Seismotectonics of Turkey and Iran from calibrated earthquake relocations

Abstract

Uncertainties in earthquake hypocenter locations, which are counted in tens-of-kilometers in most regions of the world, are a serious limitation to seismotectonic studies. For example, they preclude individual events from being confidently attributed with mapped surface faults, complicate the study of mainshock-aftershock sequences and triggering behavior, and errors in depth are problematic for establishing the mechanical and rheological properties of the crust. These errors mostly arise from unknown Earth velocity structure. Well-established relative multiple-earthquake relocation techniques help eliminate these errors, but it remains challenging to achieve minimally biased absolute ('calibrated') locations. In this thesis, I use an advanced multiple-earthquake relocation technique that utilizes calibration of discrete clusters of earthquakes (100s of events over spatial scales <100 km) by exploiting near source data, aftershock deployments and InSAR observations. The three body chapters consist of independent journal manuscripts connected by this common theme. The final chapter presents ongoing work on implementing these trusted, calibrated locations as prior constraints to relocate a much larger dataset over a wider region (1000s of events across ~1000 km) using Bayesian methods. Our results show how calibrated earthquake locations can be employed to transform our understanding of the kinematics of faulting in Iran and Turkey, and also to improve interpretations of the associated seismic hazard. Both regions have a long history of very destructive earthquakes, and nearly one third of the deadliest earthquakes since 1900 have occurred within our study area. The Zagros mountains, which are the focus of Chapter 4, are of huge economic, social and cultural importance to Iran, containing vast oil and gas reserves, its two major nuclear reactors, six UNESCO World Heritage Sites, and several large cities. Therefore, our results are of clear interest in both countries, which also helped to develop new international collaborations with local seismologists. Finally, our new two-tiered relocation procedure, once fully developed, can be transferable to other regions requiring more precise epicentral locations.