Projet COLMEIA

MARINE GEODESY
QUESTION :
 Is the Istanbul-Silivri fault segment creeping freely ? At what
rate ?
 Or is the fault segment blocked, accumulating elastic
deformation that may be released during a next major and
damaging earthquake ?
Marine geodetic measurements
Marine geodetic methods aim to monitor continuously or repeatedly 3D seafloor
deformation: rates of motion along the fault, recurrence of events, fault stress loading…
Questions :
 Is the Istanbul-Silivri segment of the North Anatolian Fault blocked ?
• aseismic creeping ?
• fully or partially locked fault ?
 Characterization of fault movements:
• nearly continuous ? Discontinuous ?
• rate ? few mm/yr (in case of creeping) to several tens meters in few hours (in case of co-sesiic
displacement) ?
 If the fault is fully or partially lock, evaluation of the stress loading
 ground deformation due to stress loading
Marine geodetic methods
 Horizontal movements
1. Acoustic ranging : acoustic wave travel time between
Precise Transponders (PXP)
 sub-continuous
 relative distance
 repeatability : 2 mm over a 750m -long baseline
(ex. Osada et al., 2008)
2. Acoustic/GPS combination (GPSA)
 discontinuous (1 position measurement / cruise)
 absolute positioning
 precision : 4-6 mm in 80h of triangulation
(ex. Chadwelll & Spiess, 2008; Juan de Fuca)
Acoustic ranging method for relative distance
measurements
 Vertical movements : bottom pressure
V. Ballu, Univ. La Rochelle
Acoustic/GPS method for absolute positioning
 Work plan
2013 :
 instrument integration (clinometers, compass, pressure, T…)
 acoustic signal detection method (frequency content & waveform of the signal)
 tests at sea : evaluation of resolution, precision, masks for diffraction, reflection
 processing tools
2014/2015 :
 1st deployment of 4 PXPS : Marmara Sea (R/V Pourquoi Pas ? PI. L. Géli Ifremer)
 Objective : Monitor Istanbul-Silivri segment of the North Anatolian Fault (NAF), south of Istanbul
• the NAF has been progressively rupturing along most of its length
• the Istanbul-Silivri segment might be the next to rupture
• highest level of seismic and tsunami hazard in Europe
• onland GPS stations are too remote from the active fault to measure the ground velocities in its vicinity
and to assess the stresses currently building on the fault
* ENV.2012.6.4-2 Long-term
monitoring experiment in geologically
active regions of Europe prone to
natural hazards: the Supersite concept
16-FP7-ENV-2012-2-stage.
 Marine geodetic measurements in the Marmara to:
1. determine if the fault is locked, accumulating elastic deformation, or is creeping aseismically
2. in case the fault is locked, evaluate the mechanical coupling along the fault and the rate of interseismic stress build-up, which reflects the slip deficit that may be released during the next earthquake
Horizontal GPS velocities in comparison with velocities from a geomechanical model of elastic loading with unlocked and
locked faults (red arrows), with faults locked at -15 km. Modified from Hergert & Heidbach (2010)