Location

2016/08/24 01:36:32 42.7060 13.2230 4.2 6.00

SLU Moment Tensor Solution ENS 2016/08/24 01:36:32:0 42.71 13.22 4.2 6.0 Stations used: IV.ARCI IV.CERT IV.CESX IV.FIAM IV.GIUL IV.GUAR IV.GUMA IV.MA9 IV.MCIV IV.PTQR IV.RMP IV.SACS IV.SNTG IV.SRES Filtering commands used: hp c 0.01 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.14e+25 dyne-cm Mw = 5.97 Z = 5 km Plane Strike Dip Rake NP1 155 50 -85 NP2 327 40 -96 Principal Axes: Axis Value Plunge Azimuth T 1.14e+25 5 241 N 0.00e+00 4 332 P -1.14e+25 84 100 Moment Tensor: (dyne-cm) Component Value Mxx 2.57e+24 Mxy 4.75e+24 Mxz -2.53e+23 Myy 8.57e+24 Myz -2.05e+24 Mzz -1.11e+25 ############## #----################# ####----------############## ####--------------############ #####------------------########### ######--------------------########## #######---------------------########## ########-----------------------######### ########------------------------######## ##########-----------------------######### ##########------------- --------######## ###########------------ P ---------####### ###########------------ ---------####### ###########-----------------------###### ############----------------------###### #########---------------------##### T ###########-------------------#### ############------------------### #############---------------## ##############------------## ###############------- ############## Global CMT Convention Moment Tensor: R T P -1.11e+25 -2.53e+23 2.05e+24 -2.53e+23 2.57e+24 -4.75e+24 2.05e+24 -4.75e+24 8.57e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20160824013632/index.html

Preferred Solution

      STK = 155
      DIP = 50
     RAKE = -85
       MW = 5.97
       HS = 5.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU	GCMT	INGVTDMT
SLU Moment Tensor Solution ENS 2016/08/24 01:36:32:0 42.71 13.22 4.2 6.0 Stations used: IV.ARCI IV.CERT IV.CESX IV.FIAM IV.GIUL IV.GUAR IV.GUMA IV.MA9 IV.MCIV IV.PTQR IV.RMP IV.SACS IV.SNTG IV.SRES Filtering commands used: hp c 0.01 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.14e+25 dyne-cm Mw = 5.97 Z = 5 km Plane Strike Dip Rake NP1 155 50 -85 NP2 327 40 -96 Principal Axes: Axis Value Plunge Azimuth T 1.14e+25 5 241 N 0.00e+00 4 332 P -1.14e+25 84 100 Moment Tensor: (dyne-cm) Component Value Mxx 2.57e+24 Mxy 4.75e+24 Mxz -2.53e+23 Myy 8.57e+24 Myz -2.05e+24 Mzz -1.11e+25 ############## #----################# ####----------############## ####--------------############ #####------------------########### ######--------------------########## #######---------------------########## ########-----------------------######### ########------------------------######## ##########-----------------------######### ##########------------- --------######## ###########------------ P ---------####### ###########------------ ---------####### ###########-----------------------###### ############----------------------###### #########---------------------##### T ###########-------------------#### ############------------------### #############---------------## ##############------------## ###############------- ############## Global CMT Convention Moment Tensor: R T P -1.11e+25 -2.53e+23 2.05e+24 -2.53e+23 2.57e+24 -4.75e+24 2.05e+24 -4.75e+24 8.57e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20160824013632/index.html	August 24, 2016, CENTRAL ITALY, MW=6.2 Howard Koss CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C201608240136A DATA: II IU LD CU G IC GE DK XF KP MN L.P.BODY WAVES:150S, 338C, T= 40 MANTLE WAVES: 131S, 213C, T=125 SURFACE WAVES: 165S, 429C, T= 50 TIMESTAMP: Q-20160824053527 CENTROID LOCATION: ORIGIN TIME: 01:36:38.1 0.1 LAT:42.66N 0.00;LON: 13.20E 0.00 DEP: 12.0 FIX;TRIANG HDUR: 3.1 MOMENT TENSOR: SCALE 10**25 D-CM RR=-2.490 0.010; TT= 0.523 0.011 PP= 1.960 0.010; RT=-0.384 0.031 RP=-0.339 0.029; TP=-1.040 0.009 PRINCIPAL AXES: 1.(T) VAL= 2.509;PLG= 1;AZM= 63 2.(N) 0.074; 11; 153 3.(P) -2.589; 79; 325 BEST DBLE.COUPLE:M0= 2.55*10**25 NP1: STRIKE=142;DIP=45;SLIP=-106 NP2: STRIKE=343;DIP=47;SLIP= -75 --######### ----------######### #-------------######### ##----------------######## ###-----------------####### T ####------------------###### ####--------- -------######## #####--------- P --------######## ######-------- --------######## #######------------------######## ########------------------####### ########-----------------###### #########---------------####### ##########-------------###### ###########-----------##### #############------#### ################--- ##########-

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:

hp c 0.01 n 3
lp c 0.05 n 3

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   170    50   -65   5.78 0.5617
WVFGRD96    2.0   165    50   -70   5.83 0.6245
WVFGRD96    3.0   155    50   -85   5.89 0.6674
WVFGRD96    4.0   150    50   -90   5.93 0.6769
WVFGRD96    5.0   155    50   -85   5.97 0.7180
WVFGRD96    6.0   150    50   -90   5.97 0.6555
WVFGRD96    7.0   155    55   -85   5.96 0.5650
WVFGRD96    8.0   195    75   -30   5.85 0.5025
WVFGRD96    9.0   195    70    35   5.86 0.5123
WVFGRD96   10.0   195    70    35   5.87 0.5232
WVFGRD96   11.0   195    70    35   5.88 0.5316
WVFGRD96   12.0   195    70    35   5.88 0.5378
WVFGRD96   13.0   195    70    35   5.89 0.5437
WVFGRD96   14.0   195    70    35   5.90 0.5485
WVFGRD96   15.0   190    70    40   5.92 0.5481

The best solution is

WVFGRD96    5.0   155    50   -85   5.97 0.7180

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

hp c 0.01 n 3
lp c 0.05 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)

 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=Fri Aug 26 07:47:38 CDT 2016