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  PI-LAB  -  2016  -  Marcus Langseth  
  Project Information  
Project Title: Passive Imaging of the Lithosphere-Asthenosphere Boundary Project Status: Submitted
Principal Investigator: Catherine A. Rychert, UoS Project Institution: UoS
Project ID: 104909 Version #: 3
Date Submitted: 7/16/2015 7:17:00 AM Created By: Catherine A. Rychert
Date Last Modified: 7/28/2015 4:33:00 PM URI Serial #: None
Funding Agencies: OTHER - NE/M003507/1 - Funded
Summary of Field Work: Plate Tectonics is the foundation of modern earth sciences, and provides basic framework for the origin of continents, ocean basins and mountain ranges. Plate Tectonics describe the division of the surface area of the earth into several plates that move independently over the surface of the planet. Each plate acts as an essentially rigid solid shell, which is called Lithosphere, and floats over the material below that flows slowly, called Asthenosphere (Figure 1). Most of the geological activities occur at plate boundaries as the solid lithosphere moves independently, producing giant earthquakes such as 2004 Sumatra and 2011 Japan, volcanoes, great mountains such as the Himalayas, the Andes.
The base of the lithosphere, Lithosphere Asthenosphere Boundary (LAB), is the lower boundary of the plate. There are many definitions of the LAB, depending upon the method used. In one model, the LAB is defined as an isotherm (a surface of constant temperature), which is ~1300? C, melting point of mantle rocks. The rocks above this isotherm are sufficiently cool to behave rigidly, whereas rocks lying below this isotherm are sufficiently hot so they deform readily and flow. Beneath the oceans under this model, the base of this isotherm, and hence LAB, is controlled by cooling of the lithosphere as it moves away from spreading centres where it could be 2-6 km thick at zero age and thicken to ~100 km by the time it reaches 120 Ma toward continents or subduction zones. The precise depth-age curve of this isotherm depends on the thermal model used. Beneath the continents, the lithosphere is older and hence thicker, 100-250 km depending upon the age of the lithosphere. However, other models suggest that the LAB could be a boundary between dry, depleted mantle above a hydrated and more fertile mantle (Hirth and Kohlstedt, 1996; Karato, 2012). Since continents have gone through a complex geological history, the precise depth of the LAB is rather poorly defined. Therefore, here we focus on the oceanic lithosphere where different models of evolution of the lithosphere can be tested and verified. These results can then be used to understand the nature of the continental lithosphere as well.
The most direct evidence of the base of the lithosphere has come from surface wave studies where the lithosphere is associated with a high S-wave velocity above a low velocity and high attenuation asthenosphere (Priestley and McKenzie, 2006; Eaton et al., 2009) with a gradual decrease in the velocity (Figure 2). One of the limitations of surface wave tomography is that surface wave alone cannot distinguish a change in mantle velocity that occurs instantaneously in depth from a change that occurs over tens of kilometres. For example Eaton et al. (2009) have shown that a typical fundamental mode surface wave data can be fitted by a sharp LAB at 160 km or a transition zone from 125 to 225 km. Body wave tomography can be used to estimate lithosphere thickness, but since the waves travel vertically, there is a trade-off between velocity and thickness, and therefore uncertainty could be more than 20 km (Tan and Helmberger, 2007).
Recently, the mode-converted waves (P to S (Ps) and S to P (Sp)) from a sharp boundary have been used to determine the depth of the boundary and its velocity gradient. All these phases are primarily sensitive to changes in shear-wave velocity structure (either shear-wave velocity or impedance), and hence provide better resolution than surface waves. Rychert et al. (2005) inverted both Ps and Sp waveforms and found that a velocity drop across a LAB of 5-8% in <11 km zone is required. Similar studies have been carried out by several authors such as Kawakatsu et al. (2009) (Figure 3), Rychert and Shearer (2009), Schmerr (2012), but these results do not fit with the conventional understanding of the LAB (Priestley and McKenzie, 2006; Hirth and Kohlstedt, 1996; Faul and Jackson, 2005; Karato, 2012), which have led to heated debates about the plate tectonics and geodynamical processes.
In the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PiLAB) phase 1 our goal is to provide in situ passive seismic and electromagnetic constraints on the structure of the Lithosphere-Asthenosphere system on young seafloor (<40 Ma) as part of a large international multidisciplinary experiment to characterize the oceanic lithosphere in the Atlantic. The goal of the experiment is to use complementary information from different geophysical techniques (active and passive seismic, electromagnetic, shipboard geophysics and heatflow) to constrain at a high resolution the material properties of the lithosphere and asthenosphere. This will allow us to address fundamental questions about the evolution of oceanic lithosphere-is it thermally controlled or is it a compositional boundary, or does its rheological behavior transition with age between the two? For the asthenosphere we will be able to determine whether its relative weakness, high conductivity and low seismic velocity are caused by increased melt, hydration or if it is purely thermally controlled.
For the first phase of the experiment, we will deploy 30 broadband ocean bottom seismometers to image the crust and upper mantle down to 300 km using passive seismic techniques and 3 Magnetotelluric instruments to measure ressitivity. We will use surface and body waves to determine the isotropic and anisotropic structure of the crust and upper mantle, we will use converted phases to determine the character and depth of the LAB and other upper mantle discontinuities. We will also use shear wave splitting to determine azimuthal anisotropy across the region. We will construct 1-D resistvity profiles at 0, 25 and 40 Ma seafloor.
Our colleagues in France (IPGP) are already funded to perform an active seismic experiment designed to image the LAB and upper mantle structure from 0-100 Ma seafloor, as well as performing compliance measurements to determine the shear velocity structure of the crust and upper mantle. Our colleagues in the US (Scripps Instituiton of Oceanography) have applied for funding to perform active and passive electromagnetic studies along the same transects. Finally, our colleagues in Germany (GEOMAR) have applied for funding to do complementary high resolution electromagnetic, heat flow and active source experiments.
We are requesting shiptime to deploy 30 broadband instruments from the UK (15), French IPGP (9) and German DEPAS (6) ocean bottom seismometer pools. Figure 1 shows the array geometry for our 2 phase deployment (green triangles show locations of stations for phase 1, red phase 2, and black circles EM). After the success of phase 1 we will request funds for an additional passive deployment to cover 30-80 Ma seafloor.
Summary of Facility Requirements: We will be deploying 30 broadband ocean bottom seismometers provided by the OBSIP pool, and 30-40 OBEM from PI Constable at Scripps Oceanography. We will need Crane or A frame for deployment of equipment.

