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Seismicity at active volcanoes provides crucial constraints on the dynamics of magma systems and complex fault activation processes preceding and during an eruption. We characterize time‐dependent spectral features of volcanic earthquakes at Axial Seamount with unsupervised machine learning (ML) methods, revealing mixed frequency signals that rapidly increase in number about 15 hr before eruption onset. The events migrate along pre‐existing fissures, suggesting that they represent brittle crack opening driven by influx of magma or volatiles. These results demonstrate the power of unsupervised ML algorithms to characterize subtle changes in magmatic processes associated with eruption preparation, offering new possibilities for forecasting Axial's anticipated next eruption. This analysis is generalizable and can be employed to identify similar precursory signals at other active volcanoes. Plain Language Summary: Our research used observations of small earthquakes to understand the dynamic behaviors of magma and fault systems before and during a volcano eruption. Specifically, we used ML techniques to search for patterns in the waveforms that may inform us of their associated physical processes. At Axial Seamount, an active underwater volcano, we discovered distinct patterns in earthquake signals preceding and during the 2015 eruption. Based on event spectral patterns, we identified signals of mixed‐frequency earthquakes that rapidly increase in number about 15 hr before the eruption starts and migrate along pre‐existing eruptive fissures. The spectral pattern involves a mixture of low frequency energy following the first arrivals, which we interpret to represent opening of cracks and being filled with magma or gases. Our study demonstrates that we can use ML algorithms to detect subtle changes in volcanic signals and help us better understand the processes leading up to an eruption. This may help us in forecasting Axial's upcoming eruption and can be applied to other active volcanoes too. Key Points: Unsupervised learning separated regular earthquakes and precursory mixed frequency earthquakes (MFEs) based on different spectral patternsThe regular earthquakes have strong tidal modulation, corresponding to failures on the caldera ring faults triggered by tidal stress changesThe MFEs intensify 15 hr before eruption and migrate along pre‐existing fissures, likely associated with eruption preparation processes [ABSTRACT FROM AUTHOR]

Temporal changes in seismic velocity estimated from ambient seismic noise can be utilized to infer subsurface properties at volcanic systems. In this study, we process 7 years of continuous seismic noise at Axial Seamount and use cross‐correlation functions to calculate the relative seismic velocity changes (dv/v) beneath the caldera. We find a long‐term trend of decreasing velocity during rapid inflation, followed by slight increase in velocities as background seismicity increases and inflation rate decreases. Furthermore, we observe small short‐term increases in dv/v which coincide with short‐term deflation events. Our observations of changes in dv/v and their correlation with other geophysical data provide insights into how the top ∼1 km of the crust at Axial Seamount changes in response to subsurface magma movement and capture the transition from a period of rapid reinflation to a period where the caldera wall faults become critically stressed and must rupture to accommodate further inflation. Plain Language Summary: Changes in seismic velocity calculated from continuous background seismic signals recorded by seismometers can be used to infer subsurface properties of volcanic systems. In this study, we process 7 years of continuous seismic noise at Axial Seamount, an active submarine volcano, to calculate the relative seismic velocity changes. We find a long‐term trend of decreasing velocity during inflation of Axial Seamount, followed by mostly stable relative seismic velocity changes that correlate with an increase in earthquake rate and eventually a decrease in inflation rate. We also observe small short‐term increases in relative seismic velocity change which coincide with small short‐term deflation events. Our observations of changes in relative seismic velocity change and their correlation to other geophysical data provide insights into how the top ∼1 km of the crust changes in response to subsurface magma movement and capture a transition in the inflation pattern at Axial Seamount. Key Points: Relative seismic velocity changes at Axial Seamount show long‐term trends reflecting changes in the accommodation of inflationTransition in pattern corresponds to change from rapid inflation through uplift to slower inflation through seismic slip of locked faultsShort‐term trends in seismic velocity variation reflect changes in magma supply and pressure with brief periods of deflation events [ABSTRACT FROM AUTHOR]

ABSTRACT In April 1991, submarine volcanic eruptions initiated the formation of numerous hydrothermal vents between 9°45' and 9°52'N along the crest of the East Pacific Rise (EPR). Dramatic changes in [...]

