Location

Location ANSS

2021/08/16 23:58:56 45.43 16.27 10.0 4.7 Croatia

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2021/08/16 23:58:56:0 45.43 16.27 10.0 4.7 Croatia Stations used: BW.BE1 BW.BGDS BW.BHG BW.KW1 BW.MGS03 BW.MGS05 BW.PART BW.RTBE BW.SCE BW.UH3 CH.FUORN CZ.CKRC CZ.KRUC CZ.STAC CZ.TREC CZ.VRAC CZ.ZVC GR.GEC2 GR.GEC7 GR.WET HU.BUD HU.KOVH HU.MORH HU.SOP MN.BLY OE.ABTA OE.ARSA OE.BIOA OE.CONA OE.CSNA OE.FETA OE.KBA OE.LESA OE.MOA OE.MOTA OE.MYKA OE.OBKA OE.RETA OE.RONA OE.SOKA OE.SQTA OE.VIE OE.WATA SJ.BBLS SJ.FRGS SK.MODS SL.BOJS SL.CADS SL.CEY SL.CRES SL.DOBS SL.GBAS SL.GCIS SL.GOLS SL.GORS SL.GROS SL.JAVS SL.KNDS SL.KOGS SL.LJU SL.MOZS SL.PDKS SL.PERS SL.ROBS SL.SKDS SL.VISS SL.VNDS SL.VOJS SL.ZAVS Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.19e+22 dyne-cm Mw = 4.16 Z = 12 km Plane Strike Dip Rake NP1 75 70 40 NP2 329 53 155 Principal Axes: Axis Value Plunge Azimuth T 2.19e+22 42 298 N 0.00e+00 46 97 P -2.19e+22 11 198 Moment Tensor: (dyne-cm) Component Value Mxx -1.63e+22 Mxy -1.14e+22 Mxz 8.92e+21 Myy 7.27e+21 Myz -8.32e+21 Mzz 9.04e+21 -------------- ##-------------------- ###########----------------- ###############--------------- ###################--------------- ######################-------------- ####### ###############------------- ######## T ################------------- ######## #################-----------# ##############################--------#### ###############################-----###### ################################-######### #############################---########## ######################----------######## ----#########-------------------######## -------------------------------####### ------------------------------###### -----------------------------##### ---------------------------### ------ -----------------## --- P ---------------- ------------ Global CMT Convention Moment Tensor: R T P 9.04e+21 8.92e+21 8.32e+21 8.92e+21 -1.63e+22 1.14e+22 8.32e+21 1.14e+22 7.27e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20210816235856/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 = 75
      DIP = 70
     RAKE = 40
       MW = 4.16
       HS = 12.0

The NDK file is 20210816235856.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU OTHER

USGS/SLU Moment Tensor Solution ENS 2021/08/16 23:58:56:0 45.43 16.27 10.0 4.7 Croatia Stations used: BW.BE1 BW.BGDS BW.BHG BW.KW1 BW.MGS03 BW.MGS05 BW.PART BW.RTBE BW.SCE BW.UH3 CH.FUORN CZ.CKRC CZ.KRUC CZ.STAC CZ.TREC CZ.VRAC CZ.ZVC GR.GEC2 GR.GEC7 GR.WET HU.BUD HU.KOVH HU.MORH HU.SOP MN.BLY OE.ABTA OE.ARSA OE.BIOA OE.CONA OE.CSNA OE.FETA OE.KBA OE.LESA OE.MOA OE.MOTA OE.MYKA OE.OBKA OE.RETA OE.RONA OE.SOKA OE.SQTA OE.VIE OE.WATA SJ.BBLS SJ.FRGS SK.MODS SL.BOJS SL.CADS SL.CEY SL.CRES SL.DOBS SL.GBAS SL.GCIS SL.GOLS SL.GORS SL.GROS SL.JAVS SL.KNDS SL.KOGS SL.LJU SL.MOZS SL.PDKS SL.PERS SL.ROBS SL.SKDS SL.VISS SL.VNDS SL.VOJS SL.ZAVS Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.19e+22 dyne-cm Mw = 4.16 Z = 12 km Plane Strike Dip Rake NP1 75 70 40 NP2 329 53 155 Principal Axes: Axis Value Plunge Azimuth T 2.19e+22 42 298 N 0.00e+00 46 97 P -2.19e+22 11 198 Moment Tensor: (dyne-cm) Component Value Mxx -1.63e+22 Mxy -1.14e+22 Mxz 8.92e+21 Myy 7.27e+21 Myz -8.32e+21 Mzz 9.04e+21 -------------- ##-------------------- ###########----------------- ###############--------------- ###################--------------- ######################-------------- ####### ###############------------- ######## T ################------------- ######## #################-----------# ##############################--------#### ###############################-----###### ################################-######### #############################---########## ######################----------######## ----#########-------------------######## -------------------------------####### ------------------------------###### -----------------------------##### ---------------------------### ------ -----------------## --- P ---------------- ------------ Global CMT Convention Moment Tensor: R T P 9.04e+21 8.92e+21 8.32e+21 8.92e+21 -1.63e+22 1.14e+22 8.32e+21 1.14e+22 7.27e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20210816235856/index.html

GEOFON standard1 Time 2021-08-16 23:58:57 Magnitude 4.0 Latitude 45.48°N Longitude 16.25°E Depth 10 km Nodal planes Strike Dip Rake 146° 66° 171° 240° 81° 24°

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

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

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 0.03 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    60    60   -40   3.82 0.4655
WVFGRD96    2.0    60    65   -40   3.93 0.5598
WVFGRD96    3.0    65    75   -35   3.97 0.5648
WVFGRD96    4.0    70    85    45   4.03 0.5807
WVFGRD96    5.0    75    75    45   4.05 0.6349
WVFGRD96    6.0    75    75    45   4.07 0.6815
WVFGRD96    7.0    75    70    40   4.08 0.7170
WVFGRD96    8.0    75    75    45   4.13 0.7420
WVFGRD96    9.0    75    70    45   4.14 0.7632
WVFGRD96   10.0    75    70    40   4.15 0.7777
WVFGRD96   11.0    75    70    40   4.16 0.7857
WVFGRD96   12.0    75    70    40   4.16 0.7878
WVFGRD96   13.0    75    65    40   4.17 0.7858
WVFGRD96   14.0    70    75    35   4.17 0.7814
WVFGRD96   15.0    70    75    35   4.18 0.7745
WVFGRD96   16.0    70    70    35   4.19 0.7657
WVFGRD96   17.0    70    70    35   4.19 0.7552
WVFGRD96   18.0    70    70    35   4.20 0.7432
WVFGRD96   19.0    70    70    35   4.21 0.7301
WVFGRD96   20.0    70    70    35   4.21 0.7160
WVFGRD96   21.0    70    70    35   4.22 0.7026
WVFGRD96   22.0    70    70    35   4.23 0.6870
WVFGRD96   23.0    70    70    35   4.23 0.6710
WVFGRD96   24.0    70    70    35   4.24 0.6545
WVFGRD96   25.0    70    70    30   4.25 0.6380
WVFGRD96   26.0    70    70    30   4.26 0.6212
WVFGRD96   27.0    70    70    30   4.26 0.6043
WVFGRD96   28.0    70    70    30   4.27 0.5870
WVFGRD96   29.0    70    65    30   4.27 0.5697

The best solution is

WVFGRD96   12.0    75    70    40   4.16 0.7878

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 0.03 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.

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

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:

Last Changed Tue Aug 17 09:30:35 CDT 2021