TitleOrigin of water layer multiple phases with anomalously high amplitude in near-seafloor wide-angle seismic recordings
Publication TypeJournal Article
Year of Publication2013
AuthorsMeléndez A.a, Sallarès V.a, Ranero C.R.bR, Kormann J.c, Meléndez A., Sallarès V.
JournalGeophysical Journal International
Volume196
Pagination243–252
ISSN0956540X
Keywordsambient noise, Controlled source seismology, Controlled-source seismologies, Earthquake effects, Geometrical spread, hydrophone, Numerical approximations and analysis, numerical method, ocea, Seismology, Site effects, Wave propagation
AbstractWater layer multiple seismic phases are recorded at ocean bottom seismometers and hydrophones as arrivals that correspond to the reflection of the primary phases at the sea-free air interface. In regions of low to moderate seabed relief, the shape of these phases mimics that of the primary phases with a traveltime delay that depends on the water layer thickness at the receiver location. Given their longer travel paths, multiple phases should have smaller amplitudes than their corresponding primary phases. However, depending on the geological context it can be relatively common to observe the opposite, which results in the identification of the multiple phases at longer offsets than the primary events. In this paper, we examine the origin of this apparently paradoxical phenomenon by analysing the combined effect of the major factors potentially involved: the source frequency content, the subsurface velocity distribution, the receiver-seafloor distance, the geometrical spreading and attenuation of sound waves and the ambient noise level.We use synthetic modelling to show that for certain combinations of these factors, the interference between the multiple and its reflection at the seafloor is constructive and has a higher amplitude than the primary wave. Our analysis indicates that in the most favourable cases the phases resulting from this interference can be observed at offsets some tens of kilometres longer than their corresponding primary phases, and thus they can provide useful information for velocity modelling. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.
URLhttp://www.scopus.com/inward/record.url?eid=2-s2.0-84890885715&partnerID=tZOtx3y1 http://www.scopus.com/inward/record.url?eid=2-s2.0-84890885715&partnerID=40&md5=a3729b5c20fafb9373a2a82c94b34990
DOI10.1093/gji/ggt391