Transcript Theme 4

Earth in Motion Summary- Jim Mori, Laura Wallace
Proposals in the System:
Hikurangi slow slip- 781-MDP & 781A-Full, Riserless drilling and Observatory
Phase
Proposals in the process of being developed:
Hikurangi deep riser drilling phase
Ideas for New Proposals:
Brothers Volcano (Cornel de Ronde)
Tuaheni Slides (Ingo Pecher)
Porangahau Fluid Flow & Slow Slip (Ingo Pecher)
Near Trench Axis drilling-comparative study of Japan, Hikurangi, Costa Rica,
Sumatra (Shuichi Kodaira)
Proposals in Progress
Hikurangi Slow Slip
• Understand the causes of slow slip events
• Drilling target is an interface dominated by aseismic
creep (in distinct contrast to Nankai)
• Coring and logging will provide information about
physical conditions in region within and above slow
slip events. Incoming plate section will reveal
protolith of rocks in the SSE source further down.
• Monitoring changes in strain, tilt, seismicity, and
fluid pressure, flow rates, and geochemistry during
slow slip events
Comparison between Japan trench and Hikurangi—this
could make Hikurangi a compelling riser target to help
undertand Japan’s subduction zones
Yoshihiro Ito
Fault depth
Mw
3
Duration
Japan Trench
10 – 15 km
6.8 – 7.0
20 – 40 days
Hikurangi
5 – 15 km
6.5–6.8
14 – 35 days
Main discussion points for further developing
Hikurangi slow slip project
Riser proposal to reach source of slow slip events ( ~ 5.5 km )
• Identify fault(s) of large earthquakes and slow slip events
• Great interest in physical mechanisms, friction characteristics,
fluid conditions, comparisons to other regions (Tohoku)
• Important to obtain sample of fault zone (difficult coring)
• Fluid and Pressure monitoring in deep borehole
• Need some casing deformation measurement
Plan to submit riser proposal in April 2013
Need to coordinate funding for observatory (riserless and riser),
3-D site survey, 3D VSP, OBS+pressure gauge deployment
New Ideas for proposals
Brothers Volcano- Cornel de Ronde
Volatiles coming to seafloor, end members of flow
rates and fluid composition at one volcano
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Caldera formation
Exsolved gas from magma
Formation of hydrothermal minerals
Biological communities
Workshop in Europe in November
Proposal submission in April 2013?
New Ideas for proposals
Tuaheni Slides- Ingo Pecher
Possible slow moving landslides in region of proposed781-A
drilling transect
Over pressured fluids and gas from hydrates may
cause hydrofractures, producing landslide planes
in regions of hydrates
(Usually BSR are thought to be slide plane)
• Mechanisms of slides
• Role of overpressurization from hydrates
MeBo, R/V Sonne 70? m cores scheduled in 2015?
APL Proposal for 150-200 m boreholes, LWD and pressure cores
New Ideas for proposals
Porangahau Ridge Fluids (central Hikurangi margin)
Large scale gas volumes outside of GHSZ (Gas Hydrate Stability
Zone)
South of Hikurangi proposal area, slow slip interval different
more fluids
Episodic slow slip events may cause fluid flow.
Transient fluid flow suspected from heat flow anomaly, resistivity,
seismic velocities.
• Constrain fluid flow budgets, fluid sources during slow-slip
• Test model
Propose boreholes with LWD (temperature), pore water chemistry,
pressure cores, observatory (too much for APL?). Could this be a
MeBo (+MeBo observatory), or potentially a future (well down the
track) JR proposal? Probably needs more surface investigations.
Seafloor thermal gradient
Massive discrepancy to BSR thermal gradient
May point towards transient anomaly (i.e., advective heatflow pulse)
(but may be caused by bottom-water temp. fluctuations)
(Plaza Faverola et al., in prep.)
Slow-slip
Transient fluid-flow anomaly,
Possible fluid
migration paths Fluids probably from depth
of subduction interface
New Ideas for proposals
Comparisons of near trench axis drilling – Shuichi Kodaira
(Hikurangi, Tohoku, Nankai, Costa Rica, Sumatra)
Drilling of sediments at toe of thrust preserves
history of previous earthquakes
Shallow holes (~100-200 meters) and piston coring
• Understand the near trench earthquake rupture history
• Slip behavior of splay faults (vitrinite reflectance, turbidite
paleoseismology, others?)
• Need to modify current conceptual model for subduction
interface behavior and shallow seismic faulting on megathrust
• Slip in this region controls tsunami size
• Importance for hazards
Alternate site HSM10-A in 781-A near toe, could drill ~200 m during
drilling for 781-A. Submit MSP proposal to use MeBo to do along
strike transect of ~200 m cores through Hikurangi toe
Along trench axis drilling transect to spatial
and temporal record of slip-to-the –toe
earthquake
IODP
Trench-filled sediment preserve a long term record of slipto-the-toe earthquake
Slip at a toe in the Nankai Trough
Sakaguchi et al., 2011
High vitrinite reflectance;
evidence of frictional heating
at the frontal thrust
• Is there evidence for slip
to the toe at Hikurangi?
• Would also provide a
nice compare/contrast
to Nankai (south
Hikurangi) and Tohoku
(north Hikurangi)
• Potential for tying this
into a global study of
near-trench seismic
behavior (Sumatra,
Costa Rica, others?)
• Hikurangi cores could be
done with MeBo as a
MSP proposal+during
781-A leg for N.
Hikurangi
Proposals in progress/new ideas
What to do?
Hikurangi Riser proposal
Develop and submit riser proposal in
April 2013
Brothers Volcano
Workshop in Europe, November 2012.
Possible JR pre-proposal (or full proposal
if mature enough??) for April 2013.
Tuaheni Slides (Hikurangi margin)
Submit APL for 781-A drilling. MeBo
coring will happen in the area in 2015
Porangahau Fluids
Possible MeBo proposal? Ideas around
this still need some development. May
require some form of observatory.
Comparative trench axis study: alongstrike transect of Hikurangi thrust front
Submit MSP proposal (to use MeBo)+we
will try to do shallow drilling (~200 m) at
north Hikurangi toe during the 781-A
riserless drilling