The ANSS event ID is ak2025zcuptx and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak2025zcuptx/executive.
2025/12/22 14:59:48 60.528 -140.023 5.0 4.6 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2025/12/22 14:59:48.0 60.53 -140.02 5.0 4.6 Yukon, Canada
Stations used:
AK.BAGL AK.BERG AK.BESE AK.CCB AK.CRQ AK.CYK AK.DIV AK.DOT
AK.EYAK AK.GRES AK.GRIN AK.GRNC AK.HDA AK.HIN AK.ISLE
AK.J25K AK.K24K AK.KHIT AK.KIAG AK.LOGN AK.M23K AK.M26K
AK.MCAR AK.MDM AK.MESA AK.NEA2 AK.PIN AK.PNL AK.POKR AK.PPD
AK.PS08 AK.PWL AK.RAG AK.RC01 AK.RIDG AK.RKAV AK.S31K
AK.SCM AK.SCRK AK.SWD AK.TGL AK.U33K AK.WAT6 AK.WRH AT.SIT
CN.BRWY CN.BVCY CN.PLBC CN.WHY IU.COLA PQ.KLONY US.WRAK
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.12 n 3
Best Fitting Double Couple
Mo = 6.84e+22 dyne-cm
Mw = 4.49
Z = 12 km
Plane Strike Dip Rake
NP1 160 76 159
NP2 255 70 15
Principal Axes:
Axis Value Plunge Azimuth
T 6.84e+22 24 116
N 0.00e+00 65 307
P -6.84e+22 4 208
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.17e+22
Mxy -5.09e+22
Mxz -7.25e+21
Myy 3.03e+22
Myz 2.53e+22
Mzz 1.14e+22
--------------
####------------------
#######---------------------
########----------------------
##########------------------------
###########-------------------------
#############-------------------------
##############-------------#########----
###############---######################
#############---##########################
#########--------#########################
######------------########################
####--------------########################
#-----------------############### ####
-------------------############## T ####
-------------------############# ###
-------------------#################
-------------------###############
------------------############
--- ------------##########
P -------------######
--------------
Global CMT Convention Moment Tensor:
R T P
1.14e+22 -7.25e+21 -2.53e+22
-7.25e+21 -4.17e+22 5.09e+22
-2.53e+22 5.09e+22 3.03e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20251222145948/index.html
|
STK = 255
DIP = 70
RAKE = 15
MW = 4.49
HS = 12.0
The NDK file is 20251222145948.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
 |
The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) the waveform inversion are shown in the next figure.
|
|
|
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's 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.12 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 65 70 -30 4.28 0.3721
WVFGRD96 2.0 60 60 -35 4.36 0.4157
WVFGRD96 3.0 255 65 10 4.35 0.4164
WVFGRD96 4.0 255 65 10 4.36 0.4347
WVFGRD96 5.0 255 65 10 4.37 0.4522
WVFGRD96 6.0 255 70 15 4.39 0.4795
WVFGRD96 7.0 255 70 15 4.41 0.4999
WVFGRD96 8.0 255 70 15 4.42 0.5160
WVFGRD96 9.0 255 70 15 4.44 0.5288
WVFGRD96 10.0 255 70 15 4.46 0.5416
WVFGRD96 11.0 255 70 15 4.48 0.5478
WVFGRD96 12.0 255 70 15 4.49 0.5507
WVFGRD96 13.0 255 70 15 4.50 0.5505
WVFGRD96 14.0 255 70 15 4.51 0.5481
WVFGRD96 15.0 255 65 15 4.52 0.5444
WVFGRD96 16.0 255 65 10 4.52 0.5409
WVFGRD96 17.0 255 65 10 4.53 0.5362
WVFGRD96 18.0 255 65 10 4.54 0.5301
WVFGRD96 19.0 255 65 10 4.55 0.5235
WVFGRD96 20.0 255 60 15 4.57 0.5189
WVFGRD96 21.0 255 60 15 4.58 0.5109
WVFGRD96 22.0 255 60 10 4.58 0.5026
WVFGRD96 23.0 255 60 10 4.59 0.4942
WVFGRD96 24.0 255 60 10 4.59 0.4857
WVFGRD96 25.0 255 60 10 4.59 0.4769
WVFGRD96 26.0 255 60 10 4.60 0.4679
WVFGRD96 27.0 255 60 10 4.60 0.4584
WVFGRD96 28.0 255 60 10 4.61 0.4494
WVFGRD96 29.0 255 60 10 4.61 0.4414
The best solution is
WVFGRD96 12.0 255 70 15 4.49 0.5507
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.12 n 3
|
| Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
|
| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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:
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.
The CUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
MODEL.01 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00