Quantifying the relationship between the Earth?s convecting interior, plate motions, and earthquakes in Alaska using three-dimensional numerical simulations

Purdue University, West Lafayette IN

Investigators

Abstract

It is important to understand the levels of mantle coupling that drives intraplate continental deformation, a fundamental question in geophysics, as it will aid in seismic hazard analysis for earthquakes that occur far away from plate boundaries. How mantle flow drives surface deformation and motions in oceanic lithosphere is well established and has been key in further understanding many aspects of plate tectonics, however, within intraplate continental lithosphere the quantification of this coupling remains poorly understood. Alaska provides a unique opportunity to assess the level of continental lithospheric/mantle coupling due to its thin lithosphere and surface motions that are not easily explained by relative plate motions and gravity acting on high topography. The diffuse Pacific - North America plate boundary zone in Alaska is related to the subduction of the Pacific plate and Yakutat microplate beneath the North American plate and clockwise rotation of the Bering plate to the west, and has been used as an analog for an early Tibet. Observed surface motions in Alaska, however, illustrate that it is unlike any other convergent continental plate boundary. For example, all convergence of the approximately 5 cm/yr of Pacific - North America relative plate motion is accommodated within a 500 km zone, and surface motions beyond this zone are directed southward towards the plate boundary. Because the of the long time scale over which significant intraplate earthquakes occur it is vital to understand how stress is transferred form the mantle into these regions, this study will to address that fundamental question This project will also support the research of a graduate and undergraduate student. We will perform 3-D finite element geodynamic modeling to investigate the role mantle flow in driving intraplate surface motions and deformation in Alaska. These numerical experiments will be constrained using geophysical observations and have a physically accurate model volume (geometry) for the diffuse Pacific-North American plate boundary zone in Alaska. The resolution of this 3D geometry will allow us to determine the level of coupling between the Alaskan lithosphere and convecting mantle beneath it. We will differentiate between physically viable models by comparing our various model's predicted surface velocities to the observed surface deformation field, constrained by GPS and Quaternary fault slip data, This work will seek to answer the following questions: (1) What are the driving forces of the Bering plate? (2) What are the relative contributions of lithospheric thickness, lithospheric rheology and mantle flow in driving intraplate deformation in northern and central Alaska? (3) What force(s) is/are responsible for compression and uplift of the Mackenzie Mountains?