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Using geodetic methods, significant static ground deformation has been observed for many large natural earthquakes. Some of the largest earthquakes induced by hydraulic-fracturing operations have been observed in the Western Canada Sedimentary Basin; however, because of the size and depths of these events, the associated static ground deformations have not yet been observed using traditional geodetic techniques. A seismic processing technique, developed for small volcano-seismic events, has the potential to resolve micrometer-scale static displacements using broadband seismic data. In this study, we test this processing method using vertical component broadband recordings of an Mw 4.1 event acquired at four nearby broadband seismometers. Estimated static displacements at the four stations are compared with the theoretical surface displacement field for a dislocation on a finite rectangular source within a homogeneous, elastic half-space. The theoretical displacements have the same polarities as the measured displacements across the seismic network and have similar amplitudes for three of the four stations. However, one station yielded unstable results, which shows that care must be taken when using this method. These results suggest that this processing method has potential for obtaining surface deformation for small to moderate-sized earthquakes using broadband data. [ABSTRACT FROM AUTHOR]

Seismic swarms are defined as an increase in seismicity that does not show a clear mainshock-aftershock sequence. Typically, swarms are primarily associated with either fluid migration or slow earthquakes (aseismic slip). In this study, we analyze a swarm induced by hydraulic fracturing (HF) that persisted for an unusually long duration of more than 10 months. Swarms ascribed to fluid injection are usually characterized by an expanding seismicity front; in this case, however, characteristics such as a relatively steady seismicity rate over time and lack of hypocenter migration cannot be readily explained by a fluid-diffusion model. Here, we show that a different model for HF-induced seismicity, wherein an unstable region of a fault is loaded by proximal, pore-pressure-driven aseismic slip, better explains our observations. According to this model, the steady seismicity rate can be explained by a steady slip velocity, while the spatial stationarity of the event distribution is due to lateral confinement of the creeping region of the fault with increased pore pressure. Our results may have important implications for other induced or natural seismic swarms, which could be similarly explained by aseismic loading of asperities driven by fluid overpressure rather than the often-attributed fluid-migration model. [ABSTRACT FROM AUTHOR]