2009/04/07 17:47:38 42.3490 13.4050 10.0 5.50 CENTRAL ITALY
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/04/07 17:47:38:0 42.35 13.40 10.0 5.5 CENTRAL ITALY
Stations used:
CH.FUORN CH.SENIN GE.MATE GE.PSZ HU.BUD HU.PKSM HU.SOP
IU.GRFO MN.BNI MN.CEL MN.CUC MN.PDG MN.TIP MN.TRI MN.TUE
MN.VLC MN.VTS RO.BZS
Filtering commands used:
hp c 0.0125 n 3
lp c 0.025 n 3
Best Fitting Double Couple
Mo = 1.70e+24 dyne-cm
Mw = 5.42
Z = 29 km
Plane Strike Dip Rake
NP1 345 60 -40
NP2 98 56 -143
Principal Axes:
Axis Value Plunge Azimuth
T 1.70e+24 2 42
N 0.00e+00 42 134
P -1.70e+24 48 310
Moment Tensor: (dyne-cm)
Component Value
Mxx 6.27e+23
Mxy 1.21e+24
Mxz -4.87e+23
Myy 3.19e+23
Myz 6.96e+23
Mzz -9.45e+23
---###########
---------#############
--------------############ T
-----------------##########
--------------------##############
----------------------##############
--------- ------------##############
---------- P -------------##############
---------- --------------#############
----------------------------##############
##---------------------------#############
###--------------------------#############
#####------------------------#############
#######----------------------#########--
###########------------------######-----
#################---------------------
###########################---------
#########################---------
#######################-------
#####################-------
##################----
#############-
Global CMT Convention Moment Tensor:
R T P
-9.45e+23 -4.87e+23 -6.96e+23
-4.87e+23 6.27e+23 -1.21e+24
-6.96e+23 -1.21e+24 3.19e+23
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20090407174738/index.html
|
STK = 345
DIP = 60
RAKE = -40
MW = 5.42
HS = 29.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/04/07 17:47:38:0 42.35 13.40 10.0 5.5 CENTRAL ITALY
Stations used:
CH.FUORN CH.SENIN GE.MATE GE.PSZ HU.BUD HU.PKSM HU.SOP
IU.GRFO MN.BNI MN.CEL MN.CUC MN.PDG MN.TIP MN.TRI MN.TUE
MN.VLC MN.VTS RO.BZS
Filtering commands used:
hp c 0.0125 n 3
lp c 0.025 n 3
Best Fitting Double Couple
Mo = 1.70e+24 dyne-cm
Mw = 5.42
Z = 29 km
Plane Strike Dip Rake
NP1 345 60 -40
NP2 98 56 -143
Principal Axes:
Axis Value Plunge Azimuth
T 1.70e+24 2 42
N 0.00e+00 42 134
P -1.70e+24 48 310
Moment Tensor: (dyne-cm)
Component Value
Mxx 6.27e+23
Mxy 1.21e+24
Mxz -4.87e+23
Myy 3.19e+23
Myz 6.96e+23
Mzz -9.45e+23
---###########
---------#############
--------------############ T
-----------------##########
--------------------##############
----------------------##############
--------- ------------##############
---------- P -------------##############
---------- --------------#############
----------------------------##############
##---------------------------#############
###--------------------------#############
#####------------------------#############
#######----------------------#########--
###########------------------######-----
#################---------------------
###########################---------
#########################---------
#######################-------
#####################-------
##################----
#############-
Global CMT Convention Moment Tensor:
R T P
-9.45e+23 -4.87e+23 -6.96e+23
-4.87e+23 6.27e+23 -1.21e+24
-6.96e+23 -1.21e+24 3.19e+23
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20090407174738/index.html
|
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.
|
|
|
|
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:
hp c 0.0125 n 3 lp c 0.025 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 175 80 -30 5.10 0.2029
WVFGRD96 1.0 175 80 -25 5.10 0.2113
WVFGRD96 2.0 -5 85 15 5.11 0.2297
WVFGRD96 3.0 -5 85 15 5.14 0.2421
WVFGRD96 4.0 -5 85 15 5.16 0.2505
WVFGRD96 5.0 -5 85 15 5.18 0.2547
WVFGRD96 6.0 -5 85 15 5.20 0.2572
WVFGRD96 7.0 -5 90 10 5.21 0.2574
WVFGRD96 8.0 -5 85 15 5.23 0.2564
WVFGRD96 9.0 345 45 -30 5.33 0.2666
WVFGRD96 10.0 340 40 -35 5.35 0.2800
WVFGRD96 11.0 340 45 -40 5.35 0.2942
WVFGRD96 12.0 340 45 -40 5.36 0.3085
WVFGRD96 13.0 340 60 -55 5.38 0.3238
WVFGRD96 14.0 340 60 -55 5.39 0.3393
WVFGRD96 15.0 340 55 -50 5.39 0.3524
WVFGRD96 16.0 340 55 -50 5.39 0.3651
WVFGRD96 17.0 340 55 -50 5.39 0.3758
WVFGRD96 18.0 340 55 -45 5.39 0.3846
WVFGRD96 19.0 340 55 -45 5.39 0.3935
WVFGRD96 20.0 340 55 -45 5.39 0.4000
WVFGRD96 21.0 340 55 -45 5.40 0.4074
WVFGRD96 22.0 340 55 -45 5.41 0.4126
WVFGRD96 23.0 340 55 -45 5.41 0.4163
WVFGRD96 24.0 345 60 -40 5.41 0.4198
WVFGRD96 25.0 345 60 -40 5.41 0.4230
WVFGRD96 26.0 345 60 -40 5.41 0.4252
WVFGRD96 27.0 345 60 -40 5.41 0.4271
WVFGRD96 28.0 345 60 -40 5.42 0.4280
WVFGRD96 29.0 345 60 -40 5.42 0.4284
The best solution is
WVFGRD96 29.0 345 60 -40 5.42 0.4284
The mechanism correspond 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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was
hp c 0.0125 n 3 lp c 0.025 n 3
|
|
|
|
| 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. |
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS 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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Thu Apr 9 18:26:56 MDT 2009