Vannoli, Paola

We provide detailed sedimentological, paleontological, and tephrochronological data on a complex sedimentary succession cropping out in the Tyrrhenian coastal area of central Italy, which was deposited in response to sealevel rise during MIS 7, coeval with the Latera phase of activity in the Vulsini Volcanic District. Diffuse intercalations of primary volcanic layers erupted during this phase and their geochronologic and chemostratigraphical characterization based on 40Ar/39Ar dating and EMP analyses, allowed for the identification of three stacked aggradational successions separated by erosive phases and their correlation with the Oxygen isotope record and phases in the relative sea-level curve. The ages of the tephra layers strictly frame the sedimentation in the interval of 253–206 ka, providing independent dating to glacial Termination III and to the three sea-level oscillations during MIS 7e, 7c, and 7a. Moreover, micro- and macrofaunal-based analyses provide information on the paleoenvironments and bathymetry during the highstands, which complement the geomorphological analysis reconstructing the inner edges of the corresponding marine terraces, allowing us to assess precise maximum sea level reached during MIS 7e and MIS 7a. The results of this multidisciplinary study enable us to establish in great detail the chronology, dynamics, relative amplitude, and effects of the sea-level fluctuations in the Tyrrhenian Sea during the whole MIS 7, providing independent, precise geochronological constraints for this period.

In this study, we aimed to assess the capacity of a physics-based earthquake simulator to improve our understanding of the seismogenic process. In this respect, we applied a previously tested earthquake simulator to two well-known and completely different seismogenic fault systems, namely the Italian Apennines and the Nankai subduction in Japan, for which long historical records of strong earthquakes are available. They are characterized by different fault mechanisms, fault sizes, and slip rates. Because of the difference in slip rates, the time scale of the seismicity patterns is different for the two systems (several hundreds of years for the Apennines and a few tens of years for the Nankai Fault). The results of simulations that produced synthetic catalogues of 100,000 years show these significant long-term seismicity patterns characterizing the seismic cycles for both seismogenic areas as follows: The average stress and the occurrence rate of earthquakes increase in the long term as the next major earthquake approaches; while the average stress increases uniformly, the occurrence rate stops increasing well in advance of the mainshocks; the b-value exhibits a long-term increase before major earthquakes and a fast decrease shortly before the mainshocks. Even if no specific statistical tool was applied for the quantification of the similarities between the seismicity patterns of the two seismic areas, such similarities are clearly justified by the large number of seismic cycles included in the 100,000-year synthetic catalogues. The paper includes a discussion on the capability of the simulation algorithm to reliably represent the real long-term seismogenic process. This question is difficult to answer because the available historical observations are of too short a duration to provide significant statistical results. In spite of the limitations characterizing the use of earthquake simulators for time-dependent earthquake hazard assessment, and the lack of convincing mechanistic explanations of the specific seismic patterns reproduced by our simulator algorithm, our results encourage further investigations into the application of simulators for the development of seismogenic models, including short-term features.

We investigated the active tectonics and earthquake potential of the eastern Siena Basin, a slowly deforming portion of southern Tuscany in the inner Northern Apennines. This region hosts several historical settlements and valuable cultural heritage, but also frequent background seismicity and rare damaging earthquakes in the Mw range 5.0-6.2. We describe in detail an active, capable, and seismogenic fault system that we identified in the eastern Siena Basin, a few kilometres south-east of the city of Siena, thanks to the presence of an active quarry (Cava Capanni) that exploits travertines of Middle Pleistocene-Holocene age. Travertines are unique rock masses that may preserve living evidence of active and seismogenic faulting, thus providing remarkable seismotectonic insight. The active fault system consists of at least two segments rupturing travertines younger than 45 ka, with a cumulative vertical displacement of 111 cm, and an estimated minimum slip rate of 0.02-0.03 mm/y. We maintain that this displacement is the result of at least three coseismic movements accompanied by clastic dykes injected within the fault damage zone due to liquefaction phenomena. The fault system is seen to extend east of the quarry, affecting Pliocene and Mesozoic deposits. The Cava Capanni fault system is evidence of a poorly understood but potentially seismogenic tectonic mechanism of regional extent. Its orientation and kinematics are compatible with the activity of faults that are oriented obliquely or orthogonally to the main chain axis, in contrast with the setting of the axial and outer zone of the Northern Apennines, where extension and compression are accommodated by Apennines-parallel faults.

