Dike swarms are ubiquitous on terrestrial planets and represent the frozen remnants of magma transport networks. However, spatial complexity, protracted emplacement history, and uneven surface exposure typically make it difficult to quantify patterns in dike swarms on different scales. In this study, we address this challenge using the Hough Transform to objectively link dissected dike segments and analyze multiscale spatial structure in dike swarms. We apply this method to swarms of three scales: the Spanish Peaks, USA; the Columbia River Flood Basalt Group (CRBG), USA; the Deccan Traps Flood Basalts, India. First, we cluster dike segments in Hough Transform space, recognizing prevalent linearly aligned structures that represent single dikes or dike packets, with lengths up to $10-30x$ the mapped mean segment length. Second, we identify colinear and radial dike segment mesoscale structures within each data set, using the Hough Transform to segment swarms into constituent spatial patterns. We show that for both the CRBG and Deccan Traps, a single radial swarm does not well characterize the data. Instead, multiple and sometimes overlapping mesoscale linear and radial features are prevalent. This suggests a time-evolving transport network where structural inheritance of dike pathways over an extended time is likely common, but large-scale reorganizations of the plumbing system that imply state shifts in crustal stresses or mantle melt supply also occur. We expect that the Hough Transform may find useful applications in a variety of geologic settings where many quasi-linear features, at any scale, are superimposed spatially.

Very-long-period (VLP) volcano seismicity often represents subsurface magma movement, and thus provides insight into magma system geometry and magma properties. We develop a fully automated signal processing workflow using wavelet transforms to detect and assess period, decay rate, and ground motions of resonant VLP signals. We then generate and analyze a catalog of VLP seismicity over the 2008-2018 open-vent summit eruptive episode at Kilauea Volcano, Hawaii USA. VLP seismicity occurred throughout this eruption that involved a persistent lava-lake, multiple intrusions and rift zone eruptions, and a climactic caldera collapse. We characterize trends in two dominant magma resonances: the fundamental eigenmode of the shallow magma system is a vertical oscillation of the magma column in the conduit and lava-lake, and higher frequency eigenmodes largely consist of lateral lava-lake sloshing. VLP seismicity was mainly triggered by lava-lake surface perturbations, and less commonly from depth. Variation in periods and quality factors occurred on timescales from hours to years. VLP seismicity exhibited varying correlations over time with other datasets such as ground tilt, SO2 emissions, and lava-lake elevation. Variation in VLP properties also occurred over days to months preceding and following intrusions and rift zone eruptions. Changes in VLP ground motions over various timescales indicate evolution of shallow magma system geometry, which contributed to the variation in resonance. However much of the variation on timescales less than months is likely from changing magma density and viscosity, reflecting a variable shallow magmatic outgassing and convective regime within the open conduit over the ten year eruption.

Long-duration, continuous geodetic timeseries suggest that volcanoes exhibit a wide range of deformation patterns that vary between episodes of unrest. Viscoelastic deformation around crustal magma storage zones is an expected contributor to such observations, but is challenging to characterize robustly. Here we present an analytic approach for modeling crustal deformation around magma reservoirs that highlights frequency-domain signatures of viscoelastic response for temperature-dependent crustal rheology. We develop a transfer function that links frequency spectra of chamber pressure to surface displacement, finding that properties of the magmatic system are encoded at periods where geodetic observations are routinely made. Inhomogeneous viscoelastic response is characterized by a frequency-dependent elastic-viscous transition around the reservoir. We explore the consequences of this frequency dependence by examining broadband forcing consisting of multiple impulsive pressurization episodes, and identify a history dependence of volcano deformation in which past activity influences the stress state and surface deformation of future episodes.

Determining the spatial relations between volcanic edifices and their underlying magma storage zones is fundamental for characterizing long-term evolution and short-term unrest. We compile centroid locations of upper crustal magma reservoirs at 56 arc volcanoes inferred from seismic, magnetotelluric, and geodetic studies. We show that magma reservoirs are often horizontally offset from their associated volcanic edifices by multiple kilometers, and the degree of offset broadly scales with reservoir depth. Approximately 20% of inferred magma reservoir centroids occur outside of the overlying volcano’s mean radius. Furthermore, reservoir offset is inversely correlated with edifice size. Taking edifice volume as a proxy for long-term magmatic flux, we suggest that high flux or prolonged magmatism leads to more centralized magma storage beneath arc volcanoes by overprinting upper crustal heterogeneities that would otherwise affect magma ascent. Edifice volumes therefore reflect the spatial distribution of underlying magma storage, which could help guide monitoring strategies at volcanoes.