Constraining epistemic uncertainties on hazard models in the Marmara region using SHERIFS (Seismic Hazard and Earthquake Rates in Fault Systems)

Thomas Chartier, Oona Scotti, & Hélène Lyon-Caen

Published August 7, 2018, SCEC Contribution #8312, 2018 SCEC Annual Meeting Poster #028

Modelling the seismic potential of active faults and the associated epistemic uncertainty is a fundamental step of probabilistic seismic hazard assessment (PSHA). SHERIFS (Seismic Hazard and Earthquake Rate In Fault Systems) is an open-source code allowing to build hazard models including earthquake ruptures involving several faults (or Fault-to-Fault FtF ruptures) while exploring epistemic uncertainties. Following the findings of UCERF3, SHERIFS considers a system level approach but doesn't rely on an inversion and instead applies an iterative approach following three rules: (1) the FtF ruptures allowed in the fault system are defined as input by the user, (2) the slip-rate budget attributed to each fault section is preserved in the calculation, and (3) the magnitude frequency distribution (MFD) of the modeled seismicity in the fault system must follow an imposed shape. SHERIFS is built to be as user-friendly and versatile as possible for an easy exploration of epistemic uncertainties on a wide range of tectonic settings. The SHERIFS methodology is applied to the North Anatolian fault (NAF) system exploring uncertainties concerning the creep condition of the fault, the maximum size of rupture in the system and the target shape of the MFD. SHERIFS contains a number of visualization tools that allows to compare the modeled earthquake rates for each branch of the logic tree to the rate calculated from the earthquake catalog and to the ratio of aseismic slip that was needed to be considered in order to respect the three rules. The comparison with the data allows discussing both the fundamental input hypotheses as well as to select and weight the set of seismic hazard models that represents the range of uncertainty on the hazard assessment. This comparison reveals that in the Marmara region, models considering a 50% coupling of the NAF in the western Marmara Sea and using a “bump” MFD with a larger rate of large magnitude earthquakes compared to the Gutenberg-Richter distribution and ruptures potentially larger than the M7.4 1999 Izmit earthquake agree best with the earthquake rates calculated from the earthquake catalog and the paleo-earthquake record. The impact of each epistemic uncertainty on the hazard level for the city of Istanbul will be presented. An illustration of similarities and differences between SHERIFS and UCERF3 will also be presented with an example on the Death Valley fault system.

Key Words
fault systems, hazard, earthquake rate, modelling

Citation
Chartier, T., Scotti, O., & Lyon-Caen, H. (2018, 08). Constraining epistemic uncertainties on hazard models in the Marmara region using SHERIFS (Seismic Hazard and Earthquake Rates in Fault Systems). Poster Presentation at 2018 SCEC Annual Meeting.

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