Di Luccio, Francesca

Vein networks affect the hydrothermal systems of many volcanoes, and variations in their arrangement may precede hydrothermal and volcanic eruptions. However, the long-term evolution of vein networks is often unknown because data are lacking. We analyze two gypsum-filled vein networks affecting the hydrothermal field of the active Lipari volcanic Island (Italy) to reconstruct the dynamics of the hydrothermal processes. The older network (E1) consists of sub-vertical, N-S striking veins; the younger network (E2) consists of veins without a preferred strike and dip. E2 veins have larger aperture/length, fracture density, dilatancy, and finite extension than E1. The fluid overpressure of E2 is larger than that of E1 veins, whereas the hydraulic conductance is lower. The larger number of fracture intersections in E2 slows down the fluid movement, and favors fluid interference effects and pressurization. Depths of the E1 and E2 hydrothermal sources are 0.8 km and 4.6 km, respectively. The decrease in the fluid flux, depth of the hydrothermal source, and the pressurization increase in E2 are likely associated to a magma reservoir. The decrease of fluid discharge in hydrothermal fields may reflect pressurization at depth potentially preceding hydrothermal explosions. This has significant implications for the longterm monitoring strategy of volcanoes.

The use of modern broadband seismometers allows the observation of dynamic and static near-field effects. In the fortunate case of the great 1994 Bolivia earthquake a 6 mm coseismic permanent offset was observed at distances of about 600 km. On the other hand no surface static displacement from moderate events has been observed yet. This is mainly due to the intrinsic difficulties in the instrument removal. In the present paper we analyze broadband waveforms from a couple of events in southern Italy, recorded at distance of 50 km, by applying the technique for instrument removal recently introduced by Zhu [2003]. We derive stable and reliable measures of very small coseismic static offset produced by moderate magnitude earthquakes. Our results, successfully tested against synthetic prediction, give permanent displacement of a few tenths of millimeters, one order of magnitude smaller than usual geodetic resolution.

Scattered waves observed at the seismographs of the National Italy’s seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the Southern Apennines, Italy. First, we investigate the coda-Q properties, then we apply theMLTWanalysis in the hypothesis of velocity and scattering coefficient constant with depth, and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient. Results obtained in the hypothesis of a uniform model show that a low scattering-Q−1 and a relatively higher intrinsic-Q−1 characterize the lithosphere of the Southern Apennines. Numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle, both with reasonable intrinsic dissipation coefficients. In these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values. This results lead to the consideration that scattering-Q−1 obtained using MLTW analysis under the assumption of uniform medium are overestimated. The values of the scattering-Q−1 estimated for Apennines at low frequency (1–2 Hz) in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world. The estimates obtained for frequencies ranging from 2 to 12 Hz are very low if compared with those obtained in the same hypothesis for other areas around the world. Coda Q−1 closely resembles intrinsic Q−1.

Just north of the island of Sicily, near the toe of Italy’s “boot,” a chain of volcanic islands traces a delicate arc in the Mediterranean Sea. This chain, the Aeolian Islands, popular tourist resorts in proximity to some of Earth’s most active and well-known volcanoes, including Etna and Stromboli. Lipari, the largest of these islands, lies of the island of Vulcano, for which these eruptive features are named. Lipari is less well characterized than some of the other nearby volcanoes, but one research group setting out to change this. This is the first time that a dense seismic array has been deployed to investigate a hydrothermal system in the volcanically active Aeolian Islands. Lipari is located ~80 kilometers north of the well-monitored Etna volcano. The island’s hydrothermal system, in which magma heats the water underground, is not to eruptive centers, but, rather, is connected to the regional fault system that delimits the western boundary of the active Ionian subduction zone. Lipari holds a unique place in our understanding of the tectonic evolution and hydrothermal activity of volcanoes emplaced in subduction zones (https://eos.org/projectupdates/ understanding-volcanic-eruptions-where-plates-meet). Within the framework of the ring-shaped Aeolian arc, the unexpected NNW–SSE alignment of Lipari andbeen related to a major regional discontinuity, the Tindari-Letojanni (https://www.researchgate.net/publication/311738886_Structural_architecture_and_active_deformation_pattern_in_the_northern_sector_of_the_Aeolian-Tindari- Letojanni_fault_system_SE_Tyrrhenian_Sea-NE_Sicily_from_integrated_analysis_of_field_marine_geophys) subduction transform edge propagator (STEP (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JB012202)) fault, a tear in a tectonic plate that allows one part of the plate to plunge downward while an adjacent remains on the surface.

