Influence ofin situstress variations on acoustic emissions: a numerical study
32
Citation
45
Reference
10
Related Paper
Citation Trend
Abstract:
The study of acoustic emissions (AEs) is of paramount importance to understand rock deformation processes. AE recorded during laboratory experiments mimics, in a controlled geometry and environment, natural and induced seismicity. However, these experiments are destructive, time consuming and require a significant amount of resources. Lately, significant progresses have been made in numerical simulations of rock failure processes, providing detailed insights into AE. We utilized the 2-D combined finite-discrete element method to simulate the deformation of Stanstead Granite under varying confining pressure (Pc) and demonstrated that the increase of confining pressure, Pc, (i) shifts failures from tensile towards shear dominated and (ii) enhance the macroscopic ductility. We quantitatively describe the AE activity associated with the fracturing process by assessing the spatial fractal dimension (D-value), the temporal distribution (AE rate) and the slope of the frequency–magnitude distribution (b-value). Based on the evaluation of D-value and AE rate, we defined two distinct deformation phases: Phase I and Phase II. The influence of Pc on the spatial distribution of AE varies according to the deformation phase: for increasing Pc, D-value decreases and increases during Phases I and II, respectively. In addition, b-value decreases with increasing Pc during the entire experiment. Our numerical results show for the first time that variations of D- and b-values as a function of in situ stress can be simulated using the combined finite-discrete element approach. We demonstrate that the examination of seismicity should be carried out carefully, taking into consideration the deformation phase and in situ stress conditions.Keywords:
Acoustic Emission
Overburden pressure
Ductility (Earth science)
The relationship between seismicity enhancement parameter W 1 and corresponding seismicity parameters, and their variation before some earthquakes about M S6.0 are analysed in this paper.The results show that there are three forms on enhancement of seismicity before moderate or strong earthquakes,the first is the enhancement on magnitude,the second is the temporal and spatial cluster of seismicity,the third appears as the first and the second forms concurrently.The variation of dynamic pattern of W 1 value before some earthquakes about M S6.0 shows that seismogenic process is an evolution process of interaction of many stress concentration zones.
Variation (astronomy)
Cite
Citations (0)
Cite
Citations (296)
In most cases of reservoir-induced seismicity, seismicity follows the impoundment, large lake-level changes, or filling at a later time above the highest water level achieved until then. We classify this as initial seismicity. This "initial seismicity" is ascribable to the coupled poroelastic response of the reservoir to initial filling or water level changes. It is characterized by an increase in seismicity above preimpoundment levels, large event(s), general stabilization and (usually) a lack of seismicity beneath the deepest part of the reservoir, widespread seismicity on the periphery, migrating outwards in one or more directions. With time, there is a decrease in both the number and magnitudes of earthquakes, with the seismicity returning to preimpoundment levels. However, after several years some reservoirs continue to be active; whereas, there is no seismicity at others. Preliminary results of two-dimensional (similar to those by Roeloffs, 1988) calculations suggest that, this "protracted seismicity" depends on the frequency and amplitude of lake-level changes, reservoir dimensions and hydromechanical properties of the substratum. Strength changes show delays with respect to lake-level changes. Longer period water level changes (~ 1 year) are more likely to cause deeper and larger earthquakes than short period water level changes. Earthquakes occur at reservoirs where the lake-level changes are comparable or a large fraction of the least depth of water. The seismicity is likely to be more widespread and deeper for a larger reservoir than for a smaller one. The induced seismicity is observed both beneath the deepest part of the reservoir and in the surrounding areas. The location of the seismicity is governed by the nature of faulting below and near the reservoir.
Cite
Citations (43)
Positive correlation
Negative correlation
Cite
Citations (8)