Location
2014/04/14 20:16:47 44.712 -114.218 5.0 3.6 Idaho
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 2014/04/14 20:16:47:0 44.71 -114.22 5.0 3.6 Idaho
Stations used:
CN.WALA IM.PD31 IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.MFID
IW.REDW IW.SNOW IW.TPAW MB.JTMT TA.H17A UO.PINE US.AHID
US.BMO US.BW06 US.DUG US.EGMT US.ELK US.HAWA US.HWUT
US.LKWY US.MSO US.NEW US.RLMT UU.BGU UU.CTU UU.HVU UU.JLU
UU.MPU UU.NLU UU.RDMU UU.SPU UU.TCU UW.CCRK UW.DAVN UW.DDRF
UW.IRON UW.IZEE UW.LTY UW.OMAK UW.PHIN UW.TREE UW.TUCA
UW.UMAT UW.WOLL
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 4.52e+22 dyne-cm
Mw = 4.37
Z = 9 km
Plane Strike Dip Rake
NP1 296 52 -117
NP2 155 45 -60
Principal Axes:
Axis Value Plunge Azimuth
T 4.52e+22 4 44
N 0.00e+00 21 313
P -4.52e+22 69 144
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.92e+22
Mxy 2.53e+22
Mxz 1.45e+22
Myy 1.99e+22
Myz -6.75e+21
Mzz -3.91e+22
##############
-#####################
---########################
---######################### T
-----######################### #
--####------------##################
######------------------##############
#######---------------------############
#######-----------------------##########
#########------------------------#########
#########--------------------------#######
#########----------------------------#####
##########------------- ------------####
##########------------ P -------------##
###########----------- -------------##
###########---------------------------
###########-------------------------
############----------------------
############------------------
#############---------------
##############--------
##############
Global CMT Convention Moment Tensor:
R T P
-3.91e+22 1.45e+22 6.75e+21
1.45e+22 1.92e+22 -2.53e+22
6.75e+21 -2.53e+22 1.99e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140414201647/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 155
DIP = 45
RAKE = -60
MW = 4.37
HS = 9.0
The NDK file is 20140414201647.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMT |
USGS/SLU Moment Tensor Solution
ENS 2014/04/14 20:16:47:0 44.71 -114.22 5.0 3.6 Idaho
Stations used:
CN.WALA IM.PD31 IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.MFID
IW.REDW IW.SNOW IW.TPAW MB.JTMT TA.H17A UO.PINE US.AHID
US.BMO US.BW06 US.DUG US.EGMT US.ELK US.HAWA US.HWUT
US.LKWY US.MSO US.NEW US.RLMT UU.BGU UU.CTU UU.HVU UU.JLU
UU.MPU UU.NLU UU.RDMU UU.SPU UU.TCU UW.CCRK UW.DAVN UW.DDRF
UW.IRON UW.IZEE UW.LTY UW.OMAK UW.PHIN UW.TREE UW.TUCA
UW.UMAT UW.WOLL
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 4.52e+22 dyne-cm
Mw = 4.37
Z = 9 km
Plane Strike Dip Rake
NP1 296 52 -117
NP2 155 45 -60
Principal Axes:
Axis Value Plunge Azimuth
T 4.52e+22 4 44
N 0.00e+00 21 313
P -4.52e+22 69 144
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.92e+22
Mxy 2.53e+22
Mxz 1.45e+22
Myy 1.99e+22
Myz -6.75e+21
Mzz -3.91e+22
##############
-#####################
---########################
---######################### T
-----######################### #
--####------------##################
######------------------##############
#######---------------------############
#######-----------------------##########
#########------------------------#########
#########--------------------------#######
#########----------------------------#####
##########------------- ------------####
##########------------ P -------------##
###########----------- -------------##
###########---------------------------
###########-------------------------
############----------------------
############------------------
#############---------------
##############--------
##############
Global CMT Convention Moment Tensor:
R T P
-3.91e+22 1.45e+22 6.75e+21
1.45e+22 1.92e+22 -2.53e+22
6.75e+21 -2.53e+22 1.99e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140414201647/index.html
|
Regional Moment Tensor (Mwr)
Moment magnitude derived from a moment tensor
inversion of complete waveforms at regional
distances (less than ~8 degrees), generally
used for the analysis of small to moderate
size earthquakes (typically Mw 3.5-6.0)
crust or upper mantle earthquakes.
