Imaging Localized Slip‐Induced Frictional Heating During Laboratory Earthquakes Using Magnetic Microscopy

Slip‐induced heating is crucial for understanding fault mechanics and energy partitioning during earthquakes. The strongest heating occurs in a thin, millimeter to sub‐millimeter‐scale zone, which poses a challenge for existing geothermometers because they lack spatial resolution or are limited to specific rock compositions. Here, we utilize the recently developed quantum diamond microscope (QDM) to resolve thermal demagnetization at micrometer resolution around experimentally produced slip zones, thereby quantifying the near‐field slip‐induced temperature excursion. This new technique also enables us to observe ∼300 μm‐scale along‐fault heterogeneities in heating intensity, highlighting the role of localized stress and deformation in guiding frictional evolution. A simple 1‐dimensional heat diffusion model can simultaneously satisfy the temperature estimates from QDM, far‐field thermocouple measurements, and microstructural observations of localized melting. This model constrains the thermal energy density during slip to be 52–65 kJ/m 2 during our laboratory earthquakes, which accounts for 52%–75% of the total energy budget. We also estimate that the average friction coefficient during rapid slip is 0.2–0.3, suggesting significant weakening during slip. Our results provide new insights into the role of localized heating during earthquake‐like failure and illuminate the role of thermal weakening mechanisms at pressures corresponding to the base of the seismogenic crust.