In this work, we present new biostratigraphic and paleoecological data from the Mignone River valley, located in the central sector of the Tyrrhenian Sea margin and part of the wider Tarquinia basin, and cores in the area of Rome. By combining the new paleontological information with a review of the extant literature, we re-examine the stratigraphic architecture of the Pliocene succession in the central sector of the northwestern Tyrrhenian Sea margin, spanning the Zanclean (MPl1; 5.33–5.08 Ma) through the early Piacenzian (MPl4b; 3.57–3.31 Ma), and of the following Pleistocene transgressive-regressive sequence, comprising the Gelasian (MPl6; 2.59–1.81 Ma) through the Santernian (MPl1; 1.81–1.5 Ma). We propose a revision of the paleogeographic evolution of the central Tyrrhenian Sea basins throughout the Pliocene-Lower Pleistocene interval, by coherently framing it within the chronology of the volcanic phases that occurred in this region. In particular, our reconstruction points toward the presence of a single Transgressive- Regressive (T-R) sequence starting with the Zanclean reflooding of the Mediterranean after the Messinian Salinity Crisis and ending in the Piacenzian, as opposed to the previously proposed occurrence of two depositional T-R sequences separated by an erosional phase affecting part of the Globorotalia puncticulata biozone.

Abstract Taking full advantage of good-quality historical earthquake and seismogenic source data available for Italy (Catalogo Parametrico dei Terremoti Italiani [CPTI15] and Database of Individual Seismogenic Sources [DISS] databases), we tested the regional variability of the b-value of the Gutenberg–Richter law, focusing on the dominantly extensional, nearly 1200-km-long seismogenic corridor straddling the Apennines chain; an 18,200  km2 area generating about 45% of the seismic moment released countrywide. We carefully chose and tested the most appropriate completeness interval and completeness magnitude (Mc), and used the Lilliefors method, the Utsu test, and a bootstrap technique to verify the quality of our results and inferences. The 0.65 b-value we obtained is substantially lower than b-values used in Italian seismic hazard models, often close to 1.0; yet it predicts more accurately the observed Apennines earthquake record, suggesting that most currently adopted magnitude-frequency distributions underpredict events in the Mw range 6.0–7.1 and overpredict those in the range 5.2–5.5. We also highlight that the time, space, and magnitude distribution of the largest Italian earthquakes hardly follows the Gutenberg–Richter law: it rather favors a characteristic behavior. We contend that the b-value is too critical of a parameter for being calculated using statistically weak data sets, such as those resulting from overly detailed area-source models: one may end up characterizing low-hazard areas more accurately than high-hazard areas. Conversely, we advocate the use of fewer, larger area sources that fully exploit the current understanding of regional seismotectonics, as a way of obtaining more realistic regional hazard models.

The prompt identification of faults responsible for moderate-to-large earthquakes is fundamental for understanding the likelihood of further, potentially damaging events. This is increasingly challenging when the activated fault is an offshore buried thrust, where neither coseismic surface ruptures nor GPS/InSAR deformation data are available after an earthquake. We show that on 9 November 2022, an Mw 5.5 earthquake offshore Pesaro ruptured a portion of the buried Northern Apennines thrust front (the Cornelia thrust system [CTS]). By post-processing and interpreting the seismic reflection profiles crossing this thrust system, we determined that the activated fault (CTS) is an arcuate 30-km-long, NW-SE striking, SW dipping thrust and that older structures at its footwall possibly influenced its position and geometry. The activation of adjacent segments of the thrust system is a plausible scenario that deserves to be further investigated to understand the full earthquake potential of this offshore seismogenic source.

We studied the long-term features of earthquakes caused by a fault system in the northern Adriatic sea that experienced a series of quakes beginning with two main shocks of magnitude 5.5 and 5.2 on 9 November 2022 at 06:07 and 06:08 UTC, respectively. This offshore fault system, identified through seismic reflection profiles, has a low slip rate of 0.2–0.5 mm/yr. As the historical record spanning a millennium does not extend beyond the inter-event time for the largest expected earthquakes (M ' 6.5), we used an earthquake simulator to generate a 100,000-year catalogue with 121 events of Mw 5.5. The simulation results showed a recurrence time (Tr) increasing from 800 yrs to 1700 yrs as the magnitude threshold increased from 5.5 to 6.5. However, the standard deviation s of inter-event times remained at a stable value of 700 yrs regardless of the magnitude threshold. This means that the coefficient of variation (Cv = s/Tr) decreased from 0.9 to 0.4 as the threshold magnitude increased from 5.5 to 6.5, making earthquakes more predictable over time for larger magnitudes. Our study supports the use of a renewal model for seismic hazard assessment in regions of moderate seismicity, especially when historical catalogues are not available.

