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Titolo: SEISMICWAVE PROPAGATION IN COMPLEX CRUST UPPERMANTLE MEDIA USING 2D FINITEDIFFERENCE SYNTHETICS
Autore: HESTHOLM SO; HUSEBYE ES; RUUD BO;
 Indirizzi:
 IBM CORP,BERGEN ENVIRONM SCI & SOLUT CTR N5008 BERGEN NORWAY UNIV BERGEN,INST SOLID EARTH PHYS N5007 BERGEN NORWAY
 Titolo Testata:
 Geophysical journal international
fascicolo: 3,
volume: 118,
anno: 1994,
pagine: 643  670
 SICI:
 0956540X(1994)118:3<643:SPICCU>2.0.ZU;2R
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 CODA WAVES; MULTIPLESCATTERING; BOUNDARYCONDITIONS; ELASTICWAVES; NORESS ARRAY; LASA; HETEROGENEITY; ATTENUATION; LITHOSPHERE; 3COMPONENT;
 Keywords:
 CODA EXCITATION; 2D FINITE DIFFERENCE; DEFORMATION OF BODYWAVE PHASES; ELASTIC WAVE EQUATION; FREESURFACE TOPOGRAPHY; LITHOSPHERE MODELS; PTORG AND STORG SCATTERING; SYNTHETICS; VON KARMAN RANDOMIZATION;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Science Citation Index Expanded
 Citazioni:
 56
 Recensione:
 Indirizzi per estratti:



 Citazione:
 S.O. Hestholm et al., "SEISMICWAVE PROPAGATION IN COMPLEX CRUST UPPERMANTLE MEDIA USING 2D FINITEDIFFERENCE SYNTHETICS", Geophysical journal international, 118(3), 1994, pp. 643670
Abstract
A description is given of the numerical FD scheme used to solve the elastic wave equation, including a few remarks on the source functions used. Our FD method has been used for computing synthetic seismograms for 2D crust/upper mantle models of size 150 x 400 km(2), with options for freesurface topography. The strategy was to introduce successively more complex lithosphere models for generating the synthetics; thereference model was laterally homogeneous lithosphere. The interface scattering was visualized through displays of freesurface synthetic waveforms and snapshots for models with a corrugated Moho only and freesurface topography only. Near the free surface the latter seems to dominate, in the form of PtoRg and StoRg conversions. Lithosphere randomizations were introduced through von Karman functions of order v =0.3, with rms velocity fluctuations of 34 per cent and correlation distances (horizontal and vertical) at 2.5 or 10 km. In case of a medium with only subMoho heterogeneities, those with horizontal anisotropy(a(x) = 10 km; a(z) = 2.5 km) produced relatively strong Pn and Sn phases. The respective codas were dominated as in most of our experiments by PtoS and StoS scattering wavelets excluding Rg scattering at a free surface with topography. For a medium with crustal heterogeneities, the distortions of the P and S wave trains with distance were clearly demonstrated. For fullscale heterogeneous lithosphere models, characteristic features of the synthetics were quantitatively similar toobservational records of local events. Dominant attributes were a pronounced P coda consisting mainly of P and Rgscattered wavelets, and a relatively strong S coda consisting mainly of PtoS and StoS scattered wavelets. The P and S waveforms are severely distorted pointing at the futility of reliably picking many secondary arrivals in local event recordings. Most of the scattering wavelets are confined to the crustal waveguide and to surface waves, since coda excitations for sensors at a depth of 100 km were weak and, moreover, consisted mainly of S wavelets. This implies that a strong teleseismic P coda does not reflect scattering within the crust in the source region but, rather, a complex source. Observational results from analysis of NORESS and ARCESS local event recordings are also presented. Clearly the lithosphere is not isotropically inhomogeneous. The essence of our 2D FD syntheticseismogram experiments is that a simple lithosphere model, being moderately heterogeneous, gives rise to complex seismograms which are grossly similar to the observational recordings. In contrast, complex models derived from profiling surveys (but lacking the finescale random variations) give simple, 'ray tracing' like synthetics, not necessarilysimilar to the observed records.
ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 01/12/20 alle ore 19:09:46