Deconvolving orbital surface waves for the source duration of large earthquakes and modeling the receiver functions for the earth structure beneath a broadband seismometer array in the Cascadia subduction zone

Posted on:1998-09-29

Degree:Ph.D

Type:Thesis

University:Oregon State University

Candidate:Li, Xiao-Qing

Full Text:PDF

GTID:2460390014474491

Subject:Geophysics

Abstract/Summary:

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Four studies comprise this thesis. In the first study, we present a technique to deconvolve orbital surface waves for the source time-delay spectra of large earthquakes. Using auto-correlation and self-convolution functions derived from whole seismograms of large earthquakes, it is possible to isolate the source effects and precisely ({dollar}{bsol}pm{dollar}5 s) determine the source time-delay spectrum at periods as long as 600 s. We apply this technique to five large earthquakes and the results are consistent with those obtained by other researchers.; In the second study, we analyze the receiver functions from a broadband seismic station (COR) in Corvallis, Oregon, for the geometry of subducting Juan de Fuca (JdF) plate. Modeling indicates that the JdF Moho beneath COR is at 40 km depth, dipping 10{dollar}{bsol}sp{bsol}circ{dollar} eastward, and the average Poisson's ratio of the overlying crust is high (0.33). The oceanic crust of JdF plate is modeled as a {dollar}{bsol}sim{dollar}6 km thick low-velocity layer above the Moho.; In the third study, the receiver functions from a linear broadband seismometer array are used. The array is about 15 km south of COR, extending 300 km from the coast to Central Oregon. Modeling indicates that the JdF Moho can be traced from 30{dollar}{bsol}pm{dollar}1 km depth beneath the coast to {dollar}{bsol}sim{dollar}76 km depth beneath the Western/High Cascades ({dollar}{bsol}sim{dollar}145 km from the coast). The dip of the JdF plate is 11{dollar}{bsol}sp{bsol}circ{dollar} under the Coast Range, increasing to 23{dollar}{bsol}sp{bsol}circ{dollar} at 43 km depth under the Willamette Valley. The North America (NA) Moho is at 34-35 km depth beneath Central Oregon. The average Poisson's ratios are 0.33{dollar}{bsol}pm{dollar}0.02 for the crust beneath the Coast Range; 0.28{dollar}{bsol}pm{dollar}0.01 for the NA crust; and 0.25 for the NA mantle wedge.; In the fourth study, we present a technique to perform single-trace deconvolution of seismic array data. The technique is based on spiking deconvolution and utilizes array data processing methods (stacking). Using this technique, we deconvolve teleseismic vertical P and transverse S waves to extract the near-receiver structural information on these two components.

Keywords/Search Tags:

Waves, Large earthquakes, Receiver functions, Technique, Beneath, Array, Source, Modeling

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