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Titolo:
SEISMIC-WAVE PROPAGATION IN COMPLEX CRUST UPPER-MANTLE MEDIA USING 2-D FINITE-DIFFERENCE SYNTHETICS
Autore:
HESTHOLM SO; HUSEBYE ES; RUUD BO;
Indirizzi:
IBM CORP,BERGEN ENVIRONM SCI & SOLUT CTR N-5008 BERGEN NORWAY UNIV BERGEN,INST SOLID EARTH PHYS N-5007 BERGEN NORWAY
Titolo Testata:
Geophysical journal international
fascicolo: 3, volume: 118, anno: 1994,
pagine: 643 - 670
SICI:
0956-540X(1994)118:3<643:SPICCU>2.0.ZU;2-R
Fonte:
ISI
Lingua:
ENG
Soggetto:
CODA WAVES; MULTIPLE-SCATTERING; BOUNDARY-CONDITIONS; ELASTIC-WAVES; NORESS ARRAY; LASA; HETEROGENEITY; ATTENUATION; LITHOSPHERE; 3-COMPONENT;
Keywords:
CODA EXCITATION; 2-D FINITE DIFFERENCE; DEFORMATION OF BODY-WAVE PHASES; ELASTIC WAVE EQUATION; FREE-SURFACE TOPOGRAPHY; LITHOSPHERE MODELS; P-TO-RG AND S-TO-RG 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., "SEISMIC-WAVE PROPAGATION IN COMPLEX CRUST UPPER-MANTLE MEDIA USING 2-D FINITE-DIFFERENCE SYNTHETICS", Geophysical journal international, 118(3), 1994, pp. 643-670

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 2-D crust/upper mantle models of size 150 x 400 km(2), with options for free-surface 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 free-surface 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 P-to-Rg and S-to-Rg conversions. Lithosphere randomizations were introduced through von Karman functions of order v =0.3, with rms velocity fluctuations of 3-4 per cent and correlation distances (horizontal and vertical) at 2.5 or 10 km. In case of a medium with only sub-Moho 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 P-to-S and S-to-S 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 full-scale 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 Rg-scattered wavelets, and a relatively strong S coda consisting mainly of P-to-S and S-to-S 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 2-D 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 fine-scale 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