Assessing the seismic coupling of shallow continental faults and its impact on seismic hazard estimates: a case-study from Italy

We propose an objective and reproducible algorithmic path to forecast seismicity in Italy from long-term deformation models. These models are appropriate for Italy and its neighbouring countries and seas thanks to the availability of rich, reliable and regularly updated historical earthquake and seismogenic fault databases, and to the density of permanent GPS stations. However, so far little has been done to assess the seismic coupling of Italian active faults, that is to quantify their ability to release earthquakes. This must be determined in order to use geodetic and active faulting observations in alternative seismicity models, to overcome possible limitations of the earthquake record for the assessment of seismic hazard. We use a probabilistic method to assign upper crustal earthquakes from the historical catalogue to their presumed causative faults, then collect all the events into three subcatalogues corresponding to the compressional, extensional and strike-slip faulting classes. We then determine the parameters of their Gutenberg–Richter frequency/magnitude relations using maximum-likelihood methods and integrate these distributions to estimate the long-term seismic moment rate for each class. Finally, we compare these seismicity rates to the long-term tectonic deformation based on GPS data, thus determining the coupled thickness (and estimating seismic coupling) for each fault class. We find that in our study region the seismic coupling and the related coupled thickness is on average two times larger for extensional than for compressional faults. As for the spatial distribution of earthquake rates, a larger number of events is predicted for the extensional settings of the Apennines chain, in agreement with the inferred seismic coupling but also with the long-term strain rates. We also find that the frequency/magnitude distributions indicate that the largest earthquakes occur in extensional settings, whereas compressional faults are expected to host comparatively smaller events.Published32-471T. Deformazione crostale attivaJCR Journa

Spectral elements numerical simulation of the 2009 L’Aquila earthquake on a detailed reconstructed domain

In this paper we simulate the earthquake that hit the city of L’Aquila on the 6th of April 2009 using SPEED (SPectral Elements in Elastodynamics with Discontinuous Galerkin), an open-source code able to simulate the propagation of seismic waves in complex three-dimensional (3D) domains. Our model includes an accurate 3D reconstruction of the Quaternary deposits, according to the most up-to-date data obtained from the Microzonation studies in Central Italy and a detailed model of the topography incorporated using a newly developed tool (May et al. 2021). The sensitivity of our results with respect to different kinematic seismic sources is investigated. The results obtained are in good agreement with the recordings at the available seismic stations at epicentral distances within a range of 20km. Finally, a blind source prediction scenario application shows a reasonably good agreement between simulations and recordings can be obtained by simulating stochastic rupture realizations with basic input data. These results, although limited to nine simulated scenarios, demonstrate that it is possible to obtain a satisfactory reconstruction of a ground shaking scenario employing a stochastic source constrained on a limited amount of ex-ante information. A similar approach can be used to model future and past earthquakes for which little or no information is typically available, with potential relevant implications for seismic risk assessment

Interseismic creep of carbonate-hosted seismogenic normal faults (central Italy)

It is crucial to comprehend the fault slip behavior in carbonate formations as they are potential sites of earthquake initiation. We studied three carbonate-hosted seismogenic normal faults in the northern Apennines by using (micro)structural and geochemical analyses of fault rocks combined with new seismic coupling estimates. The (upper bound) seismic coupling is 0.75, meaning that at least 25% of the study-area long-term deformation is released aseismically in the upper crust. Microscopy and electron-backscatter diffraction analysis reveal that whereas the localized principal slip zone records seismic slip (as ultracataclastic material, calcite crystallographic preferred orientation - CPO, truncated clasts, and possibly mirror-slip surfaces), the bulk fault rock below behaves differently. Cataclasites in massive limestones deform by cataclastic flow, intergranular pressure solution, and crystal plasticity, with CPO development. Foliated tectonites in micritic limestones deform by pressure solution and frictional sliding, with CPO development. We suggest these mechanisms accommodate on-fault interseismic creep. This is consistent with experimental results reporting velocity-strengthening behavior at low slip rates. Models of fault slip behavior usually assume that (i) seismic vs. aseismic slip take place in separate fault patches, (ii) creep is limited to lithology-controlled weak domains, and (iii) rate-weakening patches are interseismically locked. We herein bring multi-scale clues of co-existing seismic and aseismic sliding along the same fault in limestones at different times during the seismic cycle. Our results imply that on-fault aseismic motion must be added to seismic slip to pair the long-term deformation rates and that creep is not exclusive of phyllosilicate-bearing units. Our work provides new insights into the fault slip behavior in carbonate rocks and may profoundly impact the comprehension of the seismic cycle and fault seismogenic potential

