Abstract

Understanding the relationship between earthquake rupture processes and injection locations can shed lights on the underlying triggering mechanisms of induced seismicity. Rupture directivity, in particular, has strong effects on the resulting ground motions. Here, we constrain rupture directivity of four major induced earthquakes (Mw5.0) in the central United States that occurred between 2011 and 2016. We utilize the rich pool of broadband and strong‐motion seismic data and select smaller earthquake recordings as empirical Green’s functions (EGFs) to forward‐model the rupture directions of the target events assuming the 1D Haskell model. The typical notion is that rupture tends to propagate away from the injection site where fluid pressure is the highest. Our analysis of four target earthquakes indicates various rupture styles with respect to the location of injection wells. The 2011 Mw 5.7 Prague and 2016 Mw 5.0 Cushing earthquakes ruptured away from the injection wells, whereas the 2016 Mw 5.1 Fairview earthquake ruptured toward the injection. The 2016 Mw 5.8 Pawnee earthquake, potentially due to a downward initial rupture, shows weak to no bias of rupture directivity relative to the injection source in our analysis. In light of theoretical models of induced earthquake rupture, we find that high‐pressure injection and low initial shear stress on the fault, which are well suited to describe the Fairview region, may favor rupture toward the injection well if earthquakes are primarily induced by pore‐pressure change on the fault.

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