We present seismic moment tensor solutions for 63 events at Uturuncu volcano, Bolivia. Moment tensor solutions were generated using body waves and surface waves. The best solution (M0) was obtained through a grid-search in moment tensor space using the "cut-and-paste" (CAP) approach of Zhu and Helmberger (1996) and Zhu and Ben-Zion (2013). The files here are part of the PhD thesis work by Celso AlvizuriThis work was supported by the National Science Foundation (EAR-1215959 and EAR-0909254)

Alvizuri, Celso

English

ScholarWorks@UA

Text Supplement for ScholarWorks@UA collection“Seismic moment tensor catalog for Uturuncu volcano, Bolivia”Celso AlvizuriDecember 7, 2015Attribution: If you use these files, please cite Alvizuri & Tape (2015) and this ScholarWorksentry.Description of filesThe files here are part of the PhD thesis work by Celso Alvizuri. This supplement will be citedin Alvizuri & Tape (2015).A seismic moment tensor catalog of 63 events was generated using first-motion polarities,body waves and surface waves. The best solution (M0) was obtained through a grid-search inthe moment tensor space using the ‘cut-and-paste’ (CAP) approach of Zhu & Helmberger (1996);Zhu & Ben-Zion (2013). Figures are listed in Section 1. The waveform fits for the 63 events inthe catalog are shown in Figure A1. The waveform misfit on the source-type plot for these eventsare shown in Figure B1.A second seismic moment tensor catalog for the same 63 events was generated using bodywaves and surface waves but without first-motion polarities. This second set of figures is listedin Section 1.1 Inversions using first-motion polaritiesFigure A1: Waveform fits (Catalog events) [utuhalf P01 V10 R01 S10 waveform fits.pdf]Waveform fits for 63 moment tensor inversions for which waveform misfit is plotted on the source-type plot. (Figure B). Black are observed waveforms; red are synthetic waveforms computed usinga frequency-wavenumber method (Zhu & Rivera, 2002) that assumes a (1D) layered model. Weuse a homogeneous halfspace model utuhalf. The waveforms are fit separately within five timewindows: P wave vertical component (PV), P wave radial component (PR), Rayleigh wave verticalcomponent (SurfV), Rayleigh wave horizontal component (SurfR), and Love wave transversecomponent (SurfT). At far left in each row is the station name, source-station distance in 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 description of the four header lines:1. Event 20100516063454464 Model and Depth utuhalf_004The event ID is derived from the origin time of 2010-05-16 06:34:54.464.1The halfspace model used is utuhalf, and the event depth is 4 km.2. FM 150 76 -75 Mw 2.80 ISO -10 CLVD 10 rms 1.790e-07 VR 22.1The orientation of the moment tensor solution M0 is strike 150◦, dip 76◦, rake −75◦.The estimated magnitude is Mw 2.8. The ISOtropic coordinate is δ = −10◦ and the CLVDcoordinate is γ = 10◦. The waveform difference between data and synthetics is 1.790×10−7,and the variance reduction is VR = 22.1%.3. Filter periods (seconds): Body:0.10--0.50. Surf:2.00--4.00The body waves were filtered 0.10–0.50 s, the surface waves were filtered 2.00–4.00 s.4. # norm L1 # Pwin 1.5 Swin 60 # N 11 Np 22 Ns 33An L1 norm was used for the misfit function. The (reference) P-window is 1.5 s long, thesurface wave window is 60 s long, there are 11 stations with at least one waveform, 22 isthe number of P windows used, and 33 is the number of surface wave windows used.The numbers below each station are1. source–station epicentral distance, km2. station azimuth, in degrees3. 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)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 windowFigure B1: Summary misfit plots for all 63 events [utuhalf P01 V10 R01 S10 misfit.pdf]Alvizuri & Tape (2015), Figure 6, caption:Full moment tensor misfit summary for the example event. For details, see Section 3. (a) Mapof source location (red star) and stations used in the inversion for this event. The station iscolored blue if the observed first-motion polarity on the vertical component is up (compression)and white if it is down (dilatation). (b) Contour plot of the polarity misfit on the lune. Not to beconfused with the waveform misfit, the polarity misfit n(M) (Eq. 5) for a moment tensorM