Location

Location ANSS

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2019/06/01 07:00:28:3 40.50 20.84 10.0 4.8 Albania Stations used: CL.AGRP CL.MALA CL.MG05 CL.PSAM HA.AXAR HA.KALE HA.VILL HL.EVR HL.JAN HL.KZN HL.NEO HL.PENT HL.RDO HL.RLS HL.TETR HL.THL HL.VLS HP.AMPL HP.EFP HP.FSK HP.LTK HP.PVO HT.ALN HT.EVGI HT.HORT HT.IGT HT.KAVA HT.KNT HT.KPRO HT.LKD2 HT.NEST HT.PSDA HT.SOH HT.TYRN HU.KOVH HU.MORH MN.KEK MN.KLV MN.PDG MN.TIR RO.BZS RO.COPA RO.GZR RO.HERR RO.LOT RO.MDVR RO.PUNG 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 = 2.72e+23 dyne-cm Mw = 4.89 Z = 12 km Plane Strike Dip Rake NP1 250 70 30 NP2 149 62 157 Principal Axes: Axis Value Plunge Azimuth T 2.72e+23 35 112 N 0.00e+00 54 281 P -2.72e+23 5 18 Moment Tensor: (dyne-cm) Component Value Mxx -2.20e+23 Mxy -1.42e+23 Mxz -7.04e+22 Myy 1.32e+23 Myz 1.11e+23 Mzz 8.75e+22 ----------- P --------------- ---- ###------------------------- ####-------------------------- ######---------------------------- #######----------------------------- ########------------------------------ ##########--------------################ ##########--------###################### ############--############################ ###########--############################# ########-----############################# ######--------################## ####### ###------------################ T ###### #---------------############### ###### ----------------###################### -----------------################### ------------------################ ------------------############ --------------------######## ---------------------# -------------- Global CMT Convention Moment Tensor: R T P 8.75e+22 -7.04e+22 -1.11e+23 -7.04e+22 -2.20e+23 1.42e+23 -1.11e+23 1.42e+23 1.32e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190601070028/index.html

Preferred Solution

      STK = 250
      DIP = 70
     RAKE = 30
       MW = 4.89
       HS = 12.0

The NDK file is 20190601070028.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGSW

USGS/SLU Moment Tensor Solution ENS 2019/06/01 07:00:28:3 40.50 20.84 10.0 4.8 Albania Stations used: CL.AGRP CL.MALA CL.MG05 CL.PSAM HA.AXAR HA.KALE HA.VILL HL.EVR HL.JAN HL.KZN HL.NEO HL.PENT HL.RDO HL.RLS HL.TETR HL.THL HL.VLS HP.AMPL HP.EFP HP.FSK HP.LTK HP.PVO HT.ALN HT.EVGI HT.HORT HT.IGT HT.KAVA HT.KNT HT.KPRO HT.LKD2 HT.NEST HT.PSDA HT.SOH HT.TYRN HU.KOVH HU.MORH MN.KEK MN.KLV MN.PDG MN.TIR RO.BZS RO.COPA RO.GZR RO.HERR RO.LOT RO.MDVR RO.PUNG 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 = 2.72e+23 dyne-cm Mw = 4.89 Z = 12 km Plane Strike Dip Rake NP1 250 70 30 NP2 149 62 157 Principal Axes: Axis Value Plunge Azimuth T 2.72e+23 35 112 N 0.00e+00 54 281 P -2.72e+23 5 18 Moment Tensor: (dyne-cm) Component Value Mxx -2.20e+23 Mxy -1.42e+23 Mxz -7.04e+22 Myy 1.32e+23 Myz 1.11e+23 Mzz 8.75e+22 ----------- P --------------- ---- ###------------------------- ####-------------------------- ######---------------------------- #######----------------------------- ########------------------------------ ##########--------------################ ##########--------###################### ############--############################ ###########--############################# ########-----############################# ######--------################## ####### ###------------################ T ###### #---------------############### ###### ----------------###################### -----------------################### ------------------################ ------------------############ --------------------######## ---------------------# -------------- Global CMT Convention Moment Tensor: R T P 8.75e+22 -7.04e+22 -1.11e+23 -7.04e+22 -2.20e+23 1.42e+23 -1.11e+23 1.42e+23 1.32e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190601070028/index.html

W-phase Moment Tensor (Mww) Moment 4.404e+16 N-m Magnitude 5.03 Mww Depth 11.5 km Percent DC 91% Half Duration 0.84 s Catalog US Data Source US 1 Contributor US 1 Nodal Planes Plane Strike Dip Rake NP1 34 58 -72 NP2 182 37 -116 Principal Axes Axis Value Plunge Azimuth T 4.295e+16 N-m 11 111 N 0.211e+16 N-m 15 204 P -4.506e+16 N-m 71 347

Magnitudes

mLg Magnitude

(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

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   230    55   -55   4.62 0.4169
WVFGRD96    2.0   225    55   -60   4.73 0.5160
WVFGRD96    3.0   225    60   -60   4.78 0.5269
WVFGRD96    4.0    35    30   -70   4.84 0.5505
WVFGRD96    5.0    30    30   -75   4.86 0.5637
WVFGRD96    6.0   230    60   -50   4.82 0.5614
WVFGRD96    7.0   250    70    30   4.80 0.5688
WVFGRD96    8.0   215    55   -70   4.91 0.5973
WVFGRD96    9.0   250    80    40   4.85 0.5909
WVFGRD96   10.0   250    75    35   4.86 0.5982
WVFGRD96   11.0   250    70    30   4.88 0.6021
WVFGRD96   12.0   250    70    30   4.89 0.6040
WVFGRD96   13.0   250    70    30   4.90 0.6022
WVFGRD96   14.0   250    70    30   4.90 0.5977
WVFGRD96   15.0   250    70    30   4.91 0.5909
WVFGRD96   16.0   250    70    25   4.92 0.5839
WVFGRD96   17.0   250    70    25   4.93 0.5763
WVFGRD96   18.0   250    70    25   4.93 0.5675
WVFGRD96   19.0   250    70    25   4.94 0.5577
WVFGRD96   20.0   250    70    25   4.94 0.5477
WVFGRD96   21.0   250    70    25   4.95 0.5363
WVFGRD96   22.0   250    70    25   4.96 0.5249
WVFGRD96   23.0   250    70    20   4.97 0.5135
WVFGRD96   24.0   250    70    20   4.97 0.5028
WVFGRD96   25.0   250    70    20   4.98 0.4919
WVFGRD96   26.0   250    75    20   4.98 0.4809
WVFGRD96   27.0   250    75    20   4.98 0.4706
WVFGRD96   28.0   250    75    20   4.99 0.4611
WVFGRD96   29.0   250    75    20   5.00 0.4520

The best solution is

WVFGRD96   12.0   250    70    30   4.89 0.6040

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)

 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: