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...

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S U M M A R YWe studied fault scarps along the northern sector of the Celano-L'Aquila fault system in the Abruzzi region (central Apennines). Up to ∼9.5 km long, 3 m high, fault scarp traces mark the slope foot of ridgetop valleys at Mt Ocre range. In order to provide direct evidence of the deformation history of these scarps, we initiated geomorphic, ground-penetrating radar (GPR) and trenching investigations. GPR investigations yielded subsurface stratigraphic features of the scarp zones, and determined the locations for trenching sites. A total of five trenches were excavated at two different sites. Structural and stratigraphic analysis of the trench exposures combined with historical considerations, showed three faulting events between 5620 BC and 1300 AD; the most recent of them occurred after 1690 BC. Each of these events produced an estimated minimum vertical displacement ranging between 0.3 and 0.5 m. Our interpretation is that the Mt Ocre fault branch represents the northernmost surface expression of a single 35 km long seismogenic structure associated with M ∼ 7 earthquakes. Any attempt to estimate the seismic hazard in the area must consider the presence of this important source.

S U M M A R YLarge historical earthquakes in Italy define a prominent gap in the Pollino region of the southern Apennines. Geomorphic and palaeoseismological investigations in this region show that the Castrovillari fault (CF) is a major seismogenic source that could potentially fill the southern part of this gap. The surface expression of the CF is a complex, 10-13 km long set of prominent scarps. Trenches across one scarp indicate that at least four surface-faulting earthquakes have occurred along the CF since Late Pleistocene time, each producing at least 1 m of vertical displacement. The length of the fault and the slip per event suggest M=6.5-7.0 for the palaeoearthquakes. Preliminary radiocarbon dating coupled with historical considerations imply that the most recent of these earthquakes occurred between 380 BC and 1200 AD, and probably soon after 760 AD; no evidence for this event has been found in the historical record.We estimate a minimum recurrence interval of 1170 years and a vertical slip rate of 0.2-0.5 mm yr-' for the CF, which indicates that the seismic behaviour of this fault is comparable to other major seismogenic faults of the central-southern Apennines. The lack of mention or the mislocation of the most recent event in the historical seismic memory of the Pollino region clearly shows that even in Italy, which has one of the longest historical records of seismicity, a seismic hazard assessment based solely on the historical record may not be completely reliable, and shows that geological investigations are critical for filling possible information gaps.

S U M M A R YThe Eliki fault system dominates the landscape of the southwestern shore of the Gulf of Corinth, where rapid extension rates result in frequent earthquakes. These include an event in 373 BC that destroyed the city of Helike and a recent event in 1861. Uplifted Late Pleistocene marine terraces within the Eastern Eliki Fault footwall suggest revised slip rates of ∼3-5 mm yr −1 , contributing ∼2-3 mm yr −1 geological extension to a net geodetic extension of ∼10-15 mm yr −1 across this part of the rift. Palaeoseismological trenches indicate two and possibly three earthquakes on the Eastern Eliki Fault in the last 1500 yr, including the 1861 earthquake. One trench (EET1A) reveals displaced stratigraphy, but the main fault trace is thought to lie further south beneath the Old National Road. Trench EET1A reveals liquefied sediments associated with an event between AD 1460 and the present, which may be the 1861 event, and displacement during a second event in the interval AD 440-1410 or AD 1270-1640. A third earlier event identified by liquefaction occurred on the Eliki or a nearby fault in AD 440-1410. Using the 1861 and second event (most likely AD 1270-1640), the interval between recent earthquakes is ∼200-600 yr. Suitable trench sites are rare in this region, compounded by human activity over several thousand years. Borehole and trench data indicate that the Kerynites river frequently flowed eastwards along the Eastern Eliki Fault during the last 20-40 kyr, possibly influenced by tectonic tilting from the Eliki and Aigion fault systems and natural channel avulsion.

The 12 November 1999 Mw 7.1 earthquake ruptured the Düzce segment of the North Anatolian Fault Zone and produced a ∼40‐km‐long surface rupture. To improve knowledge about earthquake recurrence on this fault, we undertook paleoseismological trench investigations. We found evidence for repeated surface faulting paleoearthquakes predating the 1999 event during the past millennium. Dating was based on radiocarbon, 210Pb analyses, and archaeological considerations. In addition to the 1999 earthquake, prior surface faulting earthquakes are dated as follows: A.D. 1685–1900 (possibly end of 19th century), A.D. 1495–1700, and A.D. 685–1020 (possibly A.D. 890–1020). The A.D. 967 and A.D. 1878 historical earthquakes are good candidates to have ruptured the Düzce fault correlating with the oldest and penultimate paleoearthquakes. No obvious correlation for the third paleoearthquake (A.D. 1495–1700) exists. These results shows that the Düzce fault considerably participates, along with the parallel Mudurnu fault sections, in the seismogenic deformation taking place along this part of the North Anatolian Fault. Four events since A.D. 685–1020 (possibly A.D. 890–1020) would yield an average recurrence time for the Düzce fault of 330–430 years (possibly 330–370 years). The three most recent earthquakes, including 1999, occurred within 500 years. Merging results from other paleoseismological studies along the Düzce fault show a consistency of results and yields average recurrence times for the past 2000 years of 320–390 years. Assuming that the 1999 slip (2.7 m average, 5 m maximum) is representative of the behavior of this fault, the above recurrence times yield a reference figure of fault slip rate in the range 6.9–15.6 mm/a.

[1] The Southern Apennines range of Italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics, coupled to very recent (Middle Pleistocene) onset and slow slip rates of active normal faults. As shown by the Irpinia Fault, source of a M6.9 earthquake in 1980, major faults might have small cumulative deformation and subtle geomorphic expression. A multidisciplinary study including morphological-tectonic, paleoseismological, and geophysical investigations has been carried out across the extensional Monte Aquila Fault, a poorly known structure that, similarly to the Irpinia Fault, runs across a ridge and is weakly expressed at the surface by small scarps/warps. The joint application of shallow reflection profiling, seismic and electrical resistivity tomography, and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions. Geophysical data clearly (1) image a fault zone beneath suspected warps, (2) constrain the cumulative vertical slip to only 25-30 m, (3) delineate colluvial packages suggesting coseismic surface faulting episodes. Paleoseismological investigations document at least three deformation events during the very Late Pleistocene (<20 ka) and Holocene. The clue to surface-rupturing episodes, together with the fault dimension inferred by geological mapping and microseismicity distribution, suggest a seismogenic potential of M6.3. Our study provides the second documentation of a major active fault in southern Italy that, as the Irpinia Fault, does not bound a large intermontane basin, but it is nested within the mountain range, weakly modifying the landscape. This demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region. More in general, our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques. The proposed multidisciplinary methodology can be effective in regions characterized by young and/or slow slipping active faults.Citation: Improta, L., et al. (2010), Detecting young, slow-slipping active faults by geologic and multidisciplinary highresolution geophysical investigations: A case study from the Apennine seismic belt, Italy,

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