In this paper we deal with statistical features of earthquakes, seeking possible correlations between the G-R magnitude distribution and the short-term clustering in an area of the Central Apennines, Italy, where significant seismicity with earthquakes exceeding magnitude 6.0 has been repeatedly observed from 1990 to the present. For this purpose, a recently developed version of the ETAS model, incorporating a threedimensional spatial triggering kernel, has been adopted. Our analysis has been carried out representing the b-value and the probability of independence of events on six vertical cross-sections suitably related to the seismic structures that are considered responsible of the seismicity observed in the study area. The results of the statistical analysis of the seismicity in the study area have shown a clear distinction between the western normal low-angle fault system, characterized by eastward dip, and the eastern normal fault systems, with westward dip. In the former (Etrurian Fault System; EFS) we found seismicity with a high b-value and high probability of independence, i.e., a scarce capacity of producing clusters and strong aftershock sequences. The eastern fault systems of our study area are distinguishable in two main distinct systems, which generated two strong seismic sequences in 1997 and 2016-2017. In the former (Colfiorito) sequence the seismicity showed a very low b-value and a modest probability of independence, while in the latter (Central Italy) sequence the bvalue was significantly higher and the probability of independence had extremely low values (manifesting a high level of clustering). The much higher b-value of the EFS than the other extensional sources could be caused by its peculiar seismotectonic role of discontinuity at the base of the normal active faulting, and its reduced capacity of accumulating stress. This circumstance may be interpreted by a difference in the rheological properties of these fault systems, possibly also in relation to their present status in the earthquake cycle and the presence of strong aftershock sequences.

This paper is intended as a short presentation of the main limitations affecting seismic hazard assessment, revisiting possible methods available in the literature to be applied for this purpose. The convergence of the African Plate with the Eurasian Plate is the cause of the high seismic activity characterizing the Mediterranean region, with particular intensity in its eastern part. It is clear that the associated seismic risk requires appropriate measures for its mitigation. Seismic risk, the amount of resources that the community is expected to pay to earthquakes in the long term, is the product of three factors, such as seismic hazard, vulnerability and value of the exposed goods. As earthquakes cannot be prevented, seismic risk can be mitigated by improving our knowledge of seismic hazard, which is largely based on statistical analysis of historical earthquake catalogs. Nevertheless, historical records are affected by problems of reliability, completeness and shortness, as they commonly span time lengths of the same order of magnitude or even shorter than the inter-event time of the strongest earthquakes produced by specific seismic sources. In this respect, alternative methods can be proposed for integrating and improving our knowledge of seismogenic processes, and estimating both time-independent and time-dependent occurrence rates of strong earthquakes. We propose the application of physics-based earthquake simulators, requiring the knowledge of a robust geological-geophysical seismogenic model.

The Italian historical earthquake record is among the richest worldwide; as such it allows for the development of advanced techniques for retrieving quantitative information by calibration with recent earthquakes. Building on a pilot elaboration of northern Italian earthquakes, we developed a procedure for determining the hypocentral depth of all Italian earthquakes from macroseismic intensity data alone. In a second step the procedure calculates their magnitude, taking into account the inferred depth. Hypocentral depth exhibits substantial variability countrywide but has so far received little attention: pre-instrumental earthquakes were routinely “flattened” at the upper-crustal level (∼10 km), on the grounds that the calculation of hypocentral depth is heavily dependent on the largely unknown local propagation properties. We gathered a learning set of 42 earthquakes documented by reliable instrumental data and by numerous macroseismic intensity observations. We observe (1) that within 50 km from the epicenter the ground motion attenuation rate is primarily controlled by hypocentral depth and largely independent of magnitude, (2) that within this distance the fluctuations in crustal attenuation properties are negligible countrywide, and (3) that knowing both the depth and the expected epicentral intensity makes it possible to estimate a reliable magnitude.