Author(s): Yen Joe Tan (corresponding author) [1]; Maya Tolstoy [1]; Felix Waldhauser [1]; William S. D. Wilcock [2] Seafloor spreading is largely unobserved because 98 per cent of the global [...]

Antarctic blue whales produce calls are distinct from those produced by blue whales elsewhere in the world. Acoustic data are examined for the signals from two low-latitude locales, namely, the eastern tropical Pacific Ocean and the Indian Ocean, to investigate the potential winter migratory destinations of Antarctic blue whales.

Hydroacoustic data from the eastern equatorial Pacific reveal low-magnitude seismicity concentrated at the propagating tip of the Galapagos Rise in Hess Deep. The patterns of seismicity and faulting are similar to those observed in the process zone of laboratory-scale propagating tensile cracks. Because the fracture energy required for propagation scales with crack length and process zone size, it follows that ridges can propagate stably in the brittle crust without exceptional resisting forces as proposed by previous models based on linear elastic fracture mechanics., Lithosphetic rifting and mid-ocean ridge propagation are the processes by which ocean basins are formed on Earth. Ridge propagation traditionally has been studied using the linear elastic fracture mechanics (LEFM) [...]

Tidal effects on seafloor microearthquakes have been postulated, but the search has been hindered by a lack of continuous long-term data sets. Making this observation is further complicated by the need to distinguish between Earth and ocean tidal influences oil the seafloor. In the summer of 1994, a small ocean-bottom seismograph array located 402 microseismic events, over a period of two months, on the summit caidera of Axial volcano on the Juan de Fuca Ridge. Harmonic tremor was also observed on all instruments, and Earth and ocean tides were recorded on tiltmeters installed within the seismometer packages. Microearthquakes show a strong correlation with tidal lows, suggesting that faulting is occurring preferentially when ocean loading is at a minimum. The harmonic tremor, interpreted as the movement of superheated fluid in cracks, also has a tidal periodicity. Keywords: tides, earthquakes, correlations, Axial Seamount.

Seismic imaging reveals a shallow-crustal magma chamber beneath the source site of the 1993 eruption on Coaxial segment, Juan de Fuca Ridge. The magma chamber is at least 6 [km.sup.3] in volume and contains at least 0.6 [km.sup.3] of melt, enough to supply at least several eruptions of a size equal to the one in 1993. No mid-crustal connection of this magma chamber with the magmatic plumbing of nearby Axial volcano (the current expression of the Cobb-Eickelberg hotspot) is evident, confirming previous geochemical and geological studies that argued against mixing between the two. The lack of connectivity implies that magma transport through the uppermost mantle and lower crust are very highly focused into narrow ( Keywords: Axial volcano, eruption, Juan de Fuca Ridge, magma, tomography, magma chamber.

Seafloor spreading is largely unobserved because 98 per cent of the global mid-ocean-ridge system is below the ocean surface. Our understanding of the dynamic processes that control seafloor spreading is thus inferred largely from geophysical observations of spreading events on land at Afar in East Africa and Iceland1. However, these are slow-spreading centres1 influenced by mantle plumes. The roles of magma pressure and tectonic stress in the development of seafloor spreading are still unclear. Here we use seismic observations to show that the most recent eruption at the fast-spreading East Pacific Rise just North of the Equator initiated at a melt-rich segment about 5 kilometres long4. The change in static stress then promoted almost-concurrent rupturing along at least 35 kilometres of the ridge axis, where tectonic stress had built up to a critical level, triggering magma movement. The location of impulsive seismic events indicative of lava reaching the seafloor5 suggests that lava subsequently erupted from multiple isolated6,7 magma lenses (reservoir chambers) with variable magma ascent rates, mostly within 48 hours. Therefore, even at magmatically robust fast-spreading ridges, a substantial portion of the spreading may be due to tectonic stress building up to a critical level rather than magma overpressure in the underlying magma lenses. [ABSTRACT FROM AUTHOR]