Location

2015/08/24 03:43:54 44.20 11.94 9.0 3.5 Italy

Arrival Times (from USGS)

Felt Map

Focal Mechanism

SLU Moment Tensor Solution ENS 2015/08/24 03:43:54:0 44.20 11.94 9.0 3.5 Italy Stations used: GU.MAIM IV.AOI IV.ARCI IV.ARVD IV.ASQU IV.BDI IV.CAFI IV.CELB IV.CESI IV.CESX IV.CING IV.FDMO IV.GROG IV.MSSA IV.MTRZ IV.MURB IV.PARC IV.PESA IV.PIEI IV.PLMA IV.ROVR IV.SACS IV.SALO IV.SNTG MN.AQU MN.VLC Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 2.95e+21 dyne-cm Mw = 3.58 Z = 18 km Plane Strike Dip Rake NP1 26 72 154 NP2 125 65 20 Principal Axes: Axis Value Plunge Azimuth T 2.95e+21 31 344 N 0.00e+00 58 174 P -2.95e+21 5 77 Moment Tensor: (dyne-cm) Component Value Mxx 1.84e+21 Mxy -1.22e+21 Mxz 1.20e+21 Myy -2.62e+21 Myz -5.88e+20 Mzz 7.73e+20 ############## ####################-- ######### ###########----- ########## T ###########------ ############ ###########-------- -##########################--------- ---########################----------- -----#######################---------- ------#####################----------- P ---------##################------------ ----------#################--------------- ------------##############---------------- --------------###########----------------- ----------------#######----------------- ------------------####------------------ -------------------------------------- -----------------#######------------ ---------------################--# -----------################### ---------################### ---################### ############## Global CMT Convention Moment Tensor: R T P 7.73e+20 1.20e+21 5.88e+20 1.20e+21 1.84e+21 1.22e+21 5.88e+20 1.22e+21 -2.62e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20150824034354/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 = 125
      DIP = 65
     RAKE = 20
       MW = 3.58
       HS = 18.0

The NDK file is 20150824034354.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

SLU Moment Tensor Solution ENS 2015/08/24 03:43:54:0 44.20 11.94 9.0 3.5 Italy Stations used: GU.MAIM IV.AOI IV.ARCI IV.ARVD IV.ASQU IV.BDI IV.CAFI IV.CELB IV.CESI IV.CESX IV.CING IV.FDMO IV.GROG IV.MSSA IV.MTRZ IV.MURB IV.PARC IV.PESA IV.PIEI IV.PLMA IV.ROVR IV.SACS IV.SALO IV.SNTG MN.AQU MN.VLC Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 2.95e+21 dyne-cm Mw = 3.58 Z = 18 km Plane Strike Dip Rake NP1 26 72 154 NP2 125 65 20 Principal Axes: Axis Value Plunge Azimuth T 2.95e+21 31 344 N 0.00e+00 58 174 P -2.95e+21 5 77 Moment Tensor: (dyne-cm) Component Value Mxx 1.84e+21 Mxy -1.22e+21 Mxz 1.20e+21 Myy -2.62e+21 Myz -5.88e+20 Mzz 7.73e+20 ############## ####################-- ######### ###########----- ########## T ###########------ ############ ###########-------- -##########################--------- ---########################----------- -----#######################---------- ------#####################----------- P ---------##################------------ ----------#################--------------- ------------##############---------------- --------------###########----------------- ----------------#######----------------- ------------------####------------------ -------------------------------------- -----------------#######------------ ---------------################--# -----------################### ---------################### ---################### ############## Global CMT Convention Moment Tensor: R T P 7.73e+20 1.20e+21 5.88e+20 1.20e+21 1.84e+21 1.22e+21 5.88e+20 1.22e+21 -2.62e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20150824034354/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.

Location of broadband stations used for waveform inversion

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 0.02 n 3 
lp c 0.10 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   125    85     0   3.18 0.2888
WVFGRD96    2.0   125    80     0   3.27 0.3156
WVFGRD96    3.0   120    80   -15   3.33 0.3113
WVFGRD96    4.0   120    80   -10   3.37 0.3016
WVFGRD96    5.0   125    65     0   3.40 0.2968
WVFGRD96    6.0   125    60    15   3.38 0.3083
WVFGRD96    7.0   125    60    15   3.40 0.3384
WVFGRD96    8.0   115    60    30   3.38 0.3815
WVFGRD96    9.0   115    60    30   3.40 0.4187
WVFGRD96   10.0   125    65    20   3.44 0.4526
WVFGRD96   11.0   125    65    20   3.46 0.4828
WVFGRD96   12.0   125    65    25   3.47 0.5087
WVFGRD96   13.0   125    65    20   3.49 0.5311
WVFGRD96   14.0   125    70    20   3.52 0.5493
WVFGRD96   15.0   125    65    20   3.55 0.5623
WVFGRD96   16.0   125    65    25   3.56 0.5721
WVFGRD96   17.0   125    65    25   3.57 0.5788
WVFGRD96   18.0   125    65    20   3.58 0.5817
WVFGRD96   19.0   125    65    20   3.59 0.5812
WVFGRD96   20.0   125    65    20   3.60 0.5774
WVFGRD96   21.0   125    65    20   3.61 0.5699
WVFGRD96   22.0   125    65    20   3.62 0.5599
WVFGRD96   23.0   125    65    20   3.63 0.5463
WVFGRD96   24.0   125    65    20   3.64 0.5297
WVFGRD96   25.0   125    65    15   3.64 0.5108
WVFGRD96   26.0   125    65    15   3.65 0.4908
WVFGRD96   27.0   125    65    15   3.66 0.4693
WVFGRD96   28.0   125    60    10   3.65 0.4463
WVFGRD96   29.0   125    60   -10   3.65 0.4301

The best solution is

WVFGRD96   18.0   125    65    20   3.58 0.5817

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:

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 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 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.

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=Mon Aug 24 06:41:01 CDT 2015

Last Changed 2015/08/24