ALBERT

Description: Thermobarometry provides a critical means of assessing locations of magma storage and dynamics in the lead-up to volcanic eruptions and crustal growth. A common approach is to utilise minerals that have compositions sensitive to changes in pressure and/or temperature, such as clinopyroxene, which is ubiquitous in mafic to intermediate magmas. However, clinopyroxene thermobarometry may carry significant uncertainty and require an appropriate equilibrium melt composition. In addition, the degree of magma undercooling (ΔT) affects clinopyroxene composition and zoning, with common sector zoning potentially obfuscating thermobarometry results. Here, we use a set of crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy) at ΔT = 25–233 °C, P = 400–800 MPa, H2O = 0–4 wt % and fO2 = NNO + 2, with clinopyroxene crystals defined by Al-rich zones (prisms and skeletons) and Al-poor zones (hourglass and overgrowths) to assess common equilibrium models and thermobarometric approaches. Under the studied conditions, our data suggest that the commonly applied Fe–Mg exchange (cpx-meltKdFe–Mg) is insensitive to increasing ΔT and may not be a reliable indicator of equilibrium. The combined use of DiHd (CaMgSi2O6 + CaFeSi2O6) and EnFs (Mg2Si2O6 + Fe2Si2O6) models indicate the attainment of equilibrium in both Al-rich and Al-poor zones for almost all investigated ΔT. In contrast, CaTs (CaAl2SiO6) and CaTi (CaTiAl2O6) models reveal substantial deviations from equilibrium with increasing ΔT, particularly in Al-rich zones. We postulate that this reflects slower diffusion of Al and Ti in the melt compared with Ca and Mg and recommend the concurrent application of these four models to evaluate equilibrium between clinopyroxene and melt, particularly for sector-zoned crystals. Thermobarometers calibrated with only isothermal–isobaric experiments closely reproduce experimental P–T at low ΔT, equivalent to natural phenocrysts cores and sector-zoned mantles. Models that also consider decompression experiments are most accurate at high ΔT and are therefore suitable for outermost phenocryst rims and groundmass microlites. Recent machine learning approaches reproduce P–T conditions across all ΔT conditions. Applying our experimental constraints to sector-zoned microphenocrysts and groundmass microlites erupted during the 1974 eccentric eruption at Mt. Etna, we highlight that both hourglass and prism sectors are suitable for thermobarometry, given that equilibrium is sufficiently tested for. The combination of DiHd, EnFs, CaTs and CaTi models identifies compositions closest to equilibrium with the bulk melt composition, and results in smaller differences in P–T calculated for hourglass and prism sectors compared with applying only DiHd and EnFs equilibrium models. This provides a framework to assess crystallisation conditions recorded by sector-zoned clinopyroxene crystals in mafic alkaline settings.

Description: Published

Description: egad074

Description: OSV2: Complessità dei processi vulcanici: approcci multidisciplinari e multiparametrici

Description: JCR Journal

Description: We aim to compute macroseismic parameters (location and magnitude) using the BOXER code for the first time on the citizen testimonies, that is, individual intensity data points (IDPs) at the global scale collected and made available by the LastQuake system of the European–Mediterranean Seismological Centre (EMSC). IDPs available for different earthquakes are selected to eliminate those that are geographically inconsistent with most data; then they are clustered spatially based on various methods. For each cluster with at least three IDPs, a macroseismic data point (MDP), corresponding to an intensity value assessed for given localities as in classical macroseismic studies, is computed by various central tendency estimators (average, median, and trimmed averages). Finally, macroseismic parameters are obtained by MDP distribution using two location methods of BOXER code. For each earthquake, we used raw and corrected intensities and 132 different combinations of grouping methods, estimators, and BOXER methods. We assigned a ranking to the combinations that best reproduce instrumental parameters and used such a ranking to select preferred combinations for each earthquake. We analyzed retrospectively the reliability of the parameters as a function of time and space. The results are essentially identical using original and corrected intensities and show higher reliability for BOXER’s method 1 than for method 0; they are dependent on the geographical area, and generally improve over time and with the number of IDPs collected. These findings are useful for the future real-time analyses, and for evaluating the location and magnitude of earthquakes whenever a sufficient number of IDPs are available and with a distribution such that MDPs can be derived and the BOXER method applied.