On October 31, 2002 a ML=5.4 earthquake occurred in southern Italy, at the margin between the Apenninic thrust belt (to the west) and the Adriatic plate (to the east). In this area, neither historical event nor seismogenic fault is reported in the literature. In spite of its moderate magnitude, the earthquake caused severe damage in cities close to the epicenter and 27 people, out of a total of 29 casualties, were killed by the collapse of a primary school in S. Giuliano di Puglia. By inverting broadband regional waveforms, we computed moment tensor solutions for 15 events, as small as ML=3.5 (Mw=3.7). The obtained focal mechanisms show pure strike-slip geometry, mainly with focal planes oriented to NS (sinistral) and EW (dextral). In several solutions focal planes are rotated counterclockwise, in particular for later events, occurring west of the mainshock. From the relocated aftershock distribution, we found that the mainshock ruptured along an EW plane, and the fault mechanisms of some aftershocks were not consistent with the mainshock fault plane. The observed stress field, resulting from the stress tensor inversion, shows a maximum principal stress axis with an east–west trend (N83°W), whereas the minimum stress direction is almost N–S. Considering both the aftershock distribution and moment tensor solutions, it appears that several pre-existing faults were activated rather than a single planar fault associated with the mainshock. The finite fault analysis shows a very simple slip distribution with a slow rupture velocity of 1.1 km/s, that could explain the occurrence of a second mainshock about 30 h after. Finally, we attempt to interpret how the Molise sequence is related to the normal faulting system to the west (along the Apennines) and the dextral strike-slip Mattinata fault to the east.

We investigate an anomalous deep seismic sequence characterized by low-frequency bursts of earthquakes (maximum magnitude 5) that occurred between December 2013 and January 2014 in the southern Apenninic chain, Italy. Previous studies (Di Luccio et al., 2018) have shown evidences of fluid involvement in the earthquake nucleation process and identified thermal anomaly in nearby aquifers where CO2 of magmatic origin dissolves. Seismic source parameters reveal important information about the rupture mechanisms and stress field and their relation with the geological-tectonics processes. It is commonly assumed seismic source as pure shear dislocation described by a double-couple model. When volumetric changes occur, we need to consider the non-double couple source component in the description of the rupture process, as in geothermal and volcanic systems where fluids play an important role. In this study we analyze the 2013-2014 seismic sequence (earthquakes larger than 3) through a full moment tensor (FMT) inversion by using the HybridMT code (Kwiateck et al., 2016). The FMT is based on computing the integral of the first P-wave ground displacement pulse that is proportional to the seismic moment. Uncertainties of estimated FMTs are expressed by the normalized root-mean-squares between theoretical and observed amplitudes. The FMT technique is done on the vertical components of the seismograms, using a detailed 1D velocity model and accurate locations of the events. After a visual inspection of the waveforms based on the signal-to-noise ratio, we compute the displacement to estimate P-wave pulse polarities and the area beneath the P-pulse for each event and each station within epicentral distance comparable to the focal depth. The inversion procedure provides Mw, seismic moment and P, T and B axis orientation. Our results show high percentages of non-double couple components that vary over time and do not depend on earthquake magnitude. The stress axis orientations are in agreement with the regional crustal stress regime. The comparison of the obtained source parameters with petrological and geological data will allow us to better understand the emplacement mechanisms of intrusive bodies and the seismicity in mountain chains.

