oceanic lithosphere-3

Solid Earth Geophysics

Ali Onceloncel@kfupm.edu.

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)