The disastrous 1999 earthquakes in Turkey have stimulated the international commu- nity to understand the geometry and the behaviour of the North Anatolian Fault (NAF) beneath the Marmara Sea. Whereas the area is considered mature for a large earth- quake, the detailed fault geometry below the Marmara Sea is uncertain, preventing a realistic assessment of seismic hazards. We have recently conducted two geolog- ical/geophysical surveys in the Marmara Sea. We carried out high resolution multi- beam bathymetry, high-resolution CHIRP sub-bottom and multichannel seismic re- flection profiling, magnetometry, and bottom imaging with a remotely-operated vehi- cle (ROV). Over 60 gravity and piston cores were collected. Our main objectives were to identify and date fault ruptures on the seafloor, define the spatial-temporal distribu- tion and the style of deformation and tectonic movements in this portion of a major continental strike-slip boundary. We have obtained accurate sea-bottom topography and shallow subbottom profiles over key portions of the eastern Marmara Sea. We have successfully located faults with an accuracy of 1-2 m. Some faults offset resolv- able layers in the late Holocene and thus probably ruptured the surface in some earth- quakes. We found direct evidence of surface rupture in the cores targeting a branch of the transform near western cost of Hersek Peninsula, in the Ganos region and in the Central basin of the Gulf of Izmit. Morphological maps of the base of the Holocene sediments were obtained by close space grids of chirp profiles acquired in selected key areas. Layer picking was performed on the basis of seismo-stratigraphy (seismic facies and geometries), as well as through the analysis of reflectivity maps. We studied three sedimentary and topographic features that define piercing lines useful both to es- timate the slip along the fault and to reconstruct the post-glacial paleo-oceanographic history of the Marmara Sea. These features, a 85-m-deep paleo-shoreface, a canyon and a buried river channel, are displaced along the NAF system. The detailed 3-D re- construction of their geometry and C-14 datings will allow us to estimate Holocene slip rates and hopefully identify individual earthquakes on fault segments of the North Anatolian plate boundary.
Exploring submarine earthquake geology in the Marmara Sea: slip rate of the North Anatolian Fault and geological record of earthquakes
A Polonia;L Capotondi;L Gasperini;
2002
Abstract
The disastrous 1999 earthquakes in Turkey have stimulated the international commu- nity to understand the geometry and the behaviour of the North Anatolian Fault (NAF) beneath the Marmara Sea. Whereas the area is considered mature for a large earth- quake, the detailed fault geometry below the Marmara Sea is uncertain, preventing a realistic assessment of seismic hazards. We have recently conducted two geolog- ical/geophysical surveys in the Marmara Sea. We carried out high resolution multi- beam bathymetry, high-resolution CHIRP sub-bottom and multichannel seismic re- flection profiling, magnetometry, and bottom imaging with a remotely-operated vehi- cle (ROV). Over 60 gravity and piston cores were collected. Our main objectives were to identify and date fault ruptures on the seafloor, define the spatial-temporal distribu- tion and the style of deformation and tectonic movements in this portion of a major continental strike-slip boundary. We have obtained accurate sea-bottom topography and shallow subbottom profiles over key portions of the eastern Marmara Sea. We have successfully located faults with an accuracy of 1-2 m. Some faults offset resolv- able layers in the late Holocene and thus probably ruptured the surface in some earth- quakes. We found direct evidence of surface rupture in the cores targeting a branch of the transform near western cost of Hersek Peninsula, in the Ganos region and in the Central basin of the Gulf of Izmit. Morphological maps of the base of the Holocene sediments were obtained by close space grids of chirp profiles acquired in selected key areas. Layer picking was performed on the basis of seismo-stratigraphy (seismic facies and geometries), as well as through the analysis of reflectivity maps. We studied three sedimentary and topographic features that define piercing lines useful both to es- timate the slip along the fault and to reconstruct the post-glacial paleo-oceanographic history of the Marmara Sea. These features, a 85-m-deep paleo-shoreface, a canyon and a buried river channel, are displaced along the NAF system. The detailed 3-D re- construction of their geometry and C-14 datings will allow us to estimate Holocene slip rates and hopefully identify individual earthquakes on fault segments of the North Anatolian plate boundary.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