Description: Published

Description: 969–996

Description: OST4 Descrizione in tempo reale del terremoto, del maremoto, loro predicibilità e impatto

Description: JCR Journal

Description: Underdetermination is a condition affecting all problems in seismic imaging. It manifests mainly in the nonuniqueness of the models inferred from the data. This condition is exacerbated if simplifying hypotheses like isotropy are discarded in favor of more realistic anisotropic models that, although supported by seismological evidence, require more free parameters. Investigating the connections between underdetermination and anisotropy requires the implementation of solvers which explore the whole family of possibilities behind nonuniqueness and allow for more informed conclusions about the interpretation of the seismic models. Because these aspects cannot be investigated using traditional iterative linearized inversion schemes with regularization constraints that collapse the infinite possible models into a unique solution, we explore the application of transdimensional Bayesian Monte Carlo sampling to address the consequences of underdetermination in anisotropic seismic imaging. We show how teleseismic waves of P and S phases can constrain upper‐mantle anisotropy and the amount of additional information these data provide in terms of uncertainty and trade‐offs among multiple fields.

Description: Published

Description: 1214–1226

Description: OST1 Alla ricerca dei Motori Geodinamici

Description: JCR Journal

Description: The Algerian offshore earthquake of 18 March 2021, Mw 6.0, was felt by people in various Italian regions, also at large epicentral distance. This unusual human perception far from the source prompted us to analyze the waveforms recorded by land seismic stations installed along the Iberian, French, and Italian coasts. On some seismograms of the selected network, prominent T phases are detected. T waves can travel in the SOund Fixing And Ranging (SOFAR) channel over great distances (thousands of kilometers) with little loss in signal strength and be recorded by near‐coastal seismometers after the P (primary) and S (secondary) phases (hence T or tertiary phases). To explain the subjective perception of ground shaking with quantities that are measured on the seismogram, we estimated the empirical macroseismic intensities for both body and T phases and we calculated the body‐wave seismic attenuation. The P‐wave anelastic attenuation analysis shows two main wave propagation patterns that reflect lithosphere heterogeneity of the Algerian, Liguro‐Provençal, and Tyrrhenian basins. We find that in some cases, in particular along the Italian and French coasts, the largest ground shaking is caused by the T phase. Our observations confirm that the central‐western Mediterranean Sea is a favorable site for T‐wave propagation and suggest that the T phases should be taken into account in ground‐shaking hazard assessment for the central‐western Mediterranean.

Description: Published

Description: 859–869

Description: OST2 Deformazione e Hazard sismico e da maremoto

Description: JCR Journal

Description: Werecomputethecoefficients of the intensity prediction equation (IPE) in Italy using the data of the DBMI15 version 2.0 (v.2.0) intensity database and the instrumental and combined (instrumental plus macroseismic) magnitudes reported by the CPTI15 v.2.0 catalog. Wefollow the same procedure described in the previous article, consisting of a first step in which the attenuation of intensity I with respect to the distance D from macroseismic hypocenter is referred to the expected intensity at the epicenter IE and a second step in which IE is related to the instrumental magnitude Mi, the combined magnitude Mc,the epicentral intensity I0, and the maximum intensity Imax using error-in-variable (EIV) regression methods. The main methodological difference with respect to the original article concerns the estimation of the uncertainty of IE to be used for EIV regressions, which is empirically derived from the standard deviation of regression between IE and Mi and also used for the regressions of IE with Mc, I0,andImax. In summary, the new IPE determined from DBMI15 v.2.0 is I IE−0:0081D−h−1:072 lnD−lnh , in which D p R2 h2 , h = 4.49 km, and IE can be calculated from the intensity data distribution of the earthquake. If the intensity data distribution is not available, IE can be calculated from the following relationships IE −2:578 1:867Mw,IE I0.

Description: In press

Description: OST2 Deformazione e Hazard sismico e da maremoto

Description: JCR Journal

Description: We analyze the interplay between hydrology, deformation and seismicity in the Matese massif, located in the Italian Southern Apennines. We find that this area is characterized by the concurrent action of two hydrologically-driven processes: the first is the deformation detected by GNSS data in the shallowest part (above the elevation of the major springs) of the Earth crust, in phase with the hydrological forcing; the second is the triggering of seismicity at depth with a delay suggesting a downward diffusive process. We study the first process by applying a Principal Component Analysis to the GNSS displacements time series, aiming to identify a common signal describing the largest data variance. We find that the maximum horizontal displacements associated with the first principal component (PC1) are larger than 1 cm in two GNSS sites and the PC1 temporal evolution is well correlated and in phase with the flow of the largest spring of the region, which we consider as proxy of the water content of the massif. This suggests that the main source of horizontal deformation is the water content fluctuations in the shallow portion of the Matese aquifer, in particular within fractures located in correspondence of the main mapped faults. The deformation rates caused by this process are one order of magnitude larger than the tectonic ones. Finally, we infer the second process by observing the correlation between the background seismicity and the spring discharge with a time lag of 121 days. In our interpretation, downward diffusive processes, driven by aquifer water content variations, propagate pore pressure waves that affect the faults strength favoring the occurrence of micro-earthquakes. This is supported by the values of hydraulic diffusivity (1.5 m^2/s) and rock permeability (3.2-3.8⋅10^−13 m^2), which are compatible with what is observed in karstified limestones.

