active tectonic - lisa mcneill [compatibility mode]
TRANSCRIPT
Application of swath bathymetry to active tectonic problems:
Case study of the Gulf of Corinth, central Greece
Lisa McNeillC. Cotterill1, T. Henstock1, J. Bull1, A. Stefatos2, S. Hicks1,
R. Collier3, G. Papatheoderou2, G. Ferentinos2
1Southampton Oceanography Centre, University of Southampton, UK2University of Patras, Greece
3School of Earth Sciences, University of Leeds, UK
Gulf of Corinth:- Region of earthquake activity- Continental plate is rifting or breaking apart- The early stages of forming a new ocean basinThis study:- Detailed marine geophysical survey of offshore active
faults which generate earthquakes and allow extension to occur
- Determine future earthquake sources- Constrain how the rift deforms - better understand
models of rifting and how they evolve through time
INTRODUCTION & OBJECTIVES
1981 extensional fault earthquakerupture in Eastern Gulf of Corinth
Eastern Eliki fault,Western Gulf of Corinth- one side of the fault uplifts and one subsides
Data Acquisition
• Reson 8160 50 kHz Seabat multibeam sonar– 150° swath across track, 126 beams– DGPS-fed motion sensor (military grade Inertial
Measurement Unit, IMU) for calculation of sonar position/orientation
• CSP2200 Sparker and CSP300P Boomer seismic system:– 60-channel hydrophone– Applied Acoustics catamaran-based source
• Boomer, multi-channel streamer and multi-beam equipment:– part of high resolution geophysics consortium grant– Cardiff, Imperial (London), Southampton universities, UK
JULY 2003 WESTERN CORINTH RIFT SURVEY
• 50 kHz Reson 8160 swath bathymetry• Sparker seismic profiles across and long rift• Boomer seismic profiles of Aigion fault tip - pseudo 3D
800m
axialchannel
submarinecanyons
landslidescar
fault-controlledbasement
ridge
northernsub-basin
CGF
AF
DF
8160 SWATH BATHYMETRY
N
Perspective view to west, showing fault controlled ridges and the Canyon-channel systems transporting river sediments into the gulf basin
• Basin sediments tilt towards the north - controlled by S-dipping faults (S Eratini and Sub-channel on northern margin)• Half-graben geometry tilted to north at this location• Multiple active faults offshore and onshore - distributed deformation
(NEF-North Eratini; SEF-South Eratini; SCF-Sub-channel; AF-AigionCGF-Cape Gyftissa; WEF-Western Eliki; EEF-Eastern Eliki; DF-Derveni)
4 MAJOR FAULTS ACROSS RIFT ACCOMMODATE EXTENSION
1
23
4
INTERPRETATION
sub-basin
Using variations in sea level through time
• As amount of ice on the earth varies, sea level changes in elevation• This changes systematically as we pass from a glacial to a non-glacial period• The coastal shoreline we see today is also produced during a glacial period when sea level was up to 120 m lower• These shorelines are then displaced by active faults - their presentdepth tells us how fast the fault moves
SHORELINE SUBSIDENCE BY N ERATINI FAULT
– Shorelines were originally at 60-70 m below current sea level– They are now significantly deeper due to subsidence by the N Eratini
fault
– We compare these rates with other faults in the gulf– Suggests this fault moves at ~ 3-6 mm per year– Together the 4 major faults take up extension across the rift which
totals ~ 10-15 mm per year
Age (ka) Depth (m) Subsidence rate11-13 90-95 1.5 - 3.0 mm/yr~130 160-170 0.7 - 0.9 mm/yr~240 200-230 0.5 - 0.7 mm/yr~340 260-300 0.6 - 0.7 mm/yr~430? 320-350 0.6 - 0.7 mm/yr
Why is it important?• Earthquake and tsunami hazards
to local populations• Understanding tectonic processes
in continental rifts - how do they evolve to eventually produce new ocean basins?
AIGION FAULT• A detailed study of the end of one young fault to see how it grows with successive earthquakes • Pseudo 3D multi-channel Boomer seismic survey of the fault tip plus 8160 multi-beam• Lines spaced 25-100 m apart• 3D interpretation of data
2 km
Pantosti et al, unpublished
Multi-channel boomer seismic data - example
Section across tip of extensional normal fault - Aigion fault
N S
• Major active faults are identified offshore as well as onshore• Multi-beam data constrain their surface geometry and indicate
recent activity (displacing young sediments on seafloor)• Sub-surface seismic data provide cross sections of faults
systems and allow low-stand shorelines to be identified -constrain rate of displacement on faults
• Multi-beam data resolve sediment transport systems and indicate how they are affected by active fault systems
• Combined datasets:– Resolve the geometry of the rift system in space and time– Constrain models of the evolution of rift systems– Indicate active faults with the potential to generate damaging
earthquakes and tsunamis (very common in the historic and archaeological record)
– Understand how faults grow and interact in space and time with sequential earthquakes
CONCLUSIONS
Aora cruise, Outer Hebrides Le Bas et al
SOC, University Marine Biological Station, Scotland,Scottish Natural Heritage,
Joint Nature Conservation CommitteeQueen’s University Belfast
Dept Agriculture and Rural Development, Belfast
OBJECTIVESMarine habitat mappingReconnaissance survey for futuresampling and camera tows