[S-VC28] International Volcanology

[SVC28-09] Resonances in a fluid-filled crack of arbitrary shape and its application to very long period (VLP) signals at Mayotte submarine volcano

*Junjun Peng¹, Chao Liang¹, Jean-Paul Ampuero², Nathan Shauer³, Kaoshan Dai¹ (1.Institute for Disaster Management and Reconstruction, Sichuan University, Chengdu, China, 2.Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, IRD, Géoazur, Valbonne, France, 3.LabMeC-FECAU-Universidade Estadual de Campinas, 13083-841 Campinas-SP, Brazil)

Keywords:Fluid-filled cracks, Crack wave, Boundary element method, Finite volume method, Resonant frequency, VLP signals of Mayotte submarine volcano

Fluid-filled cracks sustaining a slow guided wave (Krauklis wave or crack wave) are a widely used model for interpreting very long period (VLP) seismic signals at active volcanoes. However, previous works focus on analytical developments along an infinite crack or a simple rectangular geometry due to limitations of the finite difference method or spectral method. One notable exception is by Shauer et al. (2021) who used a generalized finite element method (GFEM) to model fluid-filled cracks with general shapes, yet at a costly expense of discretizing the 3D solid volume. In this work, we develop a simple method for modeling resonances in an arbitrarily shaped fluid-filled crack and apply it to explain the VLP signals at Mayotte submarine volcano. By coupling boundary elements with triangular dislocation and a finite volume method, we successfully handle complex geometries while achieving substantial computational efficiency. Through eigenvalue analysis, we directly extract resonant modes in the frequency domain, eliminating errors from both time discretization and spectral analysis of time domain simulation data. The resulting resonant frequencies match well those computed by the GFEM solver of Shauer et al. (2021) for both rectangular and elliptical shapes, demonstrating the validity of our approach. We also show that the solid inertia has a negligible effect on crack wave resonances at low frequencies, justifying the quasi-static elastic approximation for the solid. We then systematically analyze the resonant modes of rectangular and elliptical cracks and quantify the effect of aspect ratio and curvature. Finally, we compute resonant modes of a crack with a complex geometry and successfully explain the characteristic ratio between the fundamental mode and the first higher mode in the VLP seismic data from the Mayotte submarine volcano. Our work not only reveals the effect of complex geometry on crack wave resonances but also demonstrates the capability to illuminate the subsurface plumbing system of active volcanoes. The model developed here is readily applicable to crack wave resonances in other geological settings, such as glacier hydrology and hydrocarbon reservoirs.