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Ground deformation in volcanic areas induced by geothermal fluid circulation can reveal useful information about the dynamical processes occurring in the subsurface hydrothermal system. In the present work, we investigate tiltmeter time-series recorded at Aso Volcano during 2011–2016, a time interval during which different phases of volcanic activity occurred. We performed polarization analysis of the data and identified peculiar long-lasting (hours) transients, defined as Very-Long-period Tilt Pulses. The transients were further characterized in terms of waveform cross-correlation, particle tilt pattern, energy, and time distributions. The analyses indicate that such signals, which appear like deflation–inflation (DI) events, are associated with a Poissonian process whose underlying dynamics evolves over time always driven by a Poissonian mechanism. The obtained results have been interpreted in light of the available geophysical, geochemical and volcanological information. In this framework, the Very-Long-period Tilt Pulses may be ascribed to the depressurization/pressurization of the shallow hydrothermal system according to a fault-valve mechanism, which was active with different efficiency throughout eruptive and inter-eruptive phases. [ABSTRACT FROM AUTHOR]

One of the strategies to detect the precursors of an eruption is to define the background dynamical state of a volcano for a prompt recognition of deviations from the basic condition. Mt. Vesuvius (Italy), currently in a quiescent state, is one of the most monitored volcanoes in the world, inciting multidisciplinary advanced studies. Hence an understanding of the links among the different monitored parameters is mandatory. In recent decades the joint analyses of ground tilt and seismicity have added to the understanding of the volcano's activity. In this paper, we outline the first steps towards a comprehension of the link between Mt. Vesuvius earthquakes and co-seismic ground tilt, after excluding the contribution of other external forces acting on the ground, such as tides, landslides or exceptional meteorological phenomena. We used the seismicity with a duration magnitude ≥ 2.0 recorded at Mt. Vesuvius in the period 2018–2020 to estimate the source parameters and to calculate the associated static displacement. Then, we compared the ground inclination retrieved from the estimated seismic deformation with the long-term ground motion trend measured by tiltmeters. We found that in most cases the two vectors have a comparable size and direction. [ABSTRACT FROM AUTHOR]

This work is devoted to the analysis of the background seismic noise acquired at the volcanoes (Campi Flegrei caldera, Ischia island, and Vesuvius) belonging to the Neapolitan volcanic district (Italy), and at the Colima volcano (Mexico). Continuous seismic acquisition is a complex mixture of volcanic transients and persistent volcanic and/or hydrothermal tremor, anthropogenic/ambient noise, oceanic loading, and meteo-marine contributions. The analysis of the background noise in a stationary volcanic phase could facilitate the identification of relevant waveforms often masked by microseisms and ambient noise. To address this issue, our approach proposes a machine learning (ML) modeling to recognize the "fingerprint" of a specific volcano by analyzing the background seismic noise from the continuous seismic acquisition. Specifically, two ML models, namely multi-layer perceptrons and convolutional neural network were trained to recognize one volcano from another based on the acquisition noise. Experimental results demonstrate the effectiveness of the two models in recognizing the noisy background signal, with promising performance in terms of accuracy, precision, recall, and F1 score. These results suggest that persistent volcanic signals share the same source information, as well as transient events, revealing a common generation mechanism but in different regimes. Moreover, assessing the dynamic state of a volcano through its background noise and promptly identifying any anomalies, which may indicate a change in its dynamics, can be a practical tool for real-time monitoring. [ABSTRACT FROM AUTHOR]

We study the time changes of (1) the b-value of the Gutenberg-Richter distribution, (2) the inverse coda Q(Qc-1), and (3) the shear-wave splitting parameters (i.e., the time delay Td between qS1 and qS2 phases and the polarization direction of the qS1 wave) for small-magnitude volcano-tectonic earthquakes of Mt. Vesuvius, Italy. We used for (1) the seismic catalog of Mt. Vesuvius seismicity starting from January 1994, for (2) a selected (on the basis of the best signal-to-noise ratio) set of data with hypocentral distances smaller than 4 km recorded at station BKE (analogical) with a 1-Hz vertical seismometer during the period from January 1994 until the present, and for (3) a set of data recorded at two digital, high dynamical range, portable short-period seismic stations. These stations (BKE and BKN) were in operation in two periods, BKE (digital) from January 1999 to the middle of 2000 and BKN from January 1999 to the end of 1999; the hypocentral distances were not greater than 4 km. We found evidence of time changes of Qc-1 measured at high frequency (6, 12, and 18 Hz). The changes seem to be correlated with the occurrence of two swarms with largest magnitudes of 3.4 and 3.6, respectively in April 1996 and October 1999. The earthquake with the largest magnitude in the second swarm appears to be the largest event since the latest eruption in 1944. An increase in Qc-1starts after the occurrence of both swarms, reaching a maximum after more than 1 yr for the first swarm and after 6 months for the second swarm. These two changes were not accompained by any corresponding variation of the b-value, which shows an almost constant (inside the statistical uncertainty) pattern. The last swarm (M 3.6) was precedeed by an increase of Td at both stations, indicating a possible change of the stress state before the M 3.6 earthquake. The qS1... [ABSTRACT FROM AUTHOR]

