-------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-4.20e+20 -1.14e+21 -2.10e+21
-1.14e+21 -1.22e+21 -9.23e+20
-2.10e+21 -9.23e+20 1.64e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150120214233/index.html
|
REVIEWED BY NSL STAFF
Event ID:478221
Origin ID:1217685
Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves
Seismic Moment Tensor Solution
2015/01/20 (020) 21:42:35.00 41.8951 -119.6297 1217685
Depth = 10.0 (km)
Mw = 3.55
Mo = 2.64x10^21 (dyne x cm)
Percent Double Couple = 99 %
Percent CLVD = 1 %
no ISO calculated
Epsilon=0.01
Percent Variance Reduction = 59.48 %
Total Fit = 25.69
Major Double Couple
strike dip rake
Nodal Plane 1: 176 33 -85
Nodal Plane 2: 350 58 -93
DEVIATORIC MOMENT TENSOR
Moment Tensor Elements: Spherical Coordinates
Mrr= -2.39 Mtt= 0.05 Mff= 2.34
Mrt= 0.27 Mrf= -1.09 Mtf= -0.29 EXP=21
Moment Tensor Elements: Cartesian Coordinates
0.05 0.29 0.27
0.29 2.34 1.09
0.27 1.09 -2.39
Eigenvalues:
T-axis eigenvalue= 2.63
N-axis eigenvalue= 0.02
P-axis eigenvalue= -2.64
Eigenvalues and eigenvectors of the Major Double Couple:
T-axis ev= 2.63 trend=82 plunge=13
N-axis ev= 0.00 trend=352 plunge=3
P-axis ev=-2.63 trend=250 plunge=77
Maximum Azmuithal Gap=217 Distance to Nearest Station= 55.4 (km)
Number of Stations (D=Displacement/V=Velocity) Used=2 (defining only)
MOD.BK.D WVOR.US.D
##################
########---##############
########-------##############
########-----------##############
#######--------------###############
#######----------------###############
-#######------------------###############
########------------------###############
########--------------------###############
########---------------------########## #
#######----------------------########## T ##
#######------- -------------######### ##
#######------- P -------------##############
########------ -------------##############
########----------------------#############
#########---------------------#############
########---------------------############
########--------------------############
#########------------------############
########-----------------###########
#########--------------##########
#########-----------#########
##########-------########
###########-######
#
All Stations defining and nondefining:
Station.Net Def Distance Azi Bazi lo-f hi-f vmodel
(km) (deg) (deg) (Hz) (Hz)
MOD.BK (D) Y 55.4 271 90 0.020 0.080 MOD.BK.wus.glib
WVOR.US (D) Y 100.9 54 234 0.020 0.080 WVOR.US.wus.glib
(V)-velocity (D)-Displacement
Author: www-data
Date: 2015/01/20 22:49:12
mtinv Version 2.1_DEVEL OCT2008
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Magnitudes
mLg Magnitude
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
ML Magnitude
(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.
Context
The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).
Waveform Inversion
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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Location of broadband stations used for waveform inversion
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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:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
br c 0.12 0.25 n 4 p 2
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 20 75 15 3.35 0.3560
WVFGRD96 2.0 25 70 25 3.44 0.4192
WVFGRD96 3.0 200 90 -40 3.50 0.4121
WVFGRD96 4.0 205 90 -60 3.57 0.4510
WVFGRD96 5.0 25 90 55 3.56 0.4806
WVFGRD96 6.0 25 85 -65 3.56 0.4906
WVFGRD96 7.0 25 85 -60 3.54 0.4982
WVFGRD96 8.0 25 85 -65 3.60 0.5021
WVFGRD96 9.0 210 90 60 3.59 0.5031
WVFGRD96 10.0 25 85 -55 3.58 0.5044
WVFGRD96 11.0 205 90 50 3.60 0.5039
WVFGRD96 12.0 25 85 -50 3.59 0.5027
WVFGRD96 13.0 210 80 45 3.61 0.5022
WVFGRD96 14.0 210 80 45 3.61 0.5003
WVFGRD96 15.0 210 80 45 3.62 0.4968
WVFGRD96 16.0 205 85 40 3.64 0.4924
WVFGRD96 17.0 210 75 40 3.64 0.4880
WVFGRD96 18.0 210 75 40 3.65 0.4833
WVFGRD96 19.0 210 75 40 3.66 0.4782
WVFGRD96 20.0 210 75 40 3.67 0.4736
WVFGRD96 21.0 210 75 40 3.68 0.4682
WVFGRD96 22.0 210 75 40 3.69 0.4624
WVFGRD96 23.0 210 75 40 3.69 0.4560
WVFGRD96 24.0 210 75 40 3.70 0.4492
WVFGRD96 25.0 210 75 40 3.71 0.4425
WVFGRD96 26.0 210 75 40 3.72 0.4351
WVFGRD96 27.0 210 75 40 3.72 0.4275
WVFGRD96 28.0 210 75 40 3.73 0.4198
WVFGRD96 29.0 210 75 40 3.74 0.4119
The best solution is
WVFGRD96 10.0 25 85 -55 3.58 0.5044
The mechanism correspond to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
|
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Figure 2. Depth sensitivity for waveform mechanism
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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
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
br c 0.12 0.25 n 4 p 2
|
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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.
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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.
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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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Discussion
Acknowledgements
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.
Velocity Model
The WUS model 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
Quality Control
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
Last Changed Mon Dec 7 00:00:15 CST 2015