is thenumber of stations where the observed first-motion polarity differs from the polarity predictedfrom M . The polarity misfit n(Λ) (Eq. 6) at a point Λ on the lune is then the minimum of n(M)for moment tensors M having source type Λ. At each point Λ in the region where n(Λ) = 02(blue), there is therefore a moment tensor M with source type Λ that has correct polarities,that is, polarities that match the observed polarities at all 11 stations. (c) Contour plot ofthe variance reduction VR(Λ). The variance reduction VR(Λ) at a point Λ is the maximumvariance reduction VR(M) for moment tensors M that have source type Λ and that have correctpolarities. (Compare Eq. 7, which is the analog of VR(Λ) for misfit.) Large values (blue) ofVR represent better fit between observed and synthetic waveforms. Since M is required to havecorrect polarities, the plot of VR(Λ) is only defined on the region n(Λ) = 0. The beachballplotted at each point Λ of this region is the moment tensor M(Λ) that maximizes VR(M) withΛ fixed. Of the beachballs M(Λ), our desired solution M0 (green box) is the one with largestVR. The gray arcs on the lune are the great circle arcs λ1 = 0, λ2 = 0, and λ3 = 0 (white, green,and red in Figure 1). Selected eigenvalue triples (black dots) on the boundary of the lune areindicated, with the understanding that the triples need to be normalized. The positive isotropicsource (1, 1, 1) is at the top, the negative isotropic source (−1,−1,−1) is at the bottom, andthe double couple (1, 0,−1), not shown, would be at the center of the lune. (d) The momenttensor M0, the same as in (c) but plotted in a lower-hemisphere projection. For this event, all raypaths travel upward from the source to the stations, so the stations to the east, having upward(compressional) first motions, are plotted on the left of the beachball at the antipode of the raypath direction.Text file table for moment tensor catalog [utuhalf P01 V10 R01 S10 mecha.txt]Seismic moment tensor catalog of 63 events. Details can be found within the header lines, whichalso refer to Kanamori (1977); Silver & Jordan (1982); Tape & Tape (2012).Input text files used in the moment tensor inversion [weights utuhalf P01 V10 R01 S10.zip]We provide a text file for each of the 63 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.2 Inversions without using first-motion polaritiesFigure A2: Waveform fits (Catalog events) [utuhalf P00 V10 R01 S10 waveform fits.pdf]Same as in Figure A1 except polarities are not listed under each station label.Figure B2: Summary misfit plots for all 63 events [utuhalf P00 V10 R01 S10 misfit.pdf]Same as in Figure B1 except that since first-motion polarities are not used, there is no n(Λ)plotted in (b). Beachballs with VR < 0 are considered least likely; we do not plot a beachball atΛ if VR(Λ) < 0.Text file table for moment tensor catalog [utuhalf P00 V10 R01 S10 mecha.txt]Input text files used in the moment tensor inversion [weights utuhalf P00 V10 R01 S10.zip]3ReferencesAlvizuri, C. & Tape, C., 2015. Full moment tensors for small events (Mw < 3) at Uturuncuvolcano, Bolivia, Geophys. J. Int. (in prep.).Kanamori, H., 1977. The energy release in great earthquakes, J. Geophys. Res., 82, 2981–2987.Silver, P. G. & Jordan, T. H., 1982. Optimal estimation of scalar seismic moment, Geophys. J.R. Astron. Soc., 70, 755–787.Tape, W. & Tape, C., 2012. A geometric setting for moment tensors, Geophys. J. Int., 190,476–498, doi:10.1111/j.1365-246X.2012.05491.x.Zhu, L. & Ben-Zion, Y., 2013. Parameterization of general seismic potency and moment tensorsfor source inversion of seismic waveform data, Geophys. J. Int., 194, 839–843, doi:10.1093/gji/ggt137.Zhu, L. & Helmberger, D., 1996. Advancement in source estimation techniques using broadbandregional seismograms, Bull. Seis. Soc. Am., 86(5), 1634–1641.Zhu, L. & Rivera, L. A., 2002. A note on the dynamic and static displacements from a point sourcein multilayered media, Geophys. J. Int., 148, 619–627, doi:10.1046/j.1365-246X.2002.01610.x.4

Seismic moment tensor catalog for Uturuncu volcano, Bolivia

https://scholarworks.alaska.edu/bitstream/11122/6266/9/scholarworks.pdf

Seismic moment tensor catalog for Uturuncu volcano, Bolivia

Abstract

Similar works

Full text

Available Versions

ScholarWorks@UA