We determine moment tensor solutions for 53 earthquakes in southern Alaska, which include 9 in Beluga, 22 in Cook Inlet, and 22 in Susitna. The moment tensors were estimated using both the waveforms and the first-motion polarities. The best solution was obtained through a grid-search in the double-couple moment tensor space using the "cut-and-paste" (CAP) approach of Zhu and Helmberger (1996).This project was supported by USGS Earthquake Hazards Program (contract G15AP00052)

Silwal, Vipul

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Text Supplement for ScholarWorks@UA collectionSeismic moment tensor catalog for crustal earthquakes in the Cook Inletand Susitna region of southern AlaskaVipul SilwalVersion 1: May 3, 2018Attribution: If you use these files, please cite Silwal et al. (2018) and Silwal (2018).Description of filesThis collection is established for the submission of a manuscript (Silwal et al., 2018).Three catalogs of seismic moment tensors were generated using first-motion polarities, bodywaves, and surface waves. The best solution (M0) was obtained through a grid-search in themoment tensor space using the ‘cut-and-paste’ (CAP) approach, which allows for different fre-quencies and time shifts on different portions of seismograms (Silwal and Tape, 2016; Zhao andHelmberger , 1994; Zhu and Helmberger , 1996; Zhu and Ben-Zion, 2013). The moment tensorapproach was adapted and applied in Silwal and Tape (2016) for double couple moment tensorsand in Alvizuri and Tape (2016) for full moment tensors. (Silwal et al., 2018) updated the misfitfunction to take into account the polarity error. Alvizuri et al. (2018) applied the updated misfitfunction for estimation of full moment tensors and uncertainty.A summary of files in the collection is listed in the following table:figure description file nameFigure A1 Waveform fits for 9 events around Beluga beluga cap.pdfFigure A2 Waveform fits for 22 events in Cook Inlet basin cookinlet cap.pdfFigure A3 Waveform fits for 22 events in Susitna basin susitna cap.pdfFigure B1 Moment tensor beachballs with input polarity for9 events around Belugabeluga beach cap.pdfFigure B2 Moment tensor beachballs with input polarity for22 events in Cook Inlet basincookinlet beach cap.pdfFigure B3 Moment tensor beachballs with input polarity for22 events in Susitna basinsusitna beach cap.pdf– text file catalog of moment tensors sakmt mech.txt– zipped set of text files of input parameters formoment tensor inversionssakmt weights.zip– this file: summary of collection sakmt scholarworks.pdfWithin each set of figures (A1, A2, A3, B1, B2, B3), the events are in chronological order byorigin time.Figures A1, A2, A3: Waveform fitsWaveform fits for 53 moment tensor inversions in south-central Alaska. Black are observedwaveforms; red are synthetic waveforms computed using a frequency-wavenumber method (Zhuand Rivera, 2002) that assumes a (1D) layered model. The waveforms are fit separately withinfive time windows: P wave vertical component (PV), P wave radial component (PR), Rayleigh1wave vertical component (SurfV), Rayleigh wave horizontal component (SurfR), and Love wavetransverse component (SurfT). At far left in each row is the station name, source-station distancein km, and station azimuth in degrees. Below each pair of waveforms are four numbers: the cross-correlation time shift between data and synthetics, the cross-correlation value, the percent of themisfit function represented by the waveform pair, and the