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

PLATE TECTONICS OF E. MEDITERRANEAN

CORINTH RIFT, CENTRAL GREECE

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

1861 earthquake,

Eliki Fault

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

Multibeam Setup

Courtesy of Tim Le Bas, SOC

8160 sonar and the MV Vassilios G

Boomer/sparker seismic sources

Custom 60 channel x1m streamer, Geometrics recording system

Deployment of the multi-channelstreamer for seismic dataacquisition

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

NORTHERN SUB-BASIN, SPARKER LINE 11

NORTHERN SUB-BASIN, SPARKER LINE 11

~130 kashoreline

NORTHERN SUB-BASIN, SPARKER LINE 10

NORTHERN SUB-BASIN, SPARKER LINE 10

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

Aigion fault

8160 multi-beam data- 1.5 m grid cell

2 km

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

8101 multi-beam

8101 backscatter

500 m

Detail of multi-beam and backscatter

Evidence of SW-NE current directionsSand and gravel waves

Archaen age bedrock dominatesbathymetric highs