Comparison of probabilistic fault displacement hazard assessment results with observed permanent ground displacements in the aftermath of the 6 February 2023 Kahramanmaras Turkiye Earthquake.

Abstract

The continuous functionality of critical infrastructure such as oil, gas, and water pipelines, as well as tunnels and bridges following an earthquake is important for the effective management of response actions and influences the seismic resilience of communities. Failure of such infrastructure may result in injuries and human fatalities, environmental pollution as well as significant direct and indirect economic losses. One of the most catastrophic earthquake-induced actions is the permanent fault displacements observed when fault ruptures propagate up to the ground surface in case of large magnitude earthquakes. Any structure but mostly pipelines, tunnels and bridges crossing active faults are prone to such permanent fault displacements as they develop excessive deformations as a result. The earthquake resistant design of pipelines, tunnels and bridges is based on reliable estimation of such excessive deformations. 6 February 2023 Kahramanmaras Turkiye Earthquake with Moment Magnitude 7.8 (United States Geological Survey, USGS) ruptured 3 consecutive segments of the East Anatolian Fault Zone: namely Amanos, Pazarcik and Erkenek segments. East Anatolian Fault Zone is one of the most active strike-slip faults in the world. The total observed surface rupture as a result of the Kahramanmaraş Earthquake exceeded 300km with measured permanent displacements reaching 5m near Kahramanmaras and diminishing to 0.5m towards South and North. In this study, by carrying out probabilistic fault displacement hazard assessment for these segments of the East Anatolian Fault Zone expected permanent fault displacements were computed as a function of return period. Influence of multi-segment rupture, selected earthquake recurrence model, adopted maximum magnitude value are studied on the computed permanent displacement results. Computed displacements are critically compared against the observed permanent displacements. Pipeline Systems and Liquid Storage Tanks Earthquake Code of Turkey (2021) and EN1998-4:2006 suggest the use of empirical fault rupture length-permanent fault displacement relationships in design of pipelines crossing active faults. prEN 1998-4:2022 however suggests an alternative methodology that allows approximate calculation of permanent fault displacements corresponding to any given return period based on fault mechanism, fault rupture length and fault productivity. These code-based estimates are compared with measured fault displacements and conducted probabilistic fault displacement hazard results.