Simulation of LP seismic signals modeling the fluid–rock dynamic interaction

Abstract

We present an investigation on the fluid–rock dynamic interaction in a fluid-driven conduit embedded in an infinite, homogeneous elastic space. In our model, the fluid and the rock are dynamically coupled by enforcing continuity of radial velocities and tractions at the conduit wall. A pressure transient applied at the bottom of the conduit perturbs the steady flow of the incompressible viscous fluid, driving the interaction between the fluid flow and motion of the conduit's walls. The fluid motion induces an elastic response of the conduit, forcing it to oscillate radially. Our model allows connection in series of any number of fluid-filled pipe segments of different sizes simulating the geometry of volcanic conduits and an extended source mechanism, which generates long lasting oscillations. The fluid-filled conduit dynamics is governed by three ordinary, second-order, non-linear differential equations, which are solved numerically by applying a fifth-order Runge–Kutta scheme. The fluid motion and the pressure along the conduit are calculated. Far-field velocity synthetics radiated by the motion of the conduit walls and fluid flows ascending to the surface, display characteristic waveforms and frequency contents that are similar to those of long-period signals and tremor observed at active volcanoes. Our model demonstrates, from derived governing equations, that mass transport as fluid flow, generates oscillations resulting from the fluid–rock dynamic interaction, thus it is a possible mechanism to explain long-period signals and tremor.