DEVELOPING TOOLS FOR PALEOSEISMOLOGY IN THE SUBMARINE ENVIRONMENT, CASE STUDIES: NORTH ANATOLIAN FAULT ZONE, MARMARA SEA, TURKEY AND EL PILAR FAULT, CARIACO BASIN, VENEZUELA

Paleoseismology is effective to study seismic activity along transform boundaries on land. However, many of these large transform faults occur beneath the sea. To assess seismic risk we are studying the North Anatolian Fault Zone (NAFZ) beneath the Marmara Sea, Turkey and the El Pilar fault in the Cariaco Basin, offshore Northern Venezuela.

High-resolution sub-bottom profiling (CHIRP), swath bathymetry and sediment-core analyses (grain size, organic carbon and calcium carbonate) permit to identify seismites that are then dated using short-lived radioisotopes and radiocarbon. Turbidites are identified and linked to the historical record of earthquakes. Turkey has a record dating back 2000 years and Venezuela 500 years. Events are correlated to the historical record of earthquakes to determine seismic activity along different segments of a fault.

Our initial studies along the NAFZ in the Marmara Sea have permitted to characterize a sea floor rupture and seismite in a small parasitic basin 40km from the 1912 Ganos epicenter (7.4Ma), and a major erosional event in the Tekirdag Basin, both related to the 1912 earthquake. Application of this technique appears to be promising for assessing risk in submarine settings adjacent to heavily populated regions.

We are beginning to develop a systematic method in which to characterize turbidites in the varved sediments of the Cariaco Basin. Logging the cores for bulk density, magnetic susceptibility and color spectra at a mm-scale enables comparisons to seasonal varve deposition, correlating the peaks to sandy/muddy intervals. The events are then dated.