amplitude ratio between waveforms,ln(Aobs/Asyn), where A is the max value of the waveform within the time window.The beachball represents the best solutionM0 (i.e., the global minimum of the misfit function).The beachball is plotted as a lower-hemisphere projection (standard seismological convention) ofthe moment tensor. The surrounding black dots denote the azimuthal location of the stationsused, and the red crosses denote the lower hemisphere piercing points of the ray paths to thestations.Here is a header for an example event in Figure A1: The four header lines are as follows:1. Event 20080126042942584 Model scak Depth 11The event ID is derived from the origin time of 2008-01-26 04:29:42.584.The layered model used is scak, and the event depth is 11 km.2. FM 141 50 67 Mw 3.00 γ 0 δ 0 rms 3.345e-01 VR 88.8 pol_wt 0.30The orientation of the moment tensor solution M0 is strike 141◦, dip 50◦, rake 67◦. Theestimated magnitude is Mw 3.0. The source type of M0 is expressed in terms of lunelongitude γ = 0◦ and lune latitude δ = 0◦. Since we are searching only in double couplespace, γ and δ are zero for all solutions (see (Alvizuri et al., 2018)). The waveform differencebetween data and synthetics is RMS = 3.345e − 01, and the variance reduction is VR =88.8%. These are based on a waveform difference measure that rewards using longer timewindows and broader bandpass limits. This choice means that the VR cannot be directlycompared with VR values reported in other studies. The factor pol_wt = 0.30 determinesthe balance between polarity misfit and waveform misfit (i.e., 0.70 for this example). Avalue of 999.0 means that polarities are not used.3. Filter periods (seconds): Body:0.11-0.25. Surf:12.50-20.00 duration: 0.06/0.03 sThe body waves were filtered 0.11–0.25 s, the surface waves were filtered 12.50–20.00 s. Incases, where no surface wave are used the bandpass range is redundant.The source time function is a trapezoidal function whose duration is 0.06 s and whose risetime is half the duration. The duration is not an estimated source parameter but is setaccording to the target frequency of body waveforms (here 9 Hz).4. # norm L1 # Pwin 1.3 Swin 100 # N 19 Np 37 Ns 0An L1 norm was used for the misfit function (e.g., Silwal and Tape, 2016). The (reference)P-window is 1.3 s long and the surface wave window is 100 s long. Again, these parametersare meaningful only if the body or surface wave components are used for inversion. Froma total of 19 stations (N), 37 P wave windows (Np) and 0 surface wave windows (Ns) wereused. In this example, surface wave bandpass and window length are not used.The numbers below each station are1. source–station epicentral distance, km2. station azimuth, in degrees3. time shift between picked P onset and synthetic P onset.24. sign of the observed first-motion polarity , which is either 1 (up or compression) or −1(down or dilatation). The number in parentheses is the predicted amplitude, which rangesbetween ±√2; numbers close to zero indicate that the station is near a nodal surface of theradiation pattern for the assumed mechanism.The four numbers below each pair of waveforms are1. the cross-correlation time shift ∆T = Tobs − Tsyn required for matching the synthetics s(t)with the data u(t). A positive time-shift means that the synthetics arrive earlier than thedata and that the assumed velocity model is faster than the actual earth structure.2. the maximum cross-correlation percentage between u(t) and s(t−∆T )3. the percentage