Laboratory Evidence of Transient Pressure Surge in a Fluid-Filled Fracture as a Potential Driver of Remote Dynamic Earthquake Triggering

Yuesu Jin,Nikolay Dyaur,Yingcai Zheng

doi:10.1785/0320210015

Yuesu Jin, Nikolay Dyaur + Show 1 more

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https://doi.org/10.1785/0320210015

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Abstract

Abstract Seismic waves carrying tiny perturbing stresses can trigger earthquakes in geothermal and volcanic regions. The underlying cause of this dynamic triggering is still not well understood. One leading hypothesis is that a sudden increase in the fluid-pore pressure in the fault zone is involved, but the exact physical mechanism is unclear. Here, we report experimental evidence in which a fluid-filled fracture was shown to be able to amplify the pressure of an incoming seismic wave. We built miniature pressure sensors and directly placed them inside a thin fluid-filled fracture to measure the fluid pressure during wave propagation. By varying the fracture aperture from 0.2 to 9.2 mm and sweeping the frequency from 12 to 70 Hz, we observed in the lab that the fluid pressure in the fracture could be amplified up to 25.2 times compared with the incident-wave amplitude. Because an increase of the fluid pressure in a fault can reduce the effective normal stress to allow the fault to slide, our observed transient pressure surge phenomenon may provide the mechanism for earthquake dynamic triggering.

Highlights

Earthquakes can be triggered by passing seismic waves—a phenomenon known as dynamic triggering
We first show time-domain waveforms recorded by P1 and H1–H5 (Fig. 4) at two sinusoidal source frequencies, 35 and 29 Hz, for a fracture aperture of 0.95 mm
We have demonstrated in the lab that a fluid-filled fracture can cause localized transient pressure amplification, which provides a plausible explanation for the dynamic earthquake triggering by the passage of seismic waves

Summary

Introduction

Earthquakes can be triggered by passing seismic waves—a phenomenon known as dynamic triggering. The stress amplitudes of the passing waves are very low (on the order of kPa). The triggering thresholds for these triggered events seem to be more sensitive to long-period incident waves than short-period waves of comparable amplitudes (Brodsky and Prejean, 2005; Hill and Prejean, 2015). The first one is the critical state hypothesis (e.g., Zoback and Zoback, 2002). It says that the crust is close to rupturing, and any stress perturbation, as small as the one imposed by a traveling seismic wave, could cause failures

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