The physical and chemical processes that have operated in a fault zone are archived in fault rocks which are being studied with a variety of techniques and approaches. Iron-bearing (magnetic) minerals are sensitive to strain magnitude, temperature and presence of fluids in fault zones, hence magnetic properties convey information on faulting processes. Here, we demonstrate that magnetic analysis could unveils microscopic processes operating in the fault zones such as strain accumulation (state), frictional heating, and fluid percolation that are otherwise difficult to constrain, hence this analysis informs on earthquake dynamics. This makes magnetic property to be ‘strain indicator’, ‘geothermometer’, and ‘fluid tracer’ in fault zones, which are expected to place our understanding of the microphysics of faulting on a much stronger footing.