Abstract
Long-period events (LPs) are observed in active volcanoes, hydrothermal
systems, and hydraulic fracturing. The prevailing model for LP events
suggests that they result from pressure disturbances in fluid-filled
cracks that generate slow, dispersive waves known as Krauklis waves.
These waves oscillate within the crack, causing it to act as a seismic
resonator whose far-field radiations are known as LP events. Since LP
events are generated from fluid-filled cracks, they have been used to
analyze fluid transport and fracturing in geological settings.
Additionally, they are deemed precursors to volcanic eruptions. However,
other mechanisms have been proposed to explain LP seismicity. Thus, a
robust interpretation of LP events requires understanding all parameters
contributing to LP seismicity. To achieve this, for the first time, we
have developed a physical model to investigate LP seismicity under
controlled-source conditions. The physical model consists of a 30 cm ×
15 cm × 0.2 cm crack embedded within a concrete slab with dimensions of
3 m × 3 m × 0.24 m. Using this apparatus, we extensively investigate
fundamental factors affecting LP signals, including crack stiffness,
fluid viscosity, radiation patterns, and triggering location. Our
findings are consistent with the theoretical model for Krauklis waves
within a fluid-filled crack. For instance, a reduction in stiffness
leads to an increase in resonance frequency, whereas an increase in
fluid viscosity results in a decrease in resonance frequency. Thus, this
physical model can offer new horizons in understanding LP seismicity and
bridge the gap between theoretical models and observed LP signals.