Variable plate kinematics promotes changes in back-arc deformation regime along the north-eastern Eurasia plate boundary.

The stretching of the lithosphere leading to back-arc basins formation generally develops behind arc-trench systems and is considered the consequence of slab retreat relative to the upper plate. Here, we examine the deformation regime evolution within the overriding plate due to subduction processes, using thermo-mechanical numerical simulations. We explore the north-eastern Eurasia plate boundary and the mechanisms of subducting Pacific plate since 57 Ma. During this time interval, several extensional basins formed along the Eurasia margin, such as the East China Sea, the Japan Sea, and the Kuril basin. Here, we increased the simulation complexity, with the inclusion of (i) the kinematic variability of the Pacific plate over the geological past with respect to a fixed Eurasia, incorporating time-dependent (i.e., temporally evolving) velocities computed from plate motion reconstructions; (ii) a Low-Velocity Zone within the asthenosphere, and (iii) a horizontal eastward mantle flow. Our results show a crucial role of the mantle flow for the development of lithospheric extension and back-arc basin opening, and a main kinematic control of the subduction trench position, which advances and retreats, into distance intervals in the order of ∼  100 km, and providing stages of compression and extension in a back-arc basin.

Clustering Analysis of Seismicity in the Anatolian Region with Implications for Seismic Hazard.

The Anatolian region is one of the most seismically active tectonic settings in the world. Here, we perform a clustering analysis of Turkish seismicity using an updated version of the Turkish Homogenized Earthquake Catalogue (TURHEC), which contains the recent developments of the still ongoing Kahramanmaras seismic sequence. We show that some statistical properties of seismic activity are related to the regional seismogenic potential. Mapping the local and global coefficients of variation of inter-event times of crustal seismicity which occurred during the last three decades, we find that territories prone to major seismic events during the last century usually host globally clustered and locally Poissonian seismic activity. We suggest that regions with seismicity associated with higher values of the global coefficient of variation of inter-event times, CV, are likely to be more prone to hosting large earthquakes in the near future than other regions characterized by lower values, if their largest seismic events have the same magnitude. If our hypothesis is confirmed, clustering properties should be considered as a possible additional information source for the assessment of seismic hazard. We also find positive correlations between global clustering properties, the maximum magnitude and the seismic rate, while the b-value of the Gutenberg-Richter law is weakly correlated with them. Finally, we identify possible changes in such parameters before and during the 2023 Kahramanmaras seismic sequence.

Correlation between seismic activity and tidal stress perturbations highlights growing instability within the brittle crust.

Faults become more and more responsive to stress perturbations as instability mounts. We utilize this property in order to identify the different phases of the seismic cycle. Our analysis provides new insights about the features of impending mainshocks, which are proposed to emerge from a large-scale crustal-weakening preparation process whose duration depends on their seismic moments, according to the power-law T [Formula: see text] M[Formula: see text] for M[Formula: see text] [Formula: see text] 10[Formula: see text] N m. Moreover, further studies are performed about the impact of tidal stress perturbation on seismicity; in particular, the relationship between frequency-magnitude scaling and perturbations is discussed, showing that the sensitivity of earthquakes to solid Earth tides decreases as their magnitudes increase.

A heterogeneous subcontinental mantle under the African-Arabian Plate boundary revealed by boron and radiogenic isotopes.

The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-lasting (early Miocene to Pleistocene) Na-alkali basaltic volcanism, sourced in the asthenosphere mantle. The upwelling asthenosphere at the Africa-Arabia margin produces very limited magma volumes in the axial zone. Therefore, portions of hot, fertile mantle continue their eastward migration and are stored at shallower depths under the 100-km thick Arabian lithosphere, which is much thinner than the African one (≈175 km): this causes the occurrence and 20-Ma persistence of magma supply under the study area. Erupted basalts sampled a continuous variation of the mantle source, with a striking correlation among temperature, pressure and isotopic composition shifting between two end members: a 100 km-deep, more depleted source, and a 60 km-deep, more enriched one. In particular, we observed an unusual variation in boron isotopes, which in the oceanic domain does not vary between more depleted and more enriched mantle sources. This study shows that, at least in the considered region, subcontinental mantle is more heterogeneous than the suboceanic one, and able to record for very long times recycling of shallow material.

New observations in Central Italy of groundwater responses to the worldwide seismicity.

