Doctoral defence in Environmental studies - Farnaz Bayat

Doctoral candidate: Farnaz Bayat

Title of thesis: New earthquake fault system model of the Southwest Iceland transform zone and near-fault seismic ground motion model for earthquake engineering applications

Opponents: Dr. Aybige Akinci, Senior Researcher at National Institute of Geophysics and Volcanology, Rome, Italy

Dr. Freysteinn Sigmundsson, Research Scientist at the Institute of Earth Sciences, University of Iceland

Advisor: Dr. Benedikt Halldórsson, Research Professor at the Faculty of Civil and Environmental Engineering, University of Iceland

Other members of the doctoral committee:

Dr. Birgir Hrafnkelsson, Professor at the Faculty of Physical Sciences University of Iceland

Dr. Fabrice Cotton, Professor at the Institute of Geosciences, University of Potsdam, Germany

Dr. Milad Kowsari, Research Specialist at the Earthquake Engineering Research Centre, University of Iceland

Chair of Ceremony: Dr. Hrund Ólöf Andradóttir, Professor and Head of the Faculty of Civil and Environmental Engineering, University of Iceland

Abstract

Large earthquakes up to ~Mw7 repeatedly take place in the two transform zones of Iceland. Of the two, only the South Iceland Seismic Zone (SISZ) is on land and with a large part of the population in close proximity to it. Therefore, the seismic risk in Iceland is highest in the south and a reliable assessment of such risk is crucial. The basis for such an assessment is a meticulous and formal evaluation of probabilistic seismic hazard assessment (PSHA). Past PSHA in Iceland have, however, been based on statistical analyses of various historical catalogues and limited ground motion models (GMMs), all subject to varying types and degrees of uncertainties. Moreover, they relied on simplistic source descriptions and largely ignored that the unique ‘bookshelf’ strike-slip fault system of the SISZ extends along the plate margins towards the west and over the Reykjanes Peninsula Oblique Rift (RPOR). Namely, the bookshelf faults is twice as long as previously thought and it dominates the strain release of transcurrent plate motion, having potentially important implications for PSHA. Fortunately, the above limitations have effectively been addressed in this thesis through the development of a physics-based bookshelf fault system model of the SISZ-RPOR. The rate of tectonic motion across the zone along with the fault system geometry have been used to calibrate the model that also captures the variation of seismogenic depth along the zone. It allows random realizations of the fault system configuration where each fault is completely specified by its dimensions, maximum magnitude, and long-term slip rate, and moment rate. It also allows the derivation of subzone specific MFDs, the cumulative seismic activity of which is not only consistent with, but effectively explains the earthquake catalogue of the SISZ-RPOR. In particular, the ability of the model helps to generate realizations of long-term finite-fault catalogues for a physics-based Monte Carlo stochastic approach to PSHA. We therefore took advantage of the parametrization of a vast synthetic dataset of ground motion time histories in the SISZ-RPOR and augment the latest Bayesian GMMs for the region with a near-fault directivity term. We recalibrate the regression coefficients to the synthetic data using advanced Bayesian inference techniques. The Bayesian approach quantifies the probability distribution of each coefficient along with their uncertainties. The results of this study not only enable the efficient yet physically realistic and consistent revision of conventional time-independent PSHA for the SISZ-RPOR using e.g., empirical GMM, but also a more comprehensive physics-based PSHA which will be based on the same physical finite-fault system model.

About the doctoral candidate

Farnaz Bayat was born in Iran in 1991 and earned B.S. degree in physics in 2013 from Bu-Ali Sina University in Hamedan, Iran. Her undergraduate studies laid a solid foundation for her master’s degree in geophysics at the University of Tehran, Iran. She ranked first among 100 candidates in the 2017 Iranian national university entrance exam and began her Ph.D. in earthquake seismology at the University of Tehran, Iran.

She joined the University of Iceland in late 2019 as a doctoral candidate in Environmental Sciences at the Faculty of Civil and Environmental Engineering. Her studies were a part of the SENSHAZ, Rannis project led by Prof. Benedikt Halldorsson and Dr. Milad Kowsari.

During her Ph.D. studies, she developed a new finite-fault earthquake source model of the unique bookshelf transform fault system in Southwest Iceland. This model has a wide range of important applications, particularly in the field of physics-based seismic hazard assessment. Her work has involved numerous scientific collaborators and experts in engineering seismology and related fields, and is finding use in a current ongoing revision of seismic hazard in Southwest Iceland. It has also found use in European H2020 projects, most notably the Center of Excellence in Exascale in Solid Earth (ChEESE project), and informed the latest revision of the European Seismic Hazard Models (ESHM20) in Europe.