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Abstract:
The main Marmara fault (MMF) extends for 150 km through the Sea of Marmara and
forms the only portion of the North Anatolian fault zone that has not ruptured in a large
event (Mw > 7) for the last 250 yr. Accordingly, this portion is potentially a major source
contributing to the seismic hazard of the Istanbul region. On 26 September 2019, a
sequence of moderate-sized events started along the MMF only 20 km south of
Istanbul and were widely felt by the population. The largest three events, 26 September
Mw 5.8 (10:59 UTC), 26 September 2019 Mw 4.1 (11:26 UTC), and 20 January 2020 Mw 4.7
were recorded by numerous strong-motion seismic stations and the resulting ground
motions were compared to the predicted means resulting from a set of the most recent
ground-motion prediction equations (GMPEs). The estimated residuals were used to
investigate the spatial variation of groundmotion across theMarmara region. Our results
show a strong azimuthal trend in ground-motion residuals, which might indicate systematically
repeating directivity effects toward the eastern Marmara region.
