Location

Location ANSS

2018/07/04 09:01:08 41.49 19.53 10.0 4.9 Albania

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2018/07/04 09:01:08:7 41.49 19.53 10.0 4.9 Albania Stations used: BS.ELND CL.AGRP CL.MALA CL.MG05 CL.ROD3 CL.TRIZ HA.AXAR HA.KALE HA.LOUT HA.MAKR HA.VILL HL.EVR HL.JAN HL.KLV HL.KYMI HL.LIA HL.LKR HL.NEO HL.NVR HL.PENT HL.PLG HL.RDO HL.RLS HL.SKY HL.SMTH HL.VLS HP.AMT HP.ANX HP.GUR HP.LTHK HT.AGG HT.ALN HT.EVGI HT.FNA HT.HORT HT.IGT HT.KAVA HT.KOKK HT.KPRO HT.LKD2 HT.LRSO HT.NEST HT.NYDR HT.OUR HT.PSDA HT.SOH HT.SRS HT.THAS HT.THE HU.KOVH HU.MORH ME.KOME MN.BZS MN.PDG RO.BAIL RO.BANR RO.COPA RO.DEV RO.GZR RO.HERR RO.HUMR RO.LOT RO.MDVR RO.SIRR RO.VLAD SJ.BBLS SJ.FRGS Filtering commands used: cut o DIST/3.3 -20 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 = 6.03e+23 dyne-cm Mw = 5.12 Z = 25 km Plane Strike Dip Rake NP1 155 75 90 NP2 335 15 90 Principal Axes: Axis Value Plunge Azimuth T 6.03e+23 60 65 N 0.00e+00 -0 155 P -6.03e+23 30 245 Moment Tensor: (dyne-cm) Component Value Mxx -5.38e+22 Mxy -1.15e+23 Mxz 2.21e+23 Myy -2.47e+23 Myz 4.73e+23 Mzz 3.01e+23 -#######------ --###############----- -----###################---- -------####################--- ---------#####################---- ----------#######################--- ------------#######################--- -------------########################--- --------------########### #########--- ----------------########## T ##########--- ----------------########## ##########--- -----------------######################--- ------------------#####################--- ----- ----------####################-- ----- P -----------###################-- ---- ------------#################-- -------------------###############-- --------------------############-- -------------------##########- -------------------########- ------------------#### -------------- Global CMT Convention Moment Tensor: R T P 3.01e+23 2.21e+23 -4.73e+23 2.21e+23 -5.38e+22 1.15e+23 -4.73e+23 1.15e+23 -2.47e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180704090108/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 = 155
      DIP = 75
     RAKE = 90
       MW = 5.12
       HS = 25.0

The NDK file is 20180704090108.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 09:01:08:7 41.49 19.53 10.0 4.9 Albania Stations used: BS.ELND CL.AGRP CL.MALA CL.MG05 CL.ROD3 CL.TRIZ HA.AXAR HA.KALE HA.LOUT HA.MAKR HA.VILL HL.EVR HL.JAN HL.KLV HL.KYMI HL.LIA HL.LKR HL.NEO HL.NVR HL.PENT HL.PLG HL.RDO HL.RLS HL.SKY HL.SMTH HL.VLS HP.AMT HP.ANX HP.GUR HP.LTHK HT.AGG HT.ALN HT.EVGI HT.FNA HT.HORT HT.IGT HT.KAVA HT.KOKK HT.KPRO HT.LKD2 HT.LRSO HT.NEST HT.NYDR HT.OUR HT.PSDA HT.SOH HT.SRS HT.THAS HT.THE HU.KOVH HU.MORH ME.KOME MN.BZS MN.PDG RO.BAIL RO.BANR RO.COPA RO.DEV RO.GZR RO.HERR RO.HUMR RO.LOT RO.MDVR RO.SIRR RO.VLAD SJ.BBLS SJ.FRGS Filtering commands used: cut o DIST/3.3 -20 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 = 6.03e+23 dyne-cm Mw = 5.12 Z = 25 km Plane Strike Dip Rake NP1 155 75 90 NP2 335 15 90 Principal Axes: Axis Value Plunge Azimuth T 6.03e+23 60 65 N 0.00e+00 -0 155 P -6.03e+23 30 245 Moment Tensor: (dyne-cm) Component Value Mxx -5.38e+22 Mxy -1.15e+23 Mxz 2.21e+23 Myy -2.47e+23 Myz 4.73e+23 Mzz 3.01e+23 -#######------ --###############----- -----###################---- -------####################--- ---------#####################---- ----------#######################--- ------------#######################--- -------------########################--- --------------########### #########--- ----------------########## T ##########--- ----------------########## ##########--- -----------------######################--- ------------------#####################--- ----- ----------####################-- ----- P -----------###################-- ---- ------------#################-- -------------------###############-- --------------------############-- -------------------##########- -------------------########- ------------------#### -------------- Global CMT Convention Moment Tensor: R T P 3.01e+23 2.21e+23 -4.73e+23 2.21e+23 -5.38e+22 1.15e+23 -4.73e+23 1.15e+23 -2.47e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180704090108/index.html

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 -20 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   170    45   -90   4.74 0.2440
WVFGRD96    2.0   170    45   -90   4.83 0.2917
WVFGRD96    3.0   170    45   -90   4.86 0.2635
WVFGRD96    4.0   295    55   -35   4.76 0.2291
WVFGRD96    5.0   295    55   -30   4.78 0.2340
WVFGRD96    6.0   295    60   -25   4.79 0.2393
WVFGRD96    7.0   155    80    85   4.88 0.2644
WVFGRD96    8.0   155    80    85   4.96 0.2869
WVFGRD96    9.0   155    80    85   4.97 0.3202
WVFGRD96   10.0   155    75    85   4.99 0.3488
WVFGRD96   11.0   155    75    85   5.00 0.3755
WVFGRD96   12.0   350    15   105   5.00 0.3983
WVFGRD96   13.0   155    75    85   5.01 0.4183
WVFGRD96   14.0   155    75    85   5.02 0.4354
WVFGRD96   15.0   155    70    85   5.03 0.4509
WVFGRD96   16.0   155    70    85   5.04 0.4643
WVFGRD96   17.0   155    70    85   5.05 0.4756
WVFGRD96   18.0   155    70    85   5.05 0.4850
WVFGRD96   19.0   155    70    85   5.06 0.4926
WVFGRD96   20.0   155    70    85   5.07 0.4987
WVFGRD96   21.0   155    70    85   5.08 0.5042
WVFGRD96   22.0   155    70    85   5.09 0.5074
WVFGRD96   23.0   155    70    85   5.10 0.5095
WVFGRD96   24.0   155    75    90   5.11 0.5112
WVFGRD96   25.0   155    75    90   5.12 0.5121
WVFGRD96   26.0   155    75    90   5.12 0.5119
WVFGRD96   27.0   155    75    90   5.13 0.5108
WVFGRD96   28.0   150    75    85   5.14 0.5088
WVFGRD96   29.0   150    75    85   5.14 0.5059

The best solution is

WVFGRD96   25.0   155    75    90   5.12 0.5121

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 -20 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:

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 Wed Jul 4 12:48:38 CDT 2018