← Back to Sessions

Laboratory Observation of Large Fluid Pressure Amplification in a Fluid-Filled Fracture

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip [Poster]

Type: Poster

Date: 4/20/2021

Presentation Time: 04:15 PM Pacific

Description: 

It is a well-established observational phenomenon that earthquakes can be triggered by a weak-amplitude, long-period seismic waves in the geothermal and volcanic regions. The underlying mechanism, in particular, the frequency dependency and the affinity to fluids, have not been well-understood yet. Zheng (2018) found a transient pressure surge (PS) phenomenon in numerical modeling that when a seismic wave interacts with a fluid-filled fracture, the fluid pressure inside the fracture could be amplified by 2-3 orders of magnitude compared to the incident wave pressure. The PS effect both depends on the incident wave frequency and the participation of fluid. It is a competitive candidate for the underlying physical mechanism in triggering.

Here we report results from laboratory experiments about the PS effect in the frequency range of 10’s Hz. Because the PS effect happens in low frequencies. We developed a new low-frequency underwater experiment platform, including a low-frequency acoustic source (Xfrac-S), a new hydrophone (Xfrac-H) of small dimensions placed inside the thin fracture.

By adjusting the fracture aperture from 0.2mm to 9.2mm and sweeping the frequency from 12 Hz to 70Hz, we find that the fluid-pressure of the wave recorded inside the fractures can be amplified up to 25 times larger than the incident wave pressure. The amplification depends on fracture geometry and frequency.

This observation may provide a plausible explanation for both dynamic earthquake triggering because the pressure surge observed here can reduce the normal confining pressure across the fracture interfaces to trigger shear slip for earthquakes. The transient pressure surge can activate local fluid flow due to the pressure gradient. It may also be the underlying mechanism for permeability changes induced by passing seismic waves. Lastly, PS may also find new uses in induced seismicity, subsurface flow management in conventional/unconventional/geothermal reservoirs, and novel subsurface imaging.

Presenting Author: Yuesu Jin

Student Presenter: Yes

Authors