The role of topography and lateral velocity heterogeneities on near-source scattering and ground-motion variability

Handle URI:
http://hdl.handle.net/10754/577020
Title:
The role of topography and lateral velocity heterogeneities on near-source scattering and ground-motion variability
Authors:
Imperatori, W.; Mai, Paul Martin ( 0000-0002-9744-4964 )
Abstract:
The scattering of seismic waves travelling in the Earth is not only caused by random velocity heterogeneity but also by surface topography. Both factors are known to strongly affect ground-motion complexity even at relatively short distance from the source. In this study, we simulate ground motion with a 3-D finite-difference wave propagation solver in the 0–5 Hz frequency band using three topography models representative of the Swiss alpine region and realistic heterogeneous media characterized by the Von Karman correlation functions. Subsequently, we analyse and quantify the characteristics of the scattered wavefield in the near-source region. Our study shows that both topography and velocity heterogeneity scattering may excite large coda waves of comparable relative amplitude, especially at around 1 Hz, although large variability in space may occur. Using the single scattering model, we estimate average QC values in the range 20–30 at 1 Hz, 36–54 at 1.5 Hz and 62–109 at 3 Hz for constant background velocity models with no intrinsic attenuation. In principle, envelopes of topography-scattered seismic waves can be qualitatively predicted by theoretical back-scattering models, while forward- or hybrid-scattering models better reproduce the effects of random velocity heterogeneity on the wavefield. This is because continuous multiple scattering caused by small-scale velocity perturbations leads to more gentle coda decay and envelope broadening, while topography abruptly scatters the wavefield once it impinges the free surface. The large impedance contrast also results in more efficient mode mixing. However, the introduction of realistic low-velocity layers near the free surface increases the complexity of ground motion dramatically and indicates that the role of topography in elastic waves scattering can be relevant especially in proximity of the source. Long-period surface waves can form most of the late coda, especially when intrinsic attenuation is taken into account. Our simulations indicate that both topography and velocity heterogeneity scattering may result in large ground-motion variability, characterized by standard deviation values in the range 0.2–0.5 also at short distance from the source. We conclude that both topography and velocity heterogeneity should be considered to correctly assess the ground-motion variability in earthquake scenario studies even at intermediate frequency.
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Citation:
The role of topography and lateral velocity heterogeneities on near-source scattering and ground-motion variability 2015, 202 (3):2163 Geophysical Journal International
Publisher:
Oxford University Press (OUP)
Journal:
Geophysical Journal International
Issue Date:
28-Jul-2015
DOI:
10.1093/gji/ggv281
Type:
Article
ISSN:
0956-540X; 1365-246X
Additional Links:
http://gji.oxfordjournals.org/lookup/doi/10.1093/gji/ggv281
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division

Full metadata record

DC FieldValue Language
dc.contributor.authorImperatori, W.en
dc.contributor.authorMai, Paul Martinen
dc.date.accessioned2015-09-09T13:56:26Zen
dc.date.available2015-09-09T13:56:26Zen
dc.date.issued2015-07-28en
dc.identifier.citationThe role of topography and lateral velocity heterogeneities on near-source scattering and ground-motion variability 2015, 202 (3):2163 Geophysical Journal Internationalen
dc.identifier.issn0956-540Xen
dc.identifier.issn1365-246Xen
dc.identifier.doi10.1093/gji/ggv281en
dc.identifier.urihttp://hdl.handle.net/10754/577020en
dc.description.abstractThe scattering of seismic waves travelling in the Earth is not only caused by random velocity heterogeneity but also by surface topography. Both factors are known to strongly affect ground-motion complexity even at relatively short distance from the source. In this study, we simulate ground motion with a 3-D finite-difference wave propagation solver in the 0–5 Hz frequency band using three topography models representative of the Swiss alpine region and realistic heterogeneous media characterized by the Von Karman correlation functions. Subsequently, we analyse and quantify the characteristics of the scattered wavefield in the near-source region. Our study shows that both topography and velocity heterogeneity scattering may excite large coda waves of comparable relative amplitude, especially at around 1 Hz, although large variability in space may occur. Using the single scattering model, we estimate average QC values in the range 20–30 at 1 Hz, 36–54 at 1.5 Hz and 62–109 at 3 Hz for constant background velocity models with no intrinsic attenuation. In principle, envelopes of topography-scattered seismic waves can be qualitatively predicted by theoretical back-scattering models, while forward- or hybrid-scattering models better reproduce the effects of random velocity heterogeneity on the wavefield. This is because continuous multiple scattering caused by small-scale velocity perturbations leads to more gentle coda decay and envelope broadening, while topography abruptly scatters the wavefield once it impinges the free surface. The large impedance contrast also results in more efficient mode mixing. However, the introduction of realistic low-velocity layers near the free surface increases the complexity of ground motion dramatically and indicates that the role of topography in elastic waves scattering can be relevant especially in proximity of the source. Long-period surface waves can form most of the late coda, especially when intrinsic attenuation is taken into account. Our simulations indicate that both topography and velocity heterogeneity scattering may result in large ground-motion variability, characterized by standard deviation values in the range 0.2–0.5 also at short distance from the source. We conclude that both topography and velocity heterogeneity should be considered to correctly assess the ground-motion variability in earthquake scenario studies even at intermediate frequency.en
dc.language.isoenen
dc.publisherOxford University Press (OUP)en
dc.relation.urlhttp://gji.oxfordjournals.org/lookup/doi/10.1093/gji/ggv281en
dc.rightsArchived with thanks to Geophysical Journal Internationalen
dc.subjectEarthquake ground motionsen
dc.subjectComputational seismologyen
dc.subjectwave propagationen
dc.titleThe role of topography and lateral velocity heterogeneities on near-source scattering and ground-motion variabilityen
dc.typeArticleen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.identifier.journalGeophysical Journal Internationalen
dc.eprint.versionPublisher's Version/PDFen
dc.contributor.institutionSwiss Seismological Service, Eidgenössische Technische Hochschule (ETH) Zürich, Sonneggstrasse 5, CH-8092 Zurich, Switzerland.en
dc.contributor.affiliationKing Abdullah University of Science and Technology (KAUST)en
kaust.authorMai, Paul Martinen
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