Moment
4.75e+15 N-m
Magnitude
4.4
Percent DC
75%
Depth
8.0 km
Updated
2014-04-14 21:01:18 UTC
Author
us
Catalog
us
Contributor
us
Code
us_b000pkhs_mwr
Principal Axes
Axis Value Plunge Azimuth
T 5.034 5 43
N -0.623 8 312
P -4.411 81 165
Nodal Planes
Plane Strike Dip Rake
NP1 305 51 -100
NP2 142 41 -78
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Magnitudes
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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 355 65 -15 4.04 0.3413
WVFGRD96 2.0 355 60 -15 4.12 0.3923
WVFGRD96 3.0 350 60 -25 4.17 0.4214
WVFGRD96 4.0 350 65 -35 4.21 0.4485
WVFGRD96 5.0 350 60 -35 4.23 0.4725
WVFGRD96 6.0 165 50 -40 4.27 0.4930
WVFGRD96 7.0 165 50 -45 4.29 0.5039
WVFGRD96 8.0 155 45 -60 4.36 0.5438
WVFGRD96 9.0 155 45 -60 4.37 0.5440
WVFGRD96 10.0 -5 70 -20 4.29 0.5364
WVFGRD96 11.0 -5 70 -15 4.29 0.5375
WVFGRD96 12.0 -5 75 -15 4.30 0.5373
WVFGRD96 13.0 -5 75 -10 4.31 0.5344
WVFGRD96 14.0 -5 80 -10 4.32 0.5302
WVFGRD96 15.0 180 75 5 4.32 0.5279
WVFGRD96 16.0 180 75 5 4.33 0.5242
WVFGRD96 17.0 180 75 5 4.33 0.5190
WVFGRD96 18.0 180 75 5 4.34 0.5124
WVFGRD96 19.0 180 75 5 4.35 0.5046
WVFGRD96 20.0 180 75 10 4.35 0.4964
WVFGRD96 21.0 180 75 10 4.36 0.4886
WVFGRD96 22.0 180 75 10 4.36 0.4807
WVFGRD96 23.0 180 75 10 4.37 0.4727
WVFGRD96 24.0 180 75 10 4.37 0.4642
WVFGRD96 25.0 180 75 10 4.38 0.4555
WVFGRD96 26.0 180 75 5 4.39 0.4467
WVFGRD96 27.0 180 75 5 4.39 0.4379
WVFGRD96 28.0 180 75 5 4.40 0.4294
WVFGRD96 29.0 180 75 5 4.40 0.4207
The best solution is
WVFGRD96 9.0 155 45 -60 4.37 0.5440
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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
|
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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.
|
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.
Surface-Wave Focal Mechanism
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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Location of broadband stations used to obtain focal mechanism from surface-wave spectral amplitudes
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES
STK= 289.99
DIP= 55.00
RAKE= -125.00
OR
STK= 160.66
DIP= 47.85
RAKE= -50.68
DEPTH = 8.0 km
Mw = 4.42
Best Fit 0.9011 - P-T axis plot gives solutions with FIT greater than FIT90
First motion data
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az Dist First motion
Surface-wave analysis
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.
Data preparation
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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Best mechanism fit as a function of depth. The preferred depth is given above. Lower hemisphere projection
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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.
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Love-wave radiation patterns
Rayleigh-wave radiation patterns
Broadband station distribution
The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used
Waveform comparison for this mechanism
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:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
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.
Appendix A
Spectra fit plots to each station
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 00:11:17 CST 2015
