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Solid Earth Geophysics
Ali [email protected].
saDepartment of Earth SciencesKFUPM
Today’s class: Oceanic Lithosphere
Reading: Fowler Chapter 9, pp.391-416
Oceanic Crust and Continental Crust
Total Sediment Thickness Database
Depth of Sea Floor versus Age of Sea Floor
Marine Seismic Acquisition
OBS and Streamer
Summary Lecture 12
Chapter Exam
Next Tuesday ClassFowler Chapters 8 and 9, pp.391-416
AssignmentPrepare your questions for Chapter 9n and upload them to class page before the exam.
April 21, 2007
Oman ophiolite
harzburgite
upper mantle
both from: http://www.bris.ac.uk/Depts/Geol/vft/oman.html
Exposed Oceanic Crust
Often regarded as examples of oceanic crust. However, because they are now tectonically emplaced on land, they are atypical and might not represent n normal oceanic crust. Ophiolites are probably samples of young oceanic crust produced in back-arc basins, or fore-arc basins, associated with subduction zones (Fowler, pp.405).
pp. 339 of Stein, 2003 modified after McClousky et al., 2000
Why does the Ocean Depth
with lithospheric age deepens with distance
from the spreading
ridges?
Recall
Depth for OceanAge for Lithosphere
If a body cools, what happens to its density?
MULTICHANNEL
SEISMIC EQUIPMENT
P.Farcy Farcy, B. , B. Marsset Marsset, H. , H. Nouze Nouze
Ocean Bottom Seismograph
http://www.geopro.com/obs.html
The OBS is cased in a glass sphere which can be deployed up to water depths of 6700m, recording seismic signals directly on the seafloor with a gimbal mounted 3C-geophone and a deep sea hydrophone.
http://www.geopro.com/obs.html
V Sea =1525 m/s
Vsediments = 1800 m/s
VMetamorphic =2500 m/s
Reflection signature of seismic and aseismic slip on the northern Cascadia subduction interface, Nedimovic et al.,
NATURE |VOL 424 24 JULY 2003
Nedimovic et al., NATURE |VOL 424 | 24 JULY 2003 |
Wide Aperture Reflection Refraction Profiling
WARPOffshore
The basic principle of WARRP is utilizing the amplitude burst when P-wave energy is totally reflected beyond the critical angle of incidence. To record at wide angles large offsets are required, much larger than conventional seismic arrays can provide.
OBS application with a vertical streamer
http://www.geopro.com
Fig. 1. (a) Tectonic context and general kinematics in the Eastern Mediterranean (from McClusky et al., 2000; Chaumillon et al.,1996; Le Pichon et al., 1995). Main microplate boundaries are shown, as well as the Hellenic trough system and the Mediterranean Ridge outer and inner fronts of deformation. Arrows with numeric values indicate regional motions. (b) Bathymetry map of the Eastern Mediterranean Ridge where the 3-D gravity modelling (rectangle in (a)) was undertaken. Lines show the position of seismic cross-sections in the Crete area (red lines, Bohnhoff et al., 2001) and in the Libyan Sea crossing the Mediterranean Ridge (yellow dashed lines, Makris and Broenner, 2001; Broenner, 2003).
Deep Sea P Sensor
Deep-sea pressure sensors (Germany)
Suggested global distribution of deep sea pressure sensors (to be
defined)
