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Abstract Foreshocks provide valuable information on the nucleation process of an upcoming large earthquake. We applied high‐resolution similar‐waveform techniques for earthquake detection, location, and source parameter estimation to understand the space‐time evolution of a foreshock sequence and its relationship to the mainshock hypocenter. The 1999M_w7.1 Hector Mine, California, earthquake was preceded by 50 foreshocks (−0.4 ≤ M ≤ 3.7) during the 20 hr before the mainshock. Foreshock activity did not accelerate leading up to the mainshock. Their locations moved north with time, rupturing adjacent areas along the fault plane with little overlap, but remained within a compact <2 km³volume. The mainshock initiated at a location where previous foreshocks had locally increased the shear stress. These observations are consistent with a triggered cascade of stress transfer, where previous foreshocks load adjacent fault patches to rupture as additional foreshocks, and eventually the mainshock. 

Understanding the behavior of Earth through the diverse fields of the solid Earth geosciences is an increasingly important task. It is made challenging by the complex, interacting, and multiscale processes needed to understand Earth’s behavior and by the inaccessibility of nearly all of Earth’s subsurface to direct observation. Substantial increases in data availability and in the increasingly realistic character of computer simulations hold promise for accelerating progress, but developing a deeper understanding based on these capabilities is itself challenging. Machine learning will play a key role in this effort. We review the state of the field and make recommendations for how progress might be broadened and accelerated.