Microscopic Evolution of Laboratory Volcanic Hybrid Earthquakes

Abstract

Characterizing the interaction between fluids and microscopic defects is one of the long-standing challenges in understanding a broad range of cracking processes, in part because they are so difficult to study experimentally. We address this issue by reexamining records of emitted acoustic phonon events during rock mechanics experiments under wet and dry conditions. The frequency spectrum of these events provides direct information regarding the state of the system. Such events are typically subdivided into high frequency (HF) and low frequency (LF) events, whereas intermediate “Hybrid” events, have HF onsets followed by LF ringing. At a larger scale in volcanic terranes, hybrid events are used empirically to predict eruptions, but their ambiguous physical origin limits their diagnostic use. By studying acoustic phonon emissions from individual microcracking events we show that the onset of a secondary instability–related to the transition from HF to LF–occurs during the fast equilibration phase of the system, leading to sudden increase of fluid pressure in the process zone. As a result of this squeezing process, a secondary instability akin to the LF event occurs. This mechanism is consistent with observations of hybrid earthquakes.

A new numerical method for evaluating the variation of casing inner diameter after strike‐slip fault sliding during multistage fracturing in shale gas wells

“…[22][23][24] According to the measurement results of microseism, fault radius could be expressed using the following equation where r 0 represents the radius of the slip fault, m; M w represents the microseismic moment magnitude, dimensionless; Δσ represents the stress drop, Pa. [22][23][24] According to the measurement results of microseism, fault radius could be expressed using the following equation where r 0 represents the radius of the slip fault, m; M w represents the microseismic moment magnitude, dimensionless; Δσ represents the stress drop, Pa.…”

“…Once the fault slid, there were increasing occurrences of seismicity associated with fault activation during multistage fracturing. [22][23][24] According to the measurement results of microseism, fault radius could be expressed using the following equation where r 0 represents the radius of the slip fault, m; M w represents the microseismic moment magnitude, dimensionless; Δσ represents the stress drop, Pa. Both M w and Δσ can be measured based on the microseismic survey.…”