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A Long‐Lived Swarm of Hydraulic Fracturing‐Induced Seismicity Provides Evidence for Aseismic Slip
Bulletin of the Seismological Society of America ( IF 3 ) Pub Date : 2020-10-01 , DOI: 10.1785/0120200107
Thomas S. Eyre 1 , Megan Zecevic 1 , Rebecca O. Salvage 1 , David W. Eaton 1
Affiliation  

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.

中文翻译:

水力压裂诱发地震的长寿群为抗震性提供了证据

地震群的定义是地震活动性的增加,并没有显示清晰的主震-余震序列。通常,群主要与流体迁移或缓慢地震(地震滑动)有关。在这项研究中,我们分析了由水力压裂(HF)引起的群体,该群体持续异常长的时间超过10个月。归因于流体注入的群通常以扩展的地震活动性为特征。然而,在这种情况下,流体扩散模型无法轻易解释诸如随时间推移相对稳定的地震活动率以及缺乏震源迁移等特征。在这里,我们显示了HF诱发地震活动的不同模型,其中断层的不稳定区域由近端孔隙压力驱动的抗震滑动加载,更好地解释了我们的观察结果。根据这个模型,稳定的地震活动率可以用稳定的滑动速度来解释,而事件分布的空间平稳性是由于断层的蠕变区域随孔隙压力的增加而受到侧向限制。我们的结果可能对其他诱发或自然地震群具有重要意义,这可以用流体超压而不是通常归因于流体迁移模型驱动的粗糙体的抗震荷载类似地解释。
更新日期:2020-09-25
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