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Abstract:
The submarine Main Marmara Fault is overdue for an M>7 earthquake in the direct vicinity of the Istanbul megacity and is the only segment of the right-lateral North Anatolian Fault Zone that has not been activated since 1766. On 26 September 2019, an Mw5.7 earthquake occurred offshore Silivri (west of Istanbul), stimulating discussions on a future major earthquake. The predominant faulting style for this pending earthquake remains enigmatic. In this study, we investigate the coseismic rupture evolution of the 2019 Silivri earthquake and decipher the multi-type-faulting aspects by a nonstandard approach. The event was dominated by a large compensated-linear-vector-dipole component, of about -50% that we interpret as a consecutive strike-slip and thrust double-couple episode, closely collocated in space and time. Due to local variations of the fault geometry at the eastern boundary of the Central Basin, crustal shortening and related thrust-faulting are expected. A striking observation is the almost synchronous occurrence of both faulting types during a single earthquake. The earthquake complexity here is reported for the first time in the Sea of Marmara region and has to be considered in future rupture scenarios of an expected M>7 event, with subsequent consequences for tsunami hazard and risk.
