A teleseismic finite-fault rupture model for the August 17, 1999, zmit earthquake (Mw = 7.6): implications for the seismic nucleation phase

A linear finite-fault inversion procedure is applied to teleseismically recorded broadband P and SH velocity waveforms of the August 17, 1999, zmit earthquake, to derive spatial and temporal distributions of the co-seismic slip over the representative three-segment model fault. The model fault is longer than the mapped surface rupture, and it extends offshore for 25 km in the west, to define the western end of the earthquake rupture. The teleseismically derived slip model suggests a bilateral rupture with a total seismic moment release of 2.6 ×1020 Nm, and that the rupture was dominated by failure of two major asperities with peak slip amplitudes reaching 7 m. The hypocentral area was represented by the relatively low displacement that separated the large asperities. In the west, the rupture reached the eastern entrance of the narc k basin beneath the Sea of Marmara, with an average slip of ca. 2 m. This indicates that the rupture propagated offshore for ca. 20 km after crossing Hersek Peninsula. The analysis also reveals that the total rupture process time was 32 s, while the main seismic moment release, which corresponded to the rupture of the two large asperities, occurred between 4 s and 16 s after rupture initiation. The strong wave energy arrivals from the failure of the large asperities were preceded by weak wave arrivals in the initial section of the teleseismic waveforms used in this study. Along with some observations from previous studies, this emergent onset of the wave arrivals prompts us to discuss the possibility of a seismic nucleation process for this earthquake.