No evidence of increased cerebrovascular involvement in adult neurologically-asymptomatic β-Thalassaemia. A multicentre multimodal magnetic resonance study

Multi-factorial causes jeopardize brain integrity in β-thalassaemia. Intracranial parenchymal and vascular changes have been reported among young β-thalassaemia patients but conventional magnetic resonance imaging (MRI) findings are contradictory making early MRI and magnetic resonance angiography (MRA)/venography monitoring a matter of debate. This study prospectively investigated 75 neurologically asymptomatic β-thalassaemia patients (mean-age 35·2 ± 10·7 years; 52/75 transfusion-dependent; 41/75 splenectomised) using a 3T magnetic resonance scanner; clinical, laboratory and treatment data were also collected. White matter ischaemic-like abnormalities, intracranial artery stenoses, aneurysms and sinus venous thrombosis were compared between patients and 56 healthy controls (mean-age 33·9 ± 10·8 years). No patient or control showed silent territorial or lacunar strokes, intracranial artery stenoses or signs of sinus thrombosis. White matter lesions were found both in patients (35/75, 46·7%) and controls (28/56, 50·0%), without differences in terms of number (4·0 ± 10·6 vs. 4·6 ± 9·1, P = 0·63), size and Fazekas' Score. Intracranial aneurysms did not differ between patients and controls for incidence rate (7/75, 9·3% vs. 5/56, 8·9%), size and site. Vascular and parenchymal abnormality rate did not differ according to treatments or clinical phenotype. According to this study, asymptomatic β-thalassaemia patients treated according to current guidelines do not seem to carry an increased risk of brain and intracranial vascular changes, thus weakening recommendations for regular brain MRI monitoring

Auditory cortex hypoperfusion: a metabolic hallmark in Beta Thalassemia

Background: Sensorineural hearing loss in beta-thalassemia is common and it is generally associated with iron chelation therapy. However, data are scarce, especially on adult populations, and a possible involvement of the central auditory areas has not been investigated yet. We performed a multicenter cross-sectional audiological and single-center 3Tesla brain perfusion MRI study enrolling 77 transfusion-dependent/non transfusion-dependent adult patients and 56 healthy controls. Pure tone audiometry, demographics, clinical/laboratory and cognitive functioning data were recorded. Results: Half of patients (52%) presented with high-frequency hearing deficit, with overt hypoacusia (Pure Tone Average (PTA) > 25\ua0dB) in 35%, irrespective of iron chelation or clinical phenotype. Bilateral voxel clusters of significant relative hypoperfusion were found in the auditory cortex of beta-thalassemia patients, regardless of clinical phenotype. In controls and transfusion-dependent (but not in non-transfusion-dependent) patients, the relative auditory cortex perfusion values increased linearly with age (p < 0.04). Relative auditory cortex perfusion values showed a significant U-shaped correlation with PTA values among hearing loss patients, and a linear correlation with the full scale intelligence quotient (right side p = 0.01, left side p = 0.02) with its domain related to communication skills (right side p = 0.04, left side p = 0.07) in controls but not in beta-thalassemia patients. Audiometric test results did not correlate to cognitive test scores in any subgroup. Conclusions: In conclusion, primary auditory cortex perfusion changes are a metabolic hallmark of adult beta-thalassemia, thus suggesting complex remodeling of the hearing function, that occurs regardless of chelation therapy and before clinically manifest hearing loss. The cognitive impact of perfusion changes is intriguing but requires further investigations