Surface Fault Breaks, Aftershock Distribution, and Rupture Process of the 17 August 1999 Izmit

Abstract

Rupture process analysis suggests two stages of rupture separated in space and time, with an estimated total scalar seismic moment of 2.42 X 10(20) N in. The first stage initiated at the epicenter, near Izmit, and propagated asymmetric ally-first eastward and then westward with a total scalar moment of 1.6 X 10(20) N in, showing predominantly right-lateral strike-slip faulting followed by a minor subevent extending the rupture further east. The second stage took place at the western and eastern ends of the source area, rupturing two segments within the Marmara Sea, west of the Hersek Delta, and two segments between Akyazi and Golyaka. The rupture process analysis indicates that six fault segments were ruptured during the mainshock: four of them on land and two within the Marmara Sea. The major moment release of 1.2 X 10(20) N m is found on the 64-km-long Sapanca segments located between the easternmost tip of the Gulf of izmit and Akyazi, with an estimated maximum slip of 5.3 in. The moment release on the Golcuk segment, with a length of 30 km, is about 3.7 X 10(19) N in, and the estimated slip on this segment is 4.1 in. Rupture process analysis suggests two 20-km-long segments between Akyazi and Golyaka striking N70degreesE. The scalar moment releases on these segments are 2.7 X 10(19) and 1.9 X 10(19) N in, with estimated offsets of 2.2 and 1.6 in, respectively. The last two subevents took place to the west of the Hersek Delta on the Yalova segment and within the Marmara Sea, with estimated offsets of 1.3 and 1.0 in, respectively.