of the total misfit4. the amplitude ratio ln(Aobs/Asyn) in each time windowFigures B1, B2, B3: Beachballs with polaritiesHere is a header for an example event in Figure B1:The two header lines are as follows:1. Event 20080126042942584 Model 20080126042942584_scak_011Same as the header line 1 for waveform fits plot.2. FM 141 50 67 Mw 3.00 γ 0 δ 0 rms 3.345e-01 VR 88.8 pol_wt 0.30Same as the header line 2 for waveform fits plot.The dot (·) at the station name outside mark the azimuthal location. The lower hemispherepiercing points are marked with cross (x). The upper hemisphere piercing points are markedwith circle (o). For these stations, lower hemisphere piercing point is also marked in (x).Triangle is marked instead of (x) for stations with observed polarity specified in the weightfile. The observed up polarity (compression) is marked with upward pointing triangle,whereas, the down polarity (dilation) is marked with downward pointing triangle. Thetriangles are colored green if observed and theoretical polarity matches for compressionalquadrant, and, blue if observed and theoretical polarity matches for dialational quadrant.This makes it easier to visualize. The triangles are colored red if the observed polarity doesnot matches with the theoretical polarity of the moment tensor beachball.Text file tables for moment tensor catalogs [sakmt mech.txt]Seismic moment tensor catalogs. Details can be found within the header lines, which also referto Kanamori (1977); Aki and Richards (1980); Silver and Jordan (1982); Minson et al. (2007);Tape and Tape (2012, 2013, 2015).Input text files used in the moment tensor inversion [sakmt weights.zip]We provide a text file for each of the 53 events in this study. These files show which stationsand which time windows were used (or not) in each moment tensor inversion. It also shows thefirst-motion polarity observations that were used.3ReferencesAki, K., and P. G. Richards (1980), Quantitative Seismology, Theory and Methods, W. H. Free-man, San Francisco, Calif., USA.Alvizuri, C., and C. Tape (2016), Full moment tensors for small events (Mw < 3) at Uturuncuvolcano, Bolivia, Geophys. J. Int., 206, 1761–1783, doi:10.1093/gji/ggw247.Alvizuri, C., V. Silwal, L. Krischer, and C. Tape (2018), Estimation of full moment tensors, in-cluding uncertainties, for nuclear explosions, volcanic events, and earthquakes, J. Geophys. Res.Solid Earth (in press), doi:10.1029/2017JB015325.Kanamori, H. (1977), The energy release in great earthquakes, J. Geophys. Res., 82, 2981–2987.Minson, S. E., D. S. Dreger, R. Bu¨rgmann, H. Kanamori, and K. M. Larson (2007), Seismicallyand geodetically determined nondouble-couple source mechanisms from the 2000 Miyakejimavolcanic earthquake swarm, J. Geophys. Res., 112, B10308, doi:10.1029/2006JB004847.Silver, P. G., and T. H. Jordan (1982), Optimal estimation of scalar seismic moment, Geophys. J.R. Astron. Soc., 70, 755–787.Silwal, V. (2018), Seismic moment tensor catalog for crustal earthquakes in the Cook Inlet andSusitna region of southern Alaska, ScholarWorks@UA: descriptor file, text file of catalog, figureswith waveform fits, and input weight files.Silwal, V., and C. Tape (2016), Seismic moment tensors and estimated uncertainties in southernAlaska, J. Geophys. Res. Solid Earth, 121, 2772–2797, doi:10.1002/2015JB012588.Silwal, V., C. Tape, and A. Lomax (2018), Crustal earthquakes in the Cook Inlet and Susitnaregion of southern Alaska, Tectonophysics (in prep).Tape, W., and C. Tape (2012), A geometric setting for moment tensors, Geophys. J. Int., 190,476–498, doi:10.1111/j.1365-246X.2012.05491.x.Tape, W., and C. Tape (2013), The classical model for moment tensors, Geophys. J. Int., 195,1701–1720, doi:10.1093/gji/ggt302.Tape, W., and C. Tape (2015), A uniform parameterization of moment tensors, Geophys. J. Int.,202, 2074–2081, doi:10.1093/gji/ggv262.Zhao, L.