Laboratory Inspirational Information on the "Burst-Like" and "Swarm-Like" Energy Releases from Anthropogenic Rock Fracture Processes
Authors: Xiong Q. , Lin Q. , Gao Y. , Hampton J. C. 
Published: September 2022

ABSTRACT:
Laboratory experimental tests can provide inspirational information for geologists and/or geophysicists to understand field-scale phenomena and processes. Field-scale anthropogenic seismicity catalogs are usually dominated by swarm-like features, while the natural seismicity of structural faults (i.e., the San Andreas fault) clearly exhibits the co-existence of both swarm-like and burst-like energy releases. This paper compares the energy release features from the laboratory anthropogenic (i.e., loading induced) rock fracture processes from different types of laboratory tests. We use a comparatively objective model to inspect the topology structure of the laboratory energy releases, i.e., an acoustic emission (AE) network, and to inspect/characterize the energy release features. The model we have used demands only the energy releases obey the scaling-law. Thus scale-invariance on these energy releases has been inspected and verified. By combining the known different laboratory settings with their consequentially induced different energy release features, we postulate an inspirational understanding on the mechanisms that distinguish the burst-like and swarm-like energy releases. The spatial discontinuity may be one influential factor for differentiating the catalog into dominant swarm-like or mixed burst- and swarm-like behavior. Further investigations on identifying and quantifying other possible influential factors that differentiate the catalogs into different types are warranted.

1. INTRODUCTION
Induced seismicity from hydraulic fracturing (Kozłowska et al., 2018; Skoumal et al., 2015b, 2018a; Skoumal et al., 2018b) or waste water disposal (Skoumal et al., 2020a; Skoumal et al., 2015a; Skoumal et al., 2016; Skoumal et al., 2020b) is dominated by swarm-like features. This swarm-like feature describes the energy releases of the stressed underground rock mass as having spatial-temporal affinity, for instance, characterized by narrow aftershock/seismic-active zones (Karimi and Davidsen, 2021). Natural seismicity, on the contrary, display clearly different mixed burst-like and swarm-like features (Zaliapin and Ben-Zion, 2013a, b), with some regions of seismicity reported as more swarm-like or more burst-like (Brodsky et al., 1998; Sturtevant et al., 1996; Zaliapin and Ben-Zion, 2013b). Multiple mechanisms can cause the different regional observations of the burst-like or the swarm-like seismicity features, e.g., the brittle and creeping features due to lithology differences, geothermal flows (Zaliapin and Ben-Zion, 2013b), or the "rectified diffusion" process because of the bubble release from the porous fluid (Sturtevant et al., 1996), etc. A further comprehensive and quantitative decoupling of the possible mechanisms involved is challenging for field-scale studies. This is partially due to the limited accessibility to various types of in-situ measurements and the limited temporal coverage of scientific observations on the seismic activity.