Seismic recordings are immediately available when an earthquake occurs. Their analysis allows the reconstruction of the rupture dynamics by means of sophisticated techniques, which usually need some tests to provide robust results. However, immediate information on the source kinematics is required in order to imagine the fault location and extent and quickly reconstruct the areas of stress release and subsequent accumulation. Very simple analysis may provide useful information, giving insight in source complexity. Right after the 6 April 2009 L'Aquila earthquake (MW = 6.3), we analyzed the seismograms recorded at broadband and strong motion stations and provided firm constraints on rupture kinematics, slip distribution, and static surface deformation, also discriminating the actual fault plane. The fracture occurred in two stages, with initial updip propagation, successively proceeding toward SE, possibly on a different plane. We also analyzed the strongest aftershock (MW = 5.6), showing that useful indications could be retrieved for lower magnitude events.

We introduce a new detection algorithm with improved local and regional seismic signal recognition. The method is based on the difference between seismic signals and background random noise in terms of fractal dimension D. We compare the new method extensively with standard methods currently in use at the Seismic Network of the lstituto Nazionale di Geofisica. Results from the comparisons show that the new method recognizes seismic phases detected by existing procedures, and in addition, it features a greater sensitivity to smaller signals, without an increase in the number of false alarms. The new method was tested on real continuous data and artificially simulated high-noise conditions and demonstrated a capability to recognize seismic signals in the presence of high noise. The efficiency of the method is due to a radically different approach to the topic, in that the assertion that a signal is fractal implies a relationship between the spectral amplitude of different frequencies. This relationship allows, for the fractal detector, a complete analysis of the entire frequency range under consideration.

To understand the source complexity of the April 6, 2009 L’Aquila earthquake (MW = 6.3), a quick seismological analysis is done on the waveforms of the mainshock and the larger aftershock that occurred on April 7, 2009. We prove that a simple waveform analysis gives useful insights into the source complexity, as soon as the seismograms are available after the earthquake occurrence, whereas the reconstruction of the rupture dynamics through the application of sophisticated techniques requires a definitely longer time. We analyzed the seismograms recorded at broadband and strong motion stations and provided firm constraints on rupture kinematics, slip distribution, and static surface deformation, also discriminating the actual fault plane. We found that two distinct rupture patches associated with different fracture propagation directions and possibly occurring on distinct rupture planes, characterized the source kinematics of the April 6 events. An initial updip propagation successively proceeds toward SE, possibly on a different plane. We also show that the same processing, applied to the April 7, 2009 aftershock (MW = 5.6), allows us to obtain useful information also in the case of lower magnitude events. Smaller events with similar location and source mechanism as the mainshock, to be used as Green’s empirical function, occur in the days before or within tens of minutes to a few hours after the mainshock. These quick, preliminary analyses can provide useful constraints for more refined studies, such as inversion of data for imaging the rupture evolution and the slip distribution on the fault plane. We suggest implementing these analyses for real, automatic or semi-automatic, investigations.

We applied ambient noise tomography to continuous data recorded by a dense seismic array deployed on the volcanic island of Lipari in the southern Tyrrhenian Sea. Since most of Lipari's seismicity occurs offshore and is not evenly distributed, this technique allowed us to obtain the first high-resolution images beneath the island down to ∼2.5 km depth. Results show a complex seismic structure related to the various ages and compositions of the volcanic products characteristic of the different regions of the island. High shear wave velocities are found in western Lipari, where active hydrothermal vents and N-S faults are mapped. Low wave speeds are revealed beneath southern and northeastern Lipari, where more recent volcanic activity developed along N-S dike-like structures that are aligned with rhyolitic vents. We suggest these dikes likely represent the probable pathways of future volcanic eruptions.