Location

Location ANSS

2018/07/04 11:24:20 41.51 19.53 10.0 4.3 Albania

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2018/07/04 11:24:20:7 41.51 19.53 10.0 4.3 Albania Stations used: CL.AGRP CL.MALA CL.ROD3 CL.TRIZ HU.KOVH HU.MORH KO.GADA RO.BAIL RO.BANR RO.BZS RO.COPA RO.DEV RO.GZR RO.HERR RO.LOT RO.MDVR RO.PUNG RO.SIRR RO.VLAD SJ.BBLS 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 = 5.56e+22 dyne-cm Mw = 4.43 Z = 25 km Plane Strike Dip Rake NP1 131 62 112 NP2 270 35 55 Principal Axes: Axis Value Plunge Azimuth T 5.56e+22 66 80 N 0.00e+00 19 300 P -5.56e+22 14 205 Moment Tensor: (dyne-cm) Component Value Mxx -4.28e+22 Mxy -1.83e+22 Mxz 1.56e+22 Myy -4.36e+14 Myz 2.61e+22 Mzz 4.28e+22 -------------- ---------------------- ---------------------------- ------------------------------ #-------##################-------- ###---########################------ ##################################---- ###---###############################--- ##-----###############################-- #--------################ #############- #---------############### T #############- ------------############# ############## --------------############################ --------------########################## -----------------####################### ------------------#################### --------------------################ -----------------------########### ------ --------------------- ----- P -------------------- -- ----------------- -------------- Global CMT Convention Moment Tensor: R T P 4.28e+22 1.56e+22 -2.61e+22 1.56e+22 -4.28e+22 1.83e+22 -2.61e+22 1.83e+22 -4.36e+14 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180704112420/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 = 270
      DIP = 35
     RAKE = 55
       MW = 4.43
       HS = 25.0

The NDK file is 20180704112420.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2018/07/04 11:24:20:7 41.51 19.53 10.0 4.3 Albania Stations used: CL.AGRP CL.MALA CL.ROD3 CL.TRIZ HU.KOVH HU.MORH KO.GADA RO.BAIL RO.BANR RO.BZS RO.COPA RO.DEV RO.GZR RO.HERR RO.LOT RO.MDVR RO.PUNG RO.SIRR RO.VLAD SJ.BBLS 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 = 5.56e+22 dyne-cm Mw = 4.43 Z = 25 km Plane Strike Dip Rake NP1 131 62 112 NP2 270 35 55 Principal Axes: Axis Value Plunge Azimuth T 5.56e+22 66 80 N 0.00e+00 19 300 P -5.56e+22 14 205 Moment Tensor: (dyne-cm) Component Value Mxx -4.28e+22 Mxy -1.83e+22 Mxz 1.56e+22 Myy -4.36e+14 Myz 2.61e+22 Mzz 4.28e+22 -------------- ---------------------- ---------------------------- ------------------------------ #-------##################-------- ###---########################------ ##################################---- ###---###############################--- ##-----###############################-- #--------################ #############- #---------############### T #############- ------------############# ############## --------------############################ --------------########################## -----------------####################### ------------------#################### --------------------################ -----------------------########### ------ --------------------- ----- P -------------------- -- ----------------- -------------- Global CMT Convention Moment Tensor: R T P 4.28e+22 1.56e+22 -2.61e+22 1.56e+22 -4.28e+22 1.83e+22 -2.61e+22 1.83e+22 -4.36e+14 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180704112420/index.html

Magnitudes

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 0.02 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   115    40   -90   4.10 0.4347
WVFGRD96    2.0   115    35   -90   4.18 0.4843
WVFGRD96    3.0   285    50   -90   4.26 0.5128
WVFGRD96    4.0   285    50   -85   4.30 0.4595
WVFGRD96    5.0   305    70   -55   4.29 0.3824
WVFGRD96    6.0   305    80   -50   4.28 0.3784
WVFGRD96    7.0   135    90    50   4.27 0.3940
WVFGRD96    8.0   310    85   -60   4.33 0.4141
WVFGRD96    9.0   135    90    60   4.33 0.4361
WVFGRD96   10.0   310    90   -60   4.32 0.4572
WVFGRD96   11.0   135    85    55   4.34 0.4771
WVFGRD96   12.0   135    80    55   4.35 0.4962
WVFGRD96   13.0   140    75    55   4.36 0.5133
WVFGRD96   14.0   145    70    60   4.38 0.5305
WVFGRD96   15.0   150    65    65   4.40 0.5466
WVFGRD96   16.0   150    65    70   4.41 0.5617
WVFGRD96   17.0   150    65    70   4.41 0.5746
WVFGRD96   18.0   150    65    70   4.42 0.5849
WVFGRD96   19.0   150    60    70   4.43 0.5933
WVFGRD96   20.0   155    60    75   4.44 0.5999
WVFGRD96   21.0   275    35    60   4.41 0.6066
WVFGRD96   22.0   275    35    60   4.41 0.6138
WVFGRD96   23.0   275    35    60   4.42 0.6181
WVFGRD96   24.0   275    35    60   4.42 0.6199
WVFGRD96   25.0   270    35    55   4.43 0.6201
WVFGRD96   26.0   260    40    50   4.44 0.6194
WVFGRD96   27.0   260    40    45   4.45 0.6178
WVFGRD96   28.0   260    40    45   4.45 0.6153
WVFGRD96   29.0   260    40    45   4.46 0.6115

The best solution is

WVFGRD96   25.0   270    35    55   4.43 0.6201

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.

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 .model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

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 Wed Jul 4 09:40:40 CDT 2018