Location
2018/08/16 18:19:04 41.88 14.88 9.0 5.1 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 2018/08/16 18:19:04:0 41.88 14.88 9.0 5.1 Gropparella
Stations used:
IV.AMUR IV.BSSO IV.BULG IV.CERA IV.CERT IV.CESX IV.CMPR
IV.FIAM IV.GATE IV.GUMA IV.LPEL IV.MA9 IV.MGR IV.MIDA
IV.MIGL IV.MSAG IV.NOCI IV.NRCA IV.PALZ IV.PIGN IV.POFI
IV.PTQR IV.RNI2 IV.SGG IV.SGRT IV.TOLF IV.VAGA
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 0.06 n 3
Best Fitting Double Couple
Mo = 6.92e+23 dyne-cm
Mw = 5.16
Z = 18 km
Plane Strike Dip Rake
NP1 278 85 155
NP2 10 65 5
Principal Axes:
Axis Value Plunge Azimuth
T 6.92e+23 21 231
N 0.00e+00 65 88
P -6.92e+23 14 327
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.15e+23
Mxy 5.95e+23
Mxz -2.80e+23
Myy 1.69e+23
Myz -8.87e+22
Mzz 4.62e+22
-----------###
-------------######
--- P --------------########
---- --------------#########
------------------------##########
-------------------------###########
--------------------------############
---------------------------#############
---------------------------#############
#####-----------------------##############
#######################-----##############
###########################-------########
###########################--------------#
#########################---------------
#########################---------------
##### ###############---------------
#### T ###############--------------
### ##############--------------
#################-------------
###############-------------
##########------------
#####---------
Global CMT Convention Moment Tensor:
R T P
4.62e+22 -2.80e+23 8.87e+22
-2.80e+23 -2.15e+23 -5.95e+23
8.87e+22 -5.95e+23 1.69e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20180816181904/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 = 10
DIP = 65
RAKE = 5
MW = 5.16
HS = 18.0
The NDK file is 20180816181904.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
INGVTDMT |
SLU Moment Tensor Solution
ENS 2018/08/16 18:19:04:0 41.88 14.88 9.0 5.1 Gropparella
Stations used:
IV.AMUR IV.BSSO IV.BULG IV.CERA IV.CERT IV.CESX IV.CMPR
IV.FIAM IV.GATE IV.GUMA IV.LPEL IV.MA9 IV.MGR IV.MIDA
IV.MIGL IV.MSAG IV.NOCI IV.NRCA IV.PALZ IV.PIGN IV.POFI
IV.PTQR IV.RNI2 IV.SGG IV.SGRT IV.TOLF IV.VAGA
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 0.06 n 3
Best Fitting Double Couple
Mo = 6.92e+23 dyne-cm
Mw = 5.16
Z = 18 km
Plane Strike Dip Rake
NP1 278 85 155
NP2 10 65 5
Principal Axes:
Axis Value Plunge Azimuth
T 6.92e+23 21 231
N 0.00e+00 65 88
P -6.92e+23 14 327
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.15e+23
Mxy 5.95e+23
Mxz -2.80e+23
Myy 1.69e+23
Myz -8.87e+22
Mzz 4.62e+22
-----------###
-------------######
--- P --------------########
---- --------------#########
------------------------##########
-------------------------###########
--------------------------############
---------------------------#############
---------------------------#############
#####-----------------------##############
#######################-----##############
###########################-------########
###########################--------------#
#########################---------------
#########################---------------
##### ###############---------------
#### T ###############--------------
### ##############--------------
#################-------------
###############-------------
##########------------
#####---------
Global CMT Convention Moment Tensor:
R T P
4.62e+22 -2.80e+23 8.87e+22
-2.80e+23 -2.15e+23 -5.95e+23
8.87e+22 -5.95e+23 1.69e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20180816181904/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 0.06 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 15 65 20 4.85 0.2399
WVFGRD96 2.0 15 65 15 4.89 0.2743
WVFGRD96 3.0 10 75 0 4.91 0.3036
WVFGRD96 4.0 10 75 -5 4.95 0.3341
WVFGRD96 5.0 10 70 -5 4.99 0.3587
WVFGRD96 6.0 10 70 -5 5.01 0.3734
WVFGRD96 7.0 10 65 0 5.04 0.3822
WVFGRD96 8.0 10 70 5 5.04 0.3879
WVFGRD96 9.0 10 65 5 5.06 0.3946
WVFGRD96 10.0 10 65 5 5.07 0.4009
WVFGRD96 11.0 10 65 5 5.08 0.4073
WVFGRD96 12.0 10 65 5 5.09 0.4131
WVFGRD96 13.0 10 65 5 5.10 0.4184
WVFGRD96 14.0 10 65 5 5.11 0.4235
WVFGRD96 15.0 10 60 5 5.13 0.4276
WVFGRD96 16.0 10 65 5 5.14 0.4297
WVFGRD96 17.0 10 65 5 5.15 0.4309
WVFGRD96 18.0 10 65 5 5.16 0.4314
WVFGRD96 19.0 10 65 5 5.17 0.4307
WVFGRD96 20.0 10 60 5 5.18 0.4289
WVFGRD96 21.0 10 60 5 5.19 0.4281
WVFGRD96 22.0 10 60 5 5.20 0.4265
WVFGRD96 23.0 10 60 5 5.21 0.4240
WVFGRD96 24.0 10 60 5 5.22 0.4216
WVFGRD96 25.0 10 60 5 5.22 0.4185
WVFGRD96 26.0 5 60 0 5.24 0.4158
WVFGRD96 27.0 5 60 0 5.25 0.4140
WVFGRD96 28.0 5 60 0 5.26 0.4121
WVFGRD96 29.0 5 65 0 5.28 0.4108
The best solution is
WVFGRD96 18.0 10 65 5 5.16 0.4314
The mechanism correspond to the best fit is
|
|
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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 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.
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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
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=Thu Aug 16 16:58:36 CDT 2018
Last Changed 2018/08/16
