Location
2018/08/14 21:48:31 41.85 14.84 19.0 4.6 Gropparella
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports page for
Focal Mechanism
SLU Moment Tensor Solution
ENS 2018/08/14 21:48:31:0 41.85 14.84 19.0 4.6 Gropparella
Stations used:
IV.AMUR IV.BSSO IV.CERA IV.FIAM IV.LPEL IV.MELA IV.MGR
IV.MSAG IV.NRCA IV.PIGN IV.PTQR IV.RMP IV.RNI2 IV.SACR
IV.SGG IV.SGRT IV.SNAL IV.TRIV
Filtering commands used:
cut o DIST/3.3 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
Best Fitting Double Couple
Mo = 8.71e+22 dyne-cm
Mw = 4.56
Z = 12 km
Plane Strike Dip Rake
NP1 132 80 165
NP2 225 75 10
Principal Axes:
Axis Value Plunge Azimuth
T 8.71e+22 18 88
N 0.00e+00 72 281
P -8.71e+22 4 179
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.66e+22
Mxy 3.78e+21
Mxz 6.44e+21
Myy 7.91e+22
Myz 2.50e+22
Mzz 7.56e+21
--------------
----------------------
----------------------------
---------------------------###
###-----------------------########
#####-------------------############
########---------------###############
##########-----------###################
############-------#####################
###############---################### ##
################-#################### T ##
###############---################### ##
#############-------######################
###########-----------##################
##########--------------################
#######------------------#############
#####----------------------#########
###--------------------------#####
#-----------------------------
----------------------------
---------- ---------
------ P -----
Global CMT Convention Moment Tensor:
R T P
7.56e+21 6.44e+21 -2.50e+22
6.44e+21 -8.66e+22 -3.78e+21
-2.50e+22 -3.78e+21 7.91e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20180814214831/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 = 225
DIP = 75
RAKE = 10
MW = 4.56
HS = 12.0
The NDK file is 20180814214831.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
INGVTDMT |
SLU Moment Tensor Solution
ENS 2018/08/14 21:48:31:0 41.85 14.84 19.0 4.6 Gropparella
Stations used:
IV.AMUR IV.BSSO IV.CERA IV.FIAM IV.LPEL IV.MELA IV.MGR
IV.MSAG IV.NRCA IV.PIGN IV.PTQR IV.RMP IV.RNI2 IV.SACR
IV.SGG IV.SGRT IV.SNAL IV.TRIV
Filtering commands used:
cut o DIST/3.3 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
Best Fitting Double Couple
Mo = 8.71e+22 dyne-cm
Mw = 4.56
Z = 12 km
Plane Strike Dip Rake
NP1 132 80 165
NP2 225 75 10
Principal Axes:
Axis Value Plunge Azimuth
T 8.71e+22 18 88
N 0.00e+00 72 281
P -8.71e+22 4 179
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.66e+22
Mxy 3.78e+21
Mxz 6.44e+21
Myy 7.91e+22
Myz 2.50e+22
Mzz 7.56e+21
--------------
----------------------
----------------------------
---------------------------###
###-----------------------########
#####-------------------############
########---------------###############
##########-----------###################
############-------#####################
###############---################### ##
################-#################### T ##
###############---################### ##
#############-------######################
###########-----------##################
##########--------------################
#######------------------#############
#####----------------------#########
###--------------------------#####
#-----------------------------
----------------------------
---------- ---------
------ P -----
Global CMT Convention Moment Tensor:
R T P
7.56e+21 6.44e+21 -2.50e+22
6.44e+21 -8.66e+22 -3.78e+21
-2.50e+22 -3.78e+21 7.91e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20180814214831/index.html
|
|
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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 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 1.0 225 75 10 4.29 0.2738
WVFGRD96 2.0 225 70 10 4.36 0.3202
WVFGRD96 3.0 225 75 10 4.40 0.3571
WVFGRD96 4.0 225 75 5 4.44 0.3906
WVFGRD96 5.0 225 70 10 4.48 0.4174
WVFGRD96 6.0 225 70 10 4.50 0.4337
WVFGRD96 7.0 225 70 10 4.52 0.4439
WVFGRD96 8.0 225 75 10 4.52 0.4492
WVFGRD96 9.0 225 75 10 4.53 0.4534
WVFGRD96 10.0 225 75 10 4.54 0.4562
WVFGRD96 11.0 225 75 10 4.55 0.4580
WVFGRD96 12.0 225 75 10 4.56 0.4586
WVFGRD96 13.0 225 75 10 4.57 0.4570
WVFGRD96 14.0 225 80 15 4.59 0.4563
WVFGRD96 15.0 225 75 15 4.60 0.4563
WVFGRD96 16.0 225 75 15 4.61 0.4539
WVFGRD96 17.0 225 75 15 4.62 0.4500
WVFGRD96 18.0 225 75 15 4.63 0.4459
WVFGRD96 19.0 225 80 20 4.64 0.4409
WVFGRD96 20.0 225 80 20 4.65 0.4358
WVFGRD96 21.0 225 80 20 4.66 0.4304
WVFGRD96 22.0 225 80 25 4.66 0.4237
WVFGRD96 23.0 225 80 25 4.67 0.4186
WVFGRD96 24.0 225 80 25 4.68 0.4119
WVFGRD96 25.0 225 80 25 4.69 0.4051
WVFGRD96 26.0 225 80 25 4.70 0.3983
WVFGRD96 27.0 225 80 25 4.71 0.3918
WVFGRD96 28.0 225 80 25 4.72 0.3851
WVFGRD96 29.0 40 85 -20 4.74 0.3779
The best solution is
WVFGRD96 12.0 225 75 10 4.56 0.4586
The mechanism correspond to the best fit is
|
|
Figure 1. Waveform inversion focal mechanism
|
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
|
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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
|
|
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.
Discussion
Velocity Model
The nnCIA used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01
C.It. A. Di Luzio et al Earth Plan Lettrs 280 (2009) 1-12 Fig 5. 7-8 MODEL/SURF3
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
1.5000 3.7497 2.1436 2.2753 0.500E-02 0.100E-01 0.00 0.00 1.00 1.00
3.0000 4.9399 2.8210 2.4858 0.500E-02 0.100E-01 0.00 0.00 1.00 1.00
3.0000 6.0129 3.4336 2.7058 0.500E-02 0.100E-01 0.00 0.00 1.00 1.00
7.0000 5.5516 3.1475 2.6093 0.167E-02 0.333E-02 0.00 0.00 1.00 1.00
15.0000 5.8805 3.3583 2.6770 0.167E-02 0.333E-02 0.00 0.00 1.00 1.00
6.0000 7.1059 4.0081 3.0002 0.167E-02 0.333E-02 0.00 0.00 1.00 1.00
8.0000 7.1000 3.9864 3.0120 0.167E-02 0.333E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.4036 3.2760 0.167E-02 0.333E-02 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:
DATE=Tue Aug 14 20:11:29 CDT 2018
Last Changed 2018/08/14
