RAPID/Collaborative Research: Advancing Probabilistic Fault Displacement Hazard Assessments by Collecting Perishable Data from the 2023 Turkiye Earthquake Sequence

点击翻译按钮获取中文摘要

The 300-km-long magnitude (M) 7.8 earthquake rupture along the East Anatolian Fault in Türkiye is one of the largest strike-slip ruptures instrumented globally. At the same time, the 150-km-long M7.5 rupture of the largest aftershock on the Sürgü fault, produced surface displacements on the order of 8 m, exceeding, on average, the displacement-length relations used for the 2023 National Seismic Hazard Model (NSHM) update by more than fifty percent. These ruptures share a similar tectonic setting with the San Andreas Fault System (SAFS) in California, so evaluating the NSHM by comparison with the Türkiye fault ruptures is important in the context of risk reduction in the US. A similar rupture on the SAFS, often referred to as 'The Big One' in California, will threaten the population and economy of major urban centers, national defense installations, and other critical infrastructures. Observing and documenting displacements along these exceedingly long and rare ruptures is therefore critical to understanding and reproducing earthquake rupture processes, empirically and numerically; to reducing uncertainty in regional hazard models; and reducing the risk of distributed infrastructure systems that are vital to the health and prosperity of communities, and vulnerable to ground deformation, such as water and gas pipelines. Findings and open-source datasets from this Grant for Rapid Response Research (RAPID) fieldwork will guide public policy and engineering design codes through future improvements of the NSHM, as well as decision makers for a greater extent of societal well-being and national defense. To complete this work, partnerships between academia and government agencies in both the US and Türkiye have been established; the team is diverse and includes a balance of early-career scientists and senior scientists, geotechnical earthquake engineers and earthquake geologists, US-based and in-country collaborators, and scientists from underrepresented backgrounds. The intellectual merit of this work lies in setting a new paradigm in fault rupture field mapping for engineering applications. While there is field, laboratory and numerical evidence that shallow geological conditions affect fault displacements, the evidence is at best qualitative, and thus the documented data cannot be integrated in engineering models for risk reduction. In order to capture these effects in predictive empirical models for engineering applications, new kind of dataset is needed that associates each fault displacement measurement site with geotechnical site characterization measurements. The primary field objectives include characterization of the 2023 ruptures by means of: (1) mapping the main fault rupture with high-resolution (cm-scale) GNSS surveys, photographs, ground-based lidar, and UAV-based terrain models, (2) documenting discrete and perishable offsets of cultural and geomorphic features, (3) characterizing the width and style of the deformation zone, (4) accompanying the measurements of the transient deformation zones with dynamic site characterization measurements on a sub-km scale using active source and ambient wavefield surface wave methods, along with horizontal to vertical spectral ratio (HVSR) measurements, (5) providing geological context (e.g., dominant geological processes and depositional units) for site characterization efforts, and (6) identifying secondary effects such as gravitational failures and liquefaction. Insights and scaling behaviors stemming directly from the field data will provide the first of what is envisioned to constitute the next-generation fault displacement datasets that will allow future PFDHA models to capture repeatable effects associated with local geologic conditions and fault geometry among other parameters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.