Ideally would would also run underway geophysical equipment, gravity, swath bathymetry, magnetometer, and sidescan sonar and technical support.

We will need lab space for prepping equipment and/or deck space to facilitate shipping containers for the OBS and OBEM equipment.
Summary of other requirements and comments:  
Ship Request Identification
Type of Request: Primary Ship Use Request Status: Submitted
Request ID: 1007866 Created By: Catherine A. Rychert
Date Last Modified: 7/28/2015 4:33:00 PM Date Submitted: 7/16/2015 7:17:00 AM
Requested Ship, Operating Days and Dates
Year: 2016 Ship/Facility: Marcus Langseth
Optimum Start Date: 1/1/2016 Dates to Avoid: No dates to avoid.
Earliest Start Date: 1/1/2016 Multi-Ship Op: No
Latest Start Date: 3/31/2016 Other Ship(s):

Operating Days Needed: Science Days Mob Days De-Mob Days Estimated Transit Days Total Days
17 2 2 8 29
Repeating Cruise?
(within same year)
No Interval:   # of Cruises: 1

Description of Repeating cruise requirements:
Justification/Explanation for ship choice, dates,
conflicts, number of days & multi-ship operations:
Work Area for Cruise
Short Description of Op Area
for use in schedules:
OBS deployment
Description of Op Area: Mid Atlantic Ridge to 40 Ma seafloor.
Op Area Size/Dia.:  
  Lat/Long Marsden Grid Navy Op Area
5° N / 25° W map
3 map
NA10 map
5° S / 10° W map
301 map
SA01 map
  Show Degrees Minutes    
Foreign Clearance and Permitting Requirements
Foreign Clearance Required? Yes Coastal States:

United Kingdom
 Important Info on Foreign Research Clearances  

Are you or any member in your science party bringing in any science equipment items which are regulated for export by the International Traffic in Arms Regulations (ITAR) and/or the Export Administration Regulations (EAR)?
No If yes, have you applied for the necessary permits through your export control office? No
 Questions about ITAR/EAR regulations?

