Location

Location ANSS

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2020/03/22 06:01:20:0 45.87 16.00 10.0 5.0 Croatia Stations used: BW.KW1 BW.MGS04 BW.RTBE GR.CLL GR.GRC3 GR.UBR GR.WET II.XBFO OE.ARSA OE.DAVA OE.KBA OX.ACOM OX.CGRP OX.DRE OX.FUSE OX.PRED OX.SABO PL.NIE SK.MODS 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 0.06 n 3 Best Fitting Double Couple Mo = 7.85e+22 dyne-cm Mw = 4.53 Z = 8 km Plane Strike Dip Rake NP1 210 70 40 NP2 104 53 155 Principal Axes: Axis Value Plunge Azimuth T 7.85e+22 42 73 N 0.00e+00 46 232 P -7.85e+22 11 333 Moment Tensor: (dyne-cm) Component Value Mxx -5.71e+22 Mxy 4.23e+22 Mxz -1.52e+21 Myy 2.46e+22 Myz 4.38e+22 Mzz 3.24e+22 -------------- - P -----------------# ---- --------------####### -------------------########### --------------------############## -------------------################# ------------------#################### ------------------###################### -----------------############# ####### ##---------------############## T ######## ###-------------############### ######## ####-----------########################### ######--------############################ ########----############################ ######################################-- ##########----####################---- ########---------------------------- #######--------------------------- #####------------------------- ####------------------------ #--------------------- -------------- Global CMT Convention Moment Tensor: R T P 3.24e+22 -1.52e+21 -4.38e+22 -1.52e+21 -5.71e+22 -4.23e+22 -4.38e+22 -4.23e+22 2.46e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200322060120/index.html

Preferred Solution

      STK = 210
      DIP = 70
     RAKE = 40
       MW = 4.53
       HS = 8.0

The NDK file is 20200322060120.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU	USGSMWR	OTHER
USGS/SLU Moment Tensor Solution ENS 2020/03/22 06:01:20:0 45.87 16.00 10.0 5.0 Croatia Stations used: BW.KW1 BW.MGS04 BW.RTBE GR.CLL GR.GRC3 GR.UBR GR.WET II.XBFO OE.ARSA OE.DAVA OE.KBA OX.ACOM OX.CGRP OX.DRE OX.FUSE OX.PRED OX.SABO PL.NIE SK.MODS 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 0.06 n 3 Best Fitting Double Couple Mo = 7.85e+22 dyne-cm Mw = 4.53 Z = 8 km Plane Strike Dip Rake NP1 210 70 40 NP2 104 53 155 Principal Axes: Axis Value Plunge Azimuth T 7.85e+22 42 73 N 0.00e+00 46 232 P -7.85e+22 11 333 Moment Tensor: (dyne-cm) Component Value Mxx -5.71e+22 Mxy 4.23e+22 Mxz -1.52e+21 Myy 2.46e+22 Myz 4.38e+22 Mzz 3.24e+22 -------------- - P -----------------# ---- --------------####### -------------------########### --------------------############## -------------------################# ------------------#################### ------------------###################### -----------------############# ####### ##---------------############## T ######## ###-------------############### ######## ####-----------########################### ######--------############################ ########----############################ ######################################-- ##########----####################---- ########---------------------------- #######--------------------------- #####------------------------- ####------------------------ #--------------------- -------------- Global CMT Convention Moment Tensor: R T P 3.24e+22 -1.52e+21 -4.38e+22 -1.52e+21 -5.71e+22 -4.23e+22 -4.38e+22 -4.23e+22 2.46e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200322060120/index.html USGS/SLU Moment Tensor Solution ENS 2020/03/22 06:01:21:0 45.87 16.00 10.0 5.0 Croatia Stations used: BW.KW1 BW.MGS04 BW.RTBE GR.CLL GR.GRC3 GR.UBR GR.WET II.XBFO OE.ARSA OE.DAVA OE.KBA OX.ACOM OX.CGRP OX.DRE OX.FUSE OX.PRED OX.SABO PL.NIE SK.MODS 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 0.06 n 3 Best Fitting Double Couple Mo = 7.85e+22 dyne-cm Mw = 4.53 Z = 8 km Plane Strike Dip Rake NP1 210 70 40 NP2 104 53 155 Principal Axes: Axis Value Plunge Azimuth T 7.85e+22 42 73 N 0.00e+00 46 232 P -7.85e+22 11 333 Moment Tensor: (dyne-cm) Component Value Mxx -5.71e+22 Mxy 4.23e+22 Mxz -1.52e+21 Myy 2.46e+22 Myz 4.38e+22 Mzz 3.24e+22 -------------- - P -----------------# ---- --------------####### -------------------########### --------------------############## -------------------################# ------------------#################### ------------------###################### -----------------############# ####### ##---------------############## T ######## ###-------------############### ######## ####-----------########################### ######--------############################ ########----############################ ######################################-- ##########----####################---- ########---------------------------- #######--------------------------- #####------------------------- ####------------------------ #--------------------- -------------- Global CMT Convention Moment Tensor: R T P 3.24e+22 -1.52e+21 -4.38e+22 -1.52e+21 -5.71e+22 -4.23e+22 -4.38e+22 -4.23e+22 2.46e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200322060121/index.html	Regional Moment Tensor (Mwr) Moment 9.890e+15 N-m Magnitude 4.60 Mwr Depth 4.0 km Percent DC 91% Half Duration - Catalog US Data Source US 1 Contributor US 1 Nodal Planes Plane Strike Dip Rake NP1 246 44 94 NP2 61 46 86 Principal Axes Axis Value Plunge Azimuth T 10.101e+15 N-m 87 261 N -0.435e+15 N-m 3 63 P -9.666e+15 N-m 1 153	EMSC-CSEM

