Rupture characteristics of the A.D. 1912 Mürefte (Ganos) earthquake segment of the North Anatolian fault (western Turkey)

Abstract

Abstract: The Ganos fault is the westernmost segment of the North Anatolian Fault (NAF) that generated the 9 August 1912 Murefte (Ganos) earthquake (Mw=7.4). We study the 1912 earthquake characteristics using co-seismic fault slip and fault segmentation coupled with an analysis of historical seismic records. Surface ruptures with small releasing and restraining structures and 1.5 to 5.5 m right-lateral offsets have been measured at 45 sites of the onland ~45-km-long fault section. Similar structures are delineated by fresh fault scarps and prominent pull-apart basins in the Sea of Marmara and Saros Bay. A second shock with Mw=6.8 occurred on 13 September 1912 implying 20 to 40-km- long rupture; the damage distribution and analysis of seismic records suggest an epicenter located further west near Saros Bay, which indicates the location of western termination of the 9 August rupture. Our modeling of historical seismic records reveals a relative source time function between the two events and indicates a 40 second rupture duration, in agreement for a 120±30-km-long fault rupture for the 9 August shock. An estimated total rupture length of 150±30 km for the two earthquakes combined with onshore and offshore fault segmentation allow us to better constrain the western limit of the Marmara Sea seismic gap and related potential for producing a large earthquake that was sharply increased by the devastating 1999 Izmit earthquake in the east.