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  • 1
    Publication Date: 2017-04-04
    Description: The November 12, 1999, Mw 7.1 earthquake, ruptured the Düzce segment of the North Anatolian Fault Zone and produced ca. 40 km-long surface ruptures. To learn about recurrence of large surface faulting earthquakes on this fault, we undertook paleoseismological trench investigations. We found evidence for repeated surface faulting paleoearthquakes pre-dating the 1999 event. Dating was based on radiocarbon and 210Pb analyses as well as on archaeological considerations. By merging information obtained from all the trenches we reconstructed the seismic history of the Düzce fault for the past millennium. We correlated coeval events between different trench sites under the assumption that, similarly to the 1999 event, paleoearthquakes ruptured the whole Düzce fault. Besides the 1999 earthquake, prior surface faulting earthquakes are dated as follows: AD1685-1900 (possibly end of 19th century); AD1685-1900 (possibly close to AD 1700); AD1185-1640; AD685-1220 (possibly AD800-1000). Thus, the AD1719, AD1878 and AD1894 historical earthquakes, may have ruptured the Düzce fault and not the faults they are usually associated to or, alternatively, a cascade of events occurred on the Düzce and nearby faults (similarly to the Izmit and Düzce 1999 earthquakes). Five events since AD 685-1220 (possibly AD800-1000), would yield an average recurrence time for the Düzce fault, of 200-325 yr (possibly 250-300 yr). The three most recent earthquakes, including 1999, occurred within 300 yr and may be suggestive of clustering. Assuming that the average 1999 slip is characteristic for this fault, the above recurrence times yield slip rates of 6.7-13.5 mm/yr.
    Description: E.C. project Relief (EVG1-CT-2002-00069)
    Description: Submitted
    Description: open
    Keywords: 1999 Duzce earthquake ; paleoseismicity ; earthquake recurrence ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: manuscript
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  • 2
    Publication Date: 2017-04-04
    Description: The 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 AD1460 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 AD1270–1640), 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.
    Description: Published
    Description: 154-166
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Corinth rift ; normal faults ; paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.03. Geomorphology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2017-04-04
    Description: The November 12, 1999, Mw 7.1 earthquake, ruptured the Düzce segment of the North Anatolian Fault Zone and produced a ca. 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 pre-dating 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: AD1685-1900 (possibly end of 19th century); AD1495-1700; AD685-1020 (possibly AD890-1020). The AD967 and AD1878 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 (AD1495-1700) 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 AD 685-1020 (possibly AD890-1020), would yield an average recurrence time for the Düzce fault of 330-430 yr (possibly 330-370 yr). The three most recent earthquakes, including 1999, occurred within 500 yr. Merging results from other paleoseismological studies along the Düzce fault show a consistency of results and yields average recurrence times for the past 2000 yr of 320-390 yr. 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/yr.
    Description: European Community project RELIEF
    Description: In press
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: open
    Keywords: 1999 earthquake ; North Anatolian Fault ; Paleoearthquakes ; earthquake recurrence ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: manuscript
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  • 4
    Publication Date: 2017-04-04
    Description: 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.
    Description: Published
    Description: B11307
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: partially_open
    Keywords: active fault ; integrated geophysical investigations ; morpho-tectonic analysis ; paleoseismology ; Val d'Agri ; Southern Italy ; 1857 Earthquake ; 04. Solid Earth::04.02. Exploration geophysics::04.02.04. Magnetic and electrical methods ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods ; 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.04. Geology::04.04.11. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
    Publication Date: 2019-11-04
    Description: The evaluation of any earthquake forecast hypothesis requires the application of rigorous statistical methods. It implies a univocal definition of the model characterising the concerned anomaly or precursor, so as it can be objectively recognised in any circumstance and by any observer.A valid forecast hypothesis is expected to maximise successes and minimise false alarms. The probability gain associated to a precursor is also a popular way to estimate the quality of the predictions based on such precursor. Some scientists make use of a statistical approach based on the computation of the likelihood of an observed realisation of seismic events, and on the comparison of the likelihood obtained under different hypotheses. This method can be extended to algorithms that allow the computation of the density distribution of the conditional probability of earthquake occurrence in space, time and magnitude. Whatever method is chosen for building up a new hypothesis, the final assessment of its validity should be carried out by a test on a new and independent set of observations. The implementation of this test could, however, be problematic for seismicity characterised by long-term recurrence intervals. Even using the historical record, that may span time windows extremely variable between a few centuries to a few millennia, we have a low probability to catch more than one or two events on the same fault. Extending the record of earthquakes of the past back in time up to several millennia, paleoseismology represents a great opportunity to study how earthquakes recur through time and thus provide innovative contributions to time-dependent seismic hazard assessment. Sets of paleoseimologically dated earthquakes have been established for some faults in the Mediterranean area: the Irpinia fault in Southern Italy, the Fucino fault in Central Italy, the El Asnam fault in Algeria and the Skinos fault in Central Greece. By using the age of the paleoearthquakes with their associated uncertainty we have computed, through a Montecarlo procedure, the probability that the observed inter-event times come from a uniform random distribution (null hypothesis). This probability is estimated approximately equal to 8.4% for the Irpinia fault, 0.5% for the Fucino fault, 49% for the El Asnam fault and 42% for the Skinos fault. So, the null Poisson hypothesis can be rejected with a confidence level of 99.5% for the Fucino fault, but it can be rejected only with a confidence level between 90% and 95% for the Irpinia fault, while it cannot be rejected for the other two cases. As discussed in the last section of this paper, whatever the scientific value of any prediction hypothesis, it should be considered effective only after evaluation of the balance between the costs and benefits introduced by its practical implementation.
    Description: Published
    Description: JCR Journal
    Description: open
    Keywords: precursors ; earthquake forecast ; statistical tests ; paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 507563 bytes
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