Magnitudes

ML Magnitude

(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

Context

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 0.06 n 3 

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0    40    60    60   4.33 0.3483
WVFGRD96    2.0    40    65    65   4.45 0.4331
WVFGRD96    3.0    45    55    60   4.48 0.4965
WVFGRD96    4.0    50    50    65   4.52 0.5237
WVFGRD96    5.0   215    60    45   4.49 0.5371
WVFGRD96    6.0   215    65    45   4.50 0.5412
WVFGRD96    7.0   210    70    35   4.49 0.5464
WVFGRD96    8.0   210    70    40   4.53 0.5602
WVFGRD96    9.0   210    70    35   4.53 0.5556
WVFGRD96   10.0   205    80    30   4.53 0.5509
WVFGRD96   11.0    20    90   -25   4.53 0.5448
WVFGRD96   12.0    20    90   -25   4.54 0.5405
WVFGRD96   13.0    20    85   -25   4.55 0.5347
WVFGRD96   14.0    20    85   -20   4.56 0.5283
WVFGRD96   15.0    20    85   -20   4.57 0.5219
WVFGRD96   16.0   205    60    20   4.59 0.5168
WVFGRD96   17.0   205    60    20   4.60 0.5177
WVFGRD96   18.0   205    60    20   4.61 0.5180
WVFGRD96   19.0   205    60    20   4.62 0.5173
WVFGRD96   20.0   205    60    20   4.63 0.5156
WVFGRD96   21.0   205    60    20   4.64 0.5130
WVFGRD96   22.0   205    60    20   4.65 0.5100
WVFGRD96   23.0   205    60    20   4.66 0.5063
WVFGRD96   24.0   205    55    15   4.68 0.5021
WVFGRD96   25.0   205    55    15   4.69 0.4973
WVFGRD96   26.0   205    55    15   4.70 0.4921
WVFGRD96   27.0   205    55    15   4.71 0.4865
WVFGRD96   28.0   205    55    15   4.71 0.4799
WVFGRD96   29.0   205    55    15   4.72 0.4725

The best solution is

WVFGRD96    8.0   210    70    40   4.53 0.5602

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 0.06 n 3 

Figure 3. Waveform comparison for selected depth

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.

Discussion

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The WUS.model 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    

Quality Control

Here we tabulate the reasons for not using certain digital data sets

The following stations did not have a valid response files: