The causes of deep-focus earthquakes, those below about 350 km, remain a subject of much debate. The high pressures at such depth preclude frictional sliding seen in shallower earthquakes, and water has been almost entirely squeezed from the voids. Several theories have been proposed. One of the most promising is that of transformational faulting. It is hypothesized that olivine minerals in the descending slab transform into spinel at high temperatures and pressures. Under the right conditions, these transform in narrow, weak bands propagating from stress concentrations. We examine this hypothesis by creating an enhanced finite element model that includes thermal and phase change effects. Phase transformation is model as a rate process dependent on stress and temperature, following [1]. Under certain conditions, the phase transformation is likely to localize into weak bands, and we examine the mathematical conditions that allow this. The localized band are inserted into the enhanced finite element framework. We start by modeling small-scale laboratory experiments at high pressure and temperature, such as those in [2]. The model will then be upscaled to a fault-scale model, to see if the type of events observed can be reproduced, focusing on the central Japan fault zone. [1] S. Sindhusuta, S.W. Chi, C.D. Foster, T. Officer and Y. Wang, “Numerical Investigation into Mechanical Behavior of Metastable Olivine during Phase Transformation: Implications for Deep-Focus Earthquakes.” In review [2] Y. Wang, L. Zhu , F Shi, A. Schubnel, N. Hilairet, T. Yu, M. Rivers, J. Gasc, A. Addad, D. Deldicque, Z. Li, and F. Brunet “A laboratory nanoseismological study on deep-focus earthquake micromechanics”. Science advances, 2017. 3(7): p. e1601896.