-S., and D. V. Helmberger (1994), Source estimation from broadband regional seismo-grams, Bull. Seismol. Soc. Am., 84 (1), 91–104.Zhu, L., and Y. Ben-Zion (2013), Parameterization of general seismic potency and momenttensors for source inversion of seismic waveform data, Geophys. J. Int., 194, 839–843, doi:10.1093/gji/ggt137.Zhu, L., and D. Helmberger (1996), Advancement in source estimation techniques using broad-band regional seismograms, Bull. Seismol. Soc. Am., 86 (5), 1634–1641.Zhu, L., and L. A. Rivera (2002), A note on the dynamic and static displacements from a pointsource in multilayered media, Geophys. J. Int., 148, 619–627, doi:10.1046/j.1365-246X.2002.01610.x.41 secs. 60 secs.YV.NANC..BH65 km76° 0.7 s−1 (−0.98)YV.KASH..BH69 km60° 0.8 s−1 (−0.98)AK.FIB..BH71 km127° 2.1 s−1 (−0.18)YV.BIGB..BH75 km86° 1.6 s−1 (−0.89)YV.CASW..BH79 km50° 1.0 s−1 (−0.21)YV.KNIK..BH83 km94° 1.9 s−1 (−0.33)YV.COOK..BH85 km172° 2.5 sYV.MCDC..BH93 km104° 1.1 sAK.RC01..BH95 km122° 1.1 s−1 (−0.10)YV.ALPI..BH96 km110° 1.1 sYV.MPEN..BH100 km181° 2.5 sAT.PMR..BH111 km156° 1.1 s−1 (−0.37)YV.INDI..BH111 km87° 1.5 s−1 (−0.10)YV.HOPE..BH116 km123° 1.5 sYV.BING..BH119 km130° 2.4 s1 (0.08)YV.LSKI..BH127 km166° 2.1 s1 (0.10)YV.HOPJ..BH130 km176° 2.0 s1 (0.02)YV.USKI..BH134 km160° 1.5 s1 (0.10)YV.BYR..BH136 km131° 1.8 s1 (0.30)YV.LSUM..BH136 km154° 2.0 sYV.TUPA..BH138 km150° 2.1 s−1 (−0.02)YV.DEVL..BH143 km22° 1.7 s0.83903.400.07P V P R0.66726.750.980.66744.60−1.122.16744.591.852.16730.98−0.891.70719.841.411.70566.470.640.91753.280.860.9103.21−0.232.15812.000.442.15362.42−2.092.64651.202.832.64370.170.561.11831.921.101.1102.660.041.27773.531.921.27651.340.861.17623.741.491.17614.931.542.45631.171.032.45510.650.161.15432.04−0.081.15472.10−0.751.43472.281.601.43542.321.421.45561.581.821.45831.021.492.45932.162.012.45210.820.722.04881.090.432.04860.730.102.09924.483.092.09883.792.962.38702.282.662.38772.572.711.71741.061.571.71520.831.17Surf V Surf R Surf TEvent 20080126042942584 Model scak Depth 11FM 141 50 67 Mw 3.00 γ   0 δ   0 rms 3.345e−01 VR 88.8 pol_wt 0.30 Filter periods (seconds): Body:0.11−0.25. Surf:12.50−20.00 duration: 0.06/0.03 s# norm L1    # Pwin 1.3 Swin 100    # N 19 Np 37 Ns 0Figure A1-1: Example from p. 1 of the set of 9 events in Figure A1.5YV.NANC.YV.KASH.AK.FIB.YV.BIGB.YV.CASW.YV.KNIK.YV.COOK.YV.MCDC.AK.RC01.YV.ALPI.YV.MPEN.AT.PMR.YV.INDI.YV.HOPE.YV.BING.YV.LSKI.YV.HOPJ.YV.USKI.YV.BYR.YV.LSUM.YV.TUPA.YV.DEVL.YV.NANC.YV.KASH.AK.FIB.YV.BIGB.YV.CASW.YV.KNIK.YV.COOK.YV.MCDC.AK.RC01.YV.ALPI.YV.MPEN.AT.PMR.YV.INDI.YV.HOPE.YV.BING.YV.LSKI.. J.YV.USKI.YV.BYR.YV.LSUM.YV.TUPA.YV.DEVL.Event 20080126042942584 Model 20080126042942584_scak_011FM 141 50 67 Mw 3.00 γ   0 δ   0 rms 3.345e−01 VR 88.8 pol_wt 0.30Figure B1-1: Example from p. 1 of the set of 9 events in Figure B1.6

Seismic moment tensor catalog for crustal earthquakes in the Cook Inlet and Susitna region of southern Alaska

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Seismic moment tensor catalog for crustal earthquakes in the Cook Inlet and Susitna region of southern Alaska

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