The mechanical deformation of sea ice has substantial influence over large-scale (e.g., > 10 km) ice properties, such as the ice thickness distribution, as well as small-scale (e.g., < 50 m) features, including leads and ridges. The conditions leading to sea ice fracture are frequently studied in the context of a uniform ice sheet. Natural sea ice, however, is highly heterogeneous and riddled with flaws. Failure occurs primarily as brittle fracture localized in space and time where stresses, and strain rates, locally exceed failure criteria. Here we seek to better understand the mechanical deformation and fracture of sea ice under such typical field conditions. In particular, we aim to characterize how forces propagate across an approximately 1 km^2 heterogeneous domain by observing the stress-strain field in an ice floe at resolutions required to capture pre-fracture elastic strains. The combination of instruments deployed allow a detailed view of the formation, propagation, parting, and subsequent shearing of a fracture in natural sea ice, providing field evidence of modes of failure in compressive shear. The relatively low change in stress observed within meters of the fracture location highlights the need for further research into disparities in sea ice strength measurements at laboratory and field scales. The ability of this system to capture strain concentration zones and to detect initial fracture hours prior to lead formation indicates the potential for predicting areas at high risk for fracture in an on-ice operational setting.