[SIO GP Seminars] Geophysics seminar in 15 mins

[Karen Weitemeyer]

In 15 mins.



> Join us today, Friday May 5th, for Geophysics Seminar series.
>
> ========================
>
> Friday, May 5, 3:00 PM
> (refreshments served at 2:45 PM)
> Munk Conference Room
>
> Mladen Nedimovic
> Lamont-Doherty Earth Observatory
>
>  Structure and evolution of the oceanic Juan de Fuca plate from  
> accretion to subduction
>
> =====================
>
> ABSTRACT
> The region comprising the northeast Pacific Ocean and the Cascadia  
> margin is a natural laboratory for studies of various tectonic and  
> geologic processes of global importance. Seafloor spreading, slab  
> bending and hydration, oceanic subduction and interplate coupling,  
> and slab dehydration and intraslab seismicity are some of the many  
> processes that occur within a distance of only several hundred  
> kilometers. I will first briefly describe the study area, the  
> general crustal structure, and the operating tectonic and geologic  
> processes. Then, I will focus on presenting and interpreting three  
> specific observations that can be made by analyzing seismic  
> reflection images. In the direction of increasing crustal age these  
> are: Reflections from localized thick Moho transition zones, normal  
> faulting seaward from the trench, and variable megathrust  
> reflectivity. Imaged thick Moho transition zones appear to provide  
> support for the existence of complex magmatic plumbing systems at  
> mid-ocean ridges and for the crustal generation hypothesis from  
> multiple magma bodies. Extensional regimes seaward of subduction  
> trenches and due to slab bending are likely the key for hydrating  
> the approaching oceanic slabs but at the Cascadia margin this  
> process appears to be mostly limited to the crust, possibly  
> resulting in reduced occurrence rate and magnitude of intraslab  
> seismicity. Variations in the character and thickness of the  
> megathrust reflection package seem to provide a high-resolution  
> method for mapping at least the landward end of maximum co-seismic  
> slip during subduction earthquakes.
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