Comments about foreign clearance requirements or
description of any other special permitting requirements
(e.g., MMPA, ESA, IHA, Marine Sanctuaries, etc.)
Port Calls
Requested Start Port Intermediate Port(s) Requested End Port
Praia, Sao Tiago, Cape Verde Islands None Praia, Sao Tiago, Cape Verde Islands
Explanation/justification for requested
ports and dates of intermediate stops
or to list additional port stops

 Important Info on Working in Foreign Ports

Science Party
Chief Scientist: Catherine A. Rychert, UoS
# in Science Party 12 # of different science teams 1 # Marine Technicians to be
provided by ship operator:
(include in science party total)
Explanation of Science Party Requirements and Technician Requirements The berths are for watchstanders/PI for underway geophysics and for technicians for the OBS and OBEM deployments.
Instrumentation Requirements That Impact Scheduling Decisions
Unselected Dynamic PositioningUnselected ADCPUnselected MultibeamUnselected Seismic
Unselected Dredging/Coring/Large Dia. Trawl WireUnselected Stern A-frameUnselected Fiber Optic (.681)Unselected 0.680 Coax Wire
Unselected SCUBA DivingUnselected Radioisotope use - briefly describeUnselected NO Radioisotope use/Natural level workUnselected Other Operator Provided Inst. - Describe
0 PI-Provided Vans - briefly describe Unselected MOCNESS  
Explain Instrumentation or Capability
requirements that could affect choice
of ship in scheduling.

Major Ancillary Facilities (that require coordination of schedules with ship schedule)
Unselected Helicopter Ops (USCG)Unselected Twin OtterUnselected Unmanned Aerial Systems (UAS) 
Autonomous Underwater Vehicle (AUV)
Unselected Other AUVUnselected Sentry  
Coring Facility
Unselected Jumbo Piston CoringUnselected Large Gravity Core Unselected MC800 multicorer w/ MISO camera/telemetryUnselected OSU Coring Facility (MARSSAM)
Unselected Other Large Coring FacilityUnselected WHOI Long Core  
Human Occupied Vehicle (HOV)
Unselected AlvinUnselected Clelia (HBOI)Unselected JSL I & II (HBOI)Unselected Other HOV
Other Facility
Unselected MISO Facility - deep-sea imagingUnselected Other FacilityUnselected Potential Fields Pool Equipment 
Remotely Operated Vehicle (ROV)
Unselected JasonUnselected Other ROV  
Seismic Facility
Unselected Ocean Bottom Seismograph Instrument Center (OBSIC)Selected Ocean Bottom Seismograph Instrument Pool (OBSIP)Unselected Ocean-Bottom Seismometer Program (UTIG)Unselected Other Seismic/OBS Facility
Unselected PASSCALUnselected Portable MCS groupUnselected Portable MCS/SCS groupUnselected U.S. Geological Survey Ocean Bottom Seismometer Facility (USGS at WHOI)
Towed Underwater Vehicle
Unselected ARGO IIUnselected Hawaii MR1 (HMRG)Unselected IMI12 (HMRG)Unselected IMI120 (HMRG - formerly DSL 120A)
Unselected IMI30 (HMRG)Unselected Other Towed Underwater VehicleUnselected Towfish 
UNOLS Van Pool
Unselected AUV Lab Van #1Unselected Clean Lab VanUnselected Cold Lab VanUnselected General Purpose Lab Van
Unselected Radioisotope Lab VanUnselected Wet Lab Van  
UNOLS Winch Pool
Unselected Mooring SpoolerUnselected Portable WinchUnselected Turn Table 
Explain Major Ancillary Facilities
Requirements and list description
and provider for "other" systems.

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