No abstract

The lack of a well‐recognized relation between large earthquakes and their surface effects in Italy has motivated the detailed reconstruction of the surface expression of the 1980 Campania‐Lucania normal faulting event (Ms = 6.9). Instrumental investigations showed that it was a complex event, composed of four or more subevents occurring within 40 s of the origin time. This earthquake was the first in Italian history, and among the few in the Mediterranean basin, to produce sizable and coherent surface faulting. On the basis of field work we reconstructed three main strands which together form a 38‐km‐long, northwest trending fault scarp. Leveling observations have been used together with field observations to describe the faulting model; geological and geodetic estimates of the focal parameters inferred for each subevent have been compared with similar estimates on the basis of instrumental observations. A good consistency is found between the different models of the 1980 earthquake, with respect to both the magnitude and the geometry of the subevents. The total moment inferred from surface observations is comparable with that computed using long‐period waveform modeling and strong motion accelerograms and is 30% lower than the moment tensor inversion estimate. Much effort has been put into understanding the coseismic deformation‐surface topography interaction. Observations of back‐dipping scarps which tend to reverse the present topography indicate the young age of the presently active tectonic regime. The variability of the surface faulting and the diversion of parts of the scarp from the main trend have been interpreted in terms of intrinsic fragmentation of the characteristic earthquake‐generating 1980 segment; gaps in the scarp height and changes in the fault trend and relation to topography have been identified with persisting “relaxation geometric barriers,” which have been found coincident with the actual rupture initiation sites. The peculiarities of the 1980 earthquake and the youthfulness of its tectonic framework illustrate the first stages of landscape development in a tectonically active region. A correct understanding of this process in well‐monitored regions is essential to recognize long‐term surface features related to large earthquakes of the past and therefore to provide robust estimates for seismic hazard analyses.

Geomorphic and trenching investigations along the Ovindoli-Pezza fault show that this normal fault is one of the major seismogenic faults in the central Apennines. We found clear geological evidence for three Holocene surface-faulting earthquakes on this fault: the most recent earthquake occurred in the Middle Ages between 860 and 1300 A.D., the penultimate occurred about 1900 B.C. or shortly after, and the oldest probably occurred between 3300 and 5000 B.C. Although the most recent surface faulting earthquake occurred during historical time, no evidence for it have been found in the historical record. Slip per event ranges between 2 and 3 m, and the length of the rapture is at least 12-20 km, suggesting M 6.5-7.0 for the palcoearthquakes. The dip-slip rate determined from trenching is 0.7-1.2 mm/yr and is consistent with the long-term slip rate of 0.9-2.5 mm/yr (lower values preferred) obtained from displaced geomorphic features. Trench data combined with long-term slip rate estimates suggest the recurrence interval is longer than a millennium and possibly as long as 3300 years. The time elapsed since the most recent earthquake is 700-1130 years. The seismic behavior of the Ovindoli-Pezza fault is consistent with other well-known seismogenic faults of the central and southern Apennines. The lack of mention or mislocation of the most recent event on the Ovindoli-Pezza fault in the historical record of the past two millennia should be attributed mainly to the unsettled cultural and social conditions and poor economic state that characterized the Middle Ages, especially in thinly populated regions such as the central Apennines. This example highlights an intrinsic limit of the historical data and raises the l•ossibility that other regions considered "seismically quiet" on the basis of a long historical record may in reality have had large earthquakes that were not recorded. quiescent. The Ovindoli-Pezza fault is one of these quiescent segments, yet it shows clear geomorphic Paper number 95JB03213. 0148-022 7/96/9 5JB-03 213 $05.00 evidence for very recent activity [Biasini, 1966; Giraudi, 1989; Cinti et al., 1992]. In contrast, the segments just north and south of the Ovindoli-Pezza fault produced large historical earthquakes: the 1703 L'Aquila earthquake (I = XI Mercalli Cancani Sicberg (MCS) scale [Postpischl, 1985]) and the 1915 Avezzano earthquake (Mw 6.6 [Ward and Valensise, 1989]), respectively. Thus, on the basis of the historical record, the Ovindoli-Pezza fault would either be in a seismic gap or represent a creeping segment of the Apennines seismogenic zone. Because the understanding of the seismogenic processes taking place along the central Apennines is critical to the evaluation of the seismic hazard potential of this region, we studied and trenched the Ovindoli-Pezza fault to reconstruct its seismic history. The importance of this issue is emphasized by the fact that the large historical earthquakes of the central Apennines produced significant damage not only to their epicentral areas but also to the...