Chemical and physical responses of groundwater to seismicity have been documented for thousands of years. Among the waves produced by earthquakes, Rayleigh waves can spread to great distances and produce hydrogeological perturbations in response to their passage. In this work, the groundwater level, which was continuously recorded in a monitoring well in Central Italy between July 2014 and December 2019, exhibited evident responses to dynamic crustal stress. In detail, 18 sharp variations of the groundwater level due to worldwide Mw ≥ 6.5 earthquakes were observed. Apart from earthquakes that occurred in Papua New Guinea and those with a hypocentral depth > 150 km, all far away Mw ≥ 7.6 earthquakes produced impulsive oscillations of groundwater. As the earthquake magnitude decreased, only some earthquakes with 6.5 ≤ Mw < 7.6 caused groundwater level perturbations, depending on the data acquisition frequency and epicentral distance from the monitoring well. A clear correlation between earthquake distance and magnitude in hydrogeological responses was found. Our results shed light on the hydrosensitivity of the study site and on the characteristics of fractured aquifer systems. Detecting the water table variations induced by distant earthquakes is another step towards a correct identification of (preseismic) hydrogeological changes due to near-field seismicity.

Volume unbalance on the 2016 Amatrice - Norcia (Central Italy) seismic sequence and insights on normal fault earthquake mechanism.

We analyse the Mw 6.5, 2016 Amatrice-Norcia (Central Italy) seismic sequence by means of InSAR, GPS, seismological and geologic data. The >1000 km2 area affected by deformation is involving a volume of about 6000 km3 and the relocated seismicity is widely distributed in the hangingwall of the master fault system and the conjugate antithetic faults. Noteworthy, the coseismically subsided hangingwall volume is about 0.12 km3, whereas the uplifted adjacent volumes uplifted only 0.016 km3. Therefore, the subsided volume was about 7.5 times larger than the uplifted one. The coseismic motion requires equivalent volume at depth absorbing the hangingwall downward movement. This unbalance regularly occurs in normal fault-related earthquakes and can be inferred as a significant contribution to coseismic strain accomodated by a stress-drop driven collapse of precursory dilatancy. The vertical coseismic displacement is in fact larger than the horizontal component, consistent with the vertical orientation of the maximum lithostatic stress tensor.

New insights into earthquake precursors from InSAR.

We measured ground displacements before and after the 2009 L'Aquila earthquake using multi-temporal InSAR techniques to identify seismic precursor signals. We estimated the ground deformation and its temporal evolution by exploiting a large dataset of SAR imagery that spans seventy-two months before and sixteen months after the mainshock. These satellite data show that up to 15 mm of subsidence occurred beginning three years before the mainshock. This deformation occurred within two Quaternary basins that are located close to the epicentral area and are filled with sediments hosting multi-layer aquifers. After the earthquake, the same basins experienced up to 12 mm of uplift over approximately nine months. Before the earthquake, the rocks at depth dilated, and fractures opened. Consequently, fluids migrated into the dilated volume, thereby lowering the groundwater table in the carbonate hydrostructures and in the hydrologically connected multi-layer aquifers within the basins. This process caused the elastic consolidation of the fine-grained sediments within the basins, resulting in the detected subsidence. After the earthquake, the fractures closed, and the deep fluids were squeezed out. The pre-seismic ground displacements were then recovered because the groundwater table rose and natural recharge of the shallow multi-layer aquifers occurred, which caused the observed uplift.

Hydrogeochemical changes before and during the 2016 Amatrice-Norcia seismic sequence (central Italy).

Seismic precursors are an as yet unattained frontier in earthquake studies. With the aim of making a step towards this frontier, we present a hydrogeochemical dataset associated with the 2016 Amatrice-Norcia seismic sequence (central Apennines, Italy), developed from August 24th, with an Mw 6.0 event, and culminating on October 30th, with an Mw 6.5 mainshock. The seismic sequence occurred during a seasonal depletion of hydrostructures, and the four strongest earthquakes (Mw ≥ 5.5) generated an abrupt uplift of the water level, recorded up to 100 km away from the mainshock area. Monitoring a set of selected springs in the central Apennines, a few hydrogeochemical anomalies were observed months before the onset of the seismic swarm, including a variation of pH values and an increase of As, V, and Fe concentrations. Cr concentrations increased immediately after the onset of the seismic sequence. On November 2016, these elements recovered to their usual low concentrations. We interpret these geochemical anomalies as reliable seismic precursors for a dilational tectonic setting.