Description: Published

Description: 1899–1912

Description: OST2 Deformazione e Hazard sismico e da maremoto

Description: JCR Journal

Description: The Turkey heat flow database includes several research articles obtained from the catalogue of The Global Heat Flow Data Assessment Project conducted by the International Heat Flow Commission (IHFC; www.ihfc-iugg.org). The presented database contains 725 heat-flow determinations compiled from 9 different publications generated between 1991-2023 reported within Turkey. For the reporting and sorting of the database, the structure documented by Fuchs et al. (2023) is followed. Within this dataset, 98% of the entries represent continental heat-flow data (onshore), while the remaining 2% correspond to marine data (offshore). 88% of the reported heat flow values were obtained via direct temperature measurements, while the remaining data (12%) were estimated from indirect Curie depth temperature calculations.

Description: In diesem Bericht werden die durch das GFZ Potsdam am 29. und 30. November 2023 durchgeführte bohrlochgeophysikalische Messungen in den Bohrungen Gt Khn 1/88 und Gt Khn 2/87 in Karlshagen (Mecklenburg-Vorpommern) dokumen-tiert. Die Messungen wurden mit dem Ziel der Gewinnung hochaufgelöster und un-gestörter Temperatur-Tiefen-Profile durchgeführt. Die Stillstandszeiten seit Erstel-lung liegen bei mehreren Jahrzehnten; jene seit letzter Befahrung bei fünfzehn Jahren, weshalb von ungestörten Gebirgstemperaturen ausgegangen werden kann. In der Bohrung Gt Khn 2/87 wurde bei 1786,5 m Teufe eine Temperatur von 57,8 °C, welches einem mittleren Temperaturgradienten von 27,8 °C/km entspricht, ge-messen. Die Bohrung Gt Khn 1/88 konnte bis zu einer Teufe von 325,1 m befahren werden, die gemessene Temperatur betrug 16,2 °C, der entsprechende mittlere ge-othermische Gradient beträgt ca. 23,6 °C/km. This report documents the borehole geophysical logging performed by GFZ Potsdam in the Gt Khn 1/88 and Gt Khn 2/87 boreholes in Karlshagen (Mecklenburg-Western Pomerania) on the 29th and 30th of November 2023. The measurements were conducted to achieve high-resolution and undisturbed temperature-depth pro-files. The shut-in times since the boreholes were drilled are several decades; the shut-in time since last activities in the boreholes are in the order of 15 years. There-fore, undisturbed formation temperatures can be expected in the boreholes. In the Gt Khn 2/87 borehole, a temperature of 57.8 °C was measured at a depth of 1786.5 m, which corresponds to an average temperature gradient of 27.8 °C/km. The Gt Khn 1/88 borehole could be logged to a depth of 325.1 m and the measured temperature at this depth was 16.2 °C, corresponding to an average geothermal gradient of approx. 23.6 °C/km.

Description: The data publication contains the compilation of global heat-flow data by the International Heat Flow Commission (IHFC; www.ihfc-iugg.org) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI). The presented data update release 2024 contains data generated between 1939 and 2024 and constitutes the second intermediate update benefiting from the global collaborative assessment and quality control of the Global Heat Flow Database running since May 2021 (http://assessment.ihfc-iugg.org). The data release comprises new original heat-flow data published since April 2023 (the update 2023). It contains 91,182 heat-flow data from 1,586 publications. 57% of the reported heat-flow values are from the continental domain (n ~ 54,553), while the remaining 43% are located in the oceanic domain (n ~ 36,692).

Description: The dataset contains source parameters of acoustic emission (AE) events recorded during triaxial friction (stick-slip) experiments performed on the Westerly Granite sample WgN05. In addition we provide raw waveform data of AE events recorded in triggered mode with a network of 16 AE sensors. Basic seismic catalog associated with the stick-slip experiment contains origin time, hypocentral location in local Cartesian coordinate system of the sample (with associated uncertainties), and AE-derived magnitude. In addition, for a subset of AEs we provide full moment tensors. This catalog include information on fault parameters (strike, dip and rake of the two nodal planes), percentage of isotropic, compensated linear vector dipole and double-couple components of the full moment tensor, P, T, B axes orientations in the coordinate system of the sample, uncertainty assessment, as well as the six independent moment tensor components. Finally, we provide a time series of axial stress values as presented in the Kwiatek et al. (2023) as well as the coordinates of the AE sensors. The catalog and parametric data is supplemented with the raw waveform recordings stored in HDF5 format from 16 acoustic emission sensors placed on the surface of the sample.