In the present paper, we analyse ground tilt and seismicity at Campi Flegrei caldera and Ischia Island, two volcanic areas located in the south of Italy. These areas have been well studied for many years from a petrological, volcanological and geophysical view point. Moreover, due to the high seismic and volcanic risk for the populations living there, they are continuously monitored by networks of geophysical and geochemical sensors. We summarize the most important results that we obtained so far, concerning the observations of relationships between seismic activity and ground tilt anomalies, focusing on the time interval 2015–2018. First, we present a detailed description of the tiltmeter and seismic networks in both the investigated areas, as well as their development and improvement over time that has enabled high quality data collection. From the joint analysis of the seismic and borehole tiltmeter signals, we often notice concurrence between tilt pattern variations and the occurrence of seismicity. Moreover, the major tilt anomalies appear to be linked with the rate and energy of volcano-tectonic earthquakes, as well as with exogenous phenomena like solid Earth tides and hydrological cycles. The analysis that we present has potential applicability to other volcanic systems. Our findings show how the joint use tilt and seismic data can contribute to better understanding of the dynamics of volcanoes. [ABSTRACT FROM AUTHOR]

We analyse and compare volcano-tectonic seismicity, rainfall, atmospheric pressure, ground deformation and Earth tide time series at the Campi Flegrei caldera (CFc) in the time interval 2005-2016, looking for possible tidal and hydrological triggers of hydrothermal and seismic activity. By applying statistical analysis, we show that the occurrence of clustered seismicity at the CFc has a cyclic behaviour on several time scales, from semidiurnal and diurnal to longer periods, such as fortnightly, monthly, semiannual and annual. The medium and long-period time scales match those of the main lunar and solar tidal constituents, while the exactly 24-h and 12-h periodicities can be ascribed not only to the Earth tides but also to other effects such as atmospheric pressure and temperature variations. In addition, a clear dependence on rainfall arises from the analysis of the hydrological parameters, indicating a strong seasonal periodicity along the entire observational interval, with the most numerous and energetic seismic swarm occurring in the wet season.We interpreted these observations in terms of a model linking magmatic degassing, ground deformation and seismicity. The proposed model considers the magmatic-hydrothermal fluid circulation system as a cascade hydraulic circuit, where in/out fluid flow and pressure condition of each segment are regulated by those of the contiguous ones. Our results suggest that volcano-tectonic seismicity at CFc is driven by both variations in the deep magmatic feeding system and exogenous phenomena, as rainfall or global inflation/deflation cycles of the Earth' s crust, controlled by the lunisolar interaction. Consequently, the role of exogenous triggers (combined with endogenous processes) in the evolution of the recent dynamics should be properly considered in the elaboration of volcanic risk scenarios. [ABSTRACT FROM AUTHOR]

Long period volcanic tremors (LPTs), typically termed as VLP, have been widely observed in many volcanic systems around the world. LPTs in different volcanic settings are often repetitive, suggesting a nondestructive source and providing critical insights into the fluid dynamic processes operating inside a volcanic system. Recently, a deep triggering source of LPT has also been discovered, located between the LPT source and the magma chamber. These diverse and rich signals not only help monitor the state of shallow volcanic conduit and its link to upcoming eruptions. it also helps understand causal triggering of LPT and potentially intra-crustal transport of magma. Given diverse and rich signals within the Aso volcanic system, we further explore other possible sources in the tidal period. We analysed continuous data recorded at two borehole tiltmeters installed at Aso volcano, during the period of 2011-2016. We first perform a polarisation analysis of the ground tilt, filtering in the frequency bands matching the medium-long period tidal constituents, Mm, Mf and S1. The results evidence a well-defined direction of the tilting plane at both sites, with minor fluctuations occurring in 2012 and 2014. Moreover, we investigated the tilt time series the 1-8 hour band. There is a clear variation in azimuth orientation in at least one of the two tiltmeters and these azimuthal variations occur roughly from September 2013 at least until November 2014. In the meantime, LPTs were strong and more active, ash eruption occurred at the end of August 2014, followed by a major Strombolian eruption episode starting at the end of November 2014. In this time interval between September 2013 and November 2014, we further discovered a sequence of nearly monochromatic signals, with repetitive waveforms, a typical period of about 2 hours and a duration of about 9 hours. We extracted these signals and will compare their timing against the LPT catalog we constructed previously. Moreover, we will perform waveform correlation in order to quantify the degree of similarity among these monochromatic signals. Finally, we will attempt to reconcile all these observations in terms of the volcano dynamics and of its different eruptive styles during the 2011-2016 eruption cycle. [ABSTRACT FROM AUTHOR]