The Irpinia fault was the source of the Ms 6.9 1980 Irpinia earthquake and produced the first unequivocal historical surface faulting in Italy. Trenching of the 1980 fault scarp at Piano di Pecore, a flat intermontane basin about 5 km south of the 1980 instrumental epicenter, provides the first data on earthquake recurrence intervals, slip per event, and slip rate on a major normal fault in the Southern Apennines fault zone. The trenches exposed evidence of four pre‐1980 paleoearthquakes that occurred during the past 8600 years. A best estimate average recurrence interval is 2150 years, although the time interval between individual events varies by as much as a factor of 2. Each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation, which suggests that the 1980 event is characteristic for the Irpinia fault. Slip per event values average 61 cm. The net vertical displacement of 2.12–2.36 m since 8600 cal year B.P. observed in the trenches gives a vertical slip rate of 0.25–0.35 mm/yr, a dip slip rate of 0.29–0.40 mm/yr, and an extension rate of 0.14–0.20 mm/yr. Although fault behavior data are only available for the Irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern Apennines. They suggest that (1) fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude (M7) earthquakes and (2) the Holocene rate of extension across the Apennines is ≤1 mm/yr. The 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern Apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation.

The occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century. The large 1908, Messina Straits, blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time‐scale in the order of 100 Kyr. We have compared seismological and geodetic descriptions of the 1908 rupture process with long‐term crustal deformation recorded at different stratigraphic levels by marine terraces, marine sedimentary units, and landscape features. The wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale. We investigated in detail the pattern of deformation of the 125 Kyr‐old, lowest emergent terrace, and found that it mimics the pattern of elevation changes observed following the earthquake. This suggests (1) that the 1908 earthquake is characteristic, (2) that its segment boundaries have been stationary during the past 125 Kyr, and (3) that even the locations of the regions of largest coseismic release do not change through many seismic cycles. Based on a comparison between observed heights of the 125 Kyr terrace and 1908 displacements, we estimated an average repeat time of 1000± yr for a 1908‐type earthquake. We also investigated the height, position, age and state of deformation of older terraces, and found (1) that uplift of the region started about 1 Ma and has since continued rather uniformly at 0.9–1.4 mm yr‐1, (2) that during this time the Straits have narrowed at a rate of 10–20 mm yr‐1, and (3) that all the main geomorphic features of the Messina Straits result from the interaction of fast regional uplift, 1908‐type coseismic subsidence, and global sea‐level fluctuations.

We provide a database of the coseismic geological surface effects following the Mw 6.5 Norcia earthquake that hit central Italy on 30 October 2016. This was one of the strongest seismic events to occur in Europe in the past thirty years, causing complex surface ruptures over an area of >400 km2. The database originated from the collaboration of several European teams (Open EMERGEO Working Group; about 130 researchers) coordinated by the Istituto Nazionale di Geofisica e Vulcanologia. The observations were collected by performing detailed field surveys in the epicentral region in order to describe the geometry and kinematics of surface faulting, and subsequently of landslides and other secondary coseismic effects. The resulting database consists of homogeneous georeferenced records identifying 7323 observation points, each of which contains 18 numeric and string fields of relevant information. This database will impact future earthquake studies focused on modelling of the seismic processes in active extensional settings, updating probabilistic estimates of slip distribution, and assessing the hazard of surface faulting.

No abstract

No abstract