Anti-hepatitis C virus treatment may prevent the progression of liver fibrosis in non-responder human immunodeficiency virus/hepatitis C virus coinfected patients

AIM: To evaluate changes in liver histology in patients with human immunodeficiency virus/hepatitis C virus coinfection non-responders to a suboptimal Interferon+Ribavirine regimen. MATERIALS AND METHODS: We investigated 49 patients with two sequential liver biopsies: 18 were non-responders to Interferon+Ribavirine treatment (Group hepatitis C virus Rx) administered after the 1st liver biopsy who underwent a 2nd liver biopsy after a median period of 3.92 year and 31 were patients who remained untreated for hepatitis C virus disease (Group hepatitis C virus untreated) after the 1st liver biopsy because of refusal and underwent a 2nd liver biopsy after a median period of 5.05-years. Most patients in both groups were under highly active antiretroviral therapy. At the time of 1st liver biopsy similar degrees of necro-inflammation, fibrosis and steatosis were observed in both groups. Changes in liver lesions between 1st and 2nd liver biopsys were adjusted for different intervals between liver biopsys by a mathematic formula. RESULTS: Liver fibrosis did not change in 88.9% of patients in Group hepatitis C virus Rx and in 77.4% in Group hepatitis C virus untreated. A marked deterioration in liver fibrosis was observed in 5 (16%) patients in Group hepatitis C virus untreated and in none in Group hepatitis C virus treated. Necro-inflammation and steatosis remained substantially unchanged in both groups. CONCLUSION: Liver histology remained substantially unchanged in human immunodeficiency virus/hepatitis C virus patients non-responder to anti-hepatitis C virus therapy over 4 years observation, suggesting an effective anti-hepatitis C virus early treatment for all hepatitis C virus/human immunodeficiency virus coinfected patients who can reasonably tolerate therapy. .

Anti-hepatitis C virus treatment may prevent the progression of liver fibrosis in non-responder human immunodeficiency virus/hepatitis C virus coinfected patients.

AIM: To evaluate changes in liver histology in patients with human immunodeficiency virus/hepatitis C virus coinfection non-responders to a suboptimal Interferon+Ribavirine regimen. MATERIALS AND METHODS: We investigated 49 patients with two sequential liver biopsies: 18 were non-responders to Interferon+Ribavirine treatment (Group hepatitis C virus Rx) administered after the 1st liver biopsy who underwent a 2nd liver biopsy after a median period of 3.92 year and 31 were patients who remained untreated for hepatitis C virus disease (Group hepatitis C virus untreated) after the 1st liver biopsy because of refusal and underwent a 2nd liver biopsy after a median period of 5.05-years. Most patients in both groups were under highly active antiretroviral therapy. At the time of 1st liver biopsy similar degrees of necro-inflammation, fibrosis and steatosis were observed in both groups. Changes in liver lesions between 1st and 2nd liver biopsys were adjusted for different intervals between liver biopsys by a mathematic formula. RESULTS: Liver fibrosis did not change in 88.9% of patients in Group hepatitis C virus Rx and in 77.4% in Group hepatitis C virus untreated. A marked deterioration in liver fibrosis was observed in 5 (16%) patients in Group hepatitis C virus untreated and in none in Group hepatitis C virus treated. Necro-inflammation and steatosis remained substantially unchanged in both groups. CONCLUSION: Liver histology remained substantially unchanged in human immunodeficiency virus/hepatitis C virus patients non-responder to anti-hepatitis C virus therapy over 4 years observation, suggesting an effective anti-hepatitis C virus early treatment for all hepatitis C virus/human immunodeficiency virus coinfected patients who can reasonably tolerate therapy.

The tectonic puzzle of the Messina area (Southern Italy): insights from new seismic reflection data.

The Messina Strait, that separates peninsular Italy from Sicily, is one of the most seismically active areas of the Mediterranean. The structure and seismotectonic setting of the region are poorly understood, although the area is highly populated and important infrastructures are planned there. New seismic reflection data have identified a number of faults, as well as a crustal scale NE-trending anticline few km north of the strait. These features are interpreted as due to active right-lateral transpression along the north-eastern Sicilian offshore, coexisting with extensional and right-lateral transtensional tectonics in the southern Messina Strait. This complex tectonic network appears to be controlled by independent and overlapping tectonic settings, due to the presence of a diffuse transfer zone between the SE-ward retreating Calabria subduction zone relative to slab advance in the western Sicilian side.

Uranium groundwater anomalies and L'Aquila earthquake, 6th April 2009 (Italy).

Monitoring of chemical and physical groundwater parameters has been carried out worldwide in seismogenic areas with the aim to test possible correlations between their spatial and temporal variations and strain processes. Uranium (U) groundwater anomalies were observed during the preparation phases of the recent L'Aquila earthquake of 6th April 2009 in the cataclastic rocks near the overthrust fault crossing the deep underground Gran Sasso National Laboratory. The results suggest that U may be used as a potential strain indicator of geodynamic processes occurring before the seismic swarm and the main earthquake shock. Moreover, this justifies the different radon patterns before and after the main shock: the radon releases during and after the earthquake are much than more during the preparatory period because the process does not include only the microfracturing induced by stress-strain activation, but also radon increases accompanying groundwater U anomalies.