A new approach to monitoring stochastic features of earthquake series was applied to track the preparatory process of the 2017 Tehuantepec, Mexico, Mw8.4 earthquake. The seismicity was parameterized by elapsed times and epicentral distances from the directly preceding earthquakes and by earthquake magnitudes. The transformation to equivalent dimensions ensured the comparability of these parameters. We were calculating the average distance between earthquakes in the transformed parameter space in moving in time data windows, each consisting of 100 events. The average distance exhibited a consistent upward trend from ten to two years before the main shock. Then, it declined until the main shock. This precursory up-down signal was highly significant statistically. We showed that the detected time changes of the average distance resulted from the evolution of the earthquake clustering in the considered parameters' equivalent dimensions space.

Deep underground water injections induce seismicity. When the seismic fractures coalesce into far-reaching pathways for fluid migration, the migrating fluid may reach pre-existing faults, and by decreasing fault strength, can trigger major seismic events. We assume that the potential for building such pathways depends on closeness of hypocenters, similarity of fracture planes orientations, and closeness of radii taking off from the injection point, on which events locate. We define this potential as the average distance between seismic events in the space of parameters quantifying the above conditions. We show that in the studied case from The Geysers geothermal field, this potential is highly correlated with injection rate. When the overall level of injection rate is high, the higher the injection rate, the more the potential for building far-reaching pathways for fluid migration is reduced.