Preliminary slip rate estimates for the Düzce segment of the North Anatolian Fault Zone from offset geomorphic markers

New estimates on the Quaternary slip rate of the active transform margin of North Anatolia are provided. We investigated the area struck by the 12th November 1999, Mw 7.1 earthquake, that ruptured the Düzce fault segment of the North Anatolian Fault. In order to analyze the spectacular tectonically driven cumulative landforms and the drainage pattern settings, we carried out a 1:25,000-scale geological and geomorphological mapping along the fault trace. We reconstruct and describe, as offset geomorphic markers, right-hand stream deflections and fluvial terraces inset into alluvial fan deposits. Radiocarbon dating indicates that ~100 m stream deflections were built up by the last ~7000 yrs of fault activity. Conversely, two documented and correlated Late Pleistocene fluvial terraces are horizontally offset by ~300 and ~900 m, respectively. These were dated by means of Optically Stimulated Luminescence (OSL) to ~21 ka BP and 60 ka BP. Assuming a constant rate of deformation for the Düzce Fault, ages and related offsets translate to consistent slip-rates that yield an average slip-rate of 15.0 ± 3.2 mm/yr for the last 60 ka. Thus, the Düzce Fault importantly contributes to the North Anatolian margin deformation, suggesting a present-day partitioning of displacement rates with the Mudurnu fault to the south and confirming its important role in the seismic hazard of the area

Probabilistic approach to earthquake prediction.

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

Slip rate of the Düzce segment of the North Anatolian Fault Zone from offset geomorphic markers

We provide new estimates on the Quaternary slip rate of the active transform margin of North Anatolia. We investigated the area struck by 12 November 1999, Mw 7.1 earthquake, that ruptured the Düzce fault segment. In order to analyze the spectacular tectonically driven cumulative landforms and the drainage pattern settings, we carried out a 1:25 000-scale geological and geomorphological map along the fault trace. We reconstruct and describe, as offset geomorphic markers, right-hand stream deflections and remnant of an old alluvial fan modeled by fluvial terraces. The streams are deflected for a total of about 100 m and the onset of the offset was radiocarbon dated about 7000 yr BP. The two documented and correlated Late Pleistocene, terrace risers are offset of about 300 and 890 m, respectively. These terrace risers were dated by means of Optically Stimulated Luminescence (OSL) method about 21 000 yr BP and 60 000 yr BP. These ages and offsets translate to a constant rate of deformation of the Düzce Fault, at different time scales, of 14.0 ± 1.8 mm/yr and disproves a time-variable model at least for the last 60 000 yr. Considering the GPS-measured strain accumulation due to the plate motion along this part of the North Anatolian Fault Zone, the Düzce Fault importantly participates to the North Anatolian margin deformation, suggesting a present-day partitioning of displacement rates with the Mudurnu fault to the south and assuming a relevant role in the seismic hazard of the area

Preface: Marine and Lake Paleoseismology

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Combining inland and offshore paleotsunamis evidence: the Augusta Bay (eastern Sicily, Italy) case study

Offshore and inland geological evidence for multiple tsunami inundations was found in the Augusta Bay area: (1) the main local historical tsunamis (1908, 1693, 1169), (2) two far-generated tsunamis (i.e. Crete 365AD and Santorini, 3600 BP), and (3) seven unknown tsunamis). Average tsunami recurrence intervals from inland and offshore investigations of about 550 and 320 yr, respectively were obtained for the past 4 ka. The history of paleotsunamis from the marine record appears to be as complete as the historical one for the past millennium, yielding an average tsunami recurrence interval of 250 yr for the Augusta Bay. Geological data allow also estimating a minimum tsunami inundation distance of 530m and a minimum run-up of 5 m. The marine record contains evidence for more paleotsunamis with respect to the inland one because of continuous sedimentation and better preservation of stratigraphy in the offshore with respect to coastal areas, which are commonly affected by intermittent-erosion and sedimentation and anthropic activities. This work shows that the integration of geological and historical data can provide critical information regarding the extent and age of tsunamis of the past (e.g. inundation distance, age, and frequency), which is of immediate relevance for tsunami hazard assessment

Slip rate and earthquake recurrence of the Düzce fault (North Anatolian fault zone): integrating geomorphological and paleoseismological analyses

To learn about recurrence of large earthquakes and strain model on the Düzce segment of the North Anatolian Fault Zone, that ruptured on November, 12, 1999 (Mw 7.1), systematic geomorphological and paleoseismological analyses were integrated. In order to provide new estimates on Quaternary slip rate of the fault., geo-morphological mapping along the fault trace permitted to analyze fault-related cumulative landforms and drainage pattern settings. Remnant of an old alluvial fan modeled by fluvial terraces and 41 right-hand stream deflections were reconstructed, described and used as offset geomorphic markers. Two correlated Late Pleistocene, terrace risers, offset of about 300 and 900 m, respectively, were dated by means of OSL method about 21 kyr BP and 60 kyr BP. Moreover, the onset of the offset of the streams deflected for a total of 100 m was radiocarbon dated about 7000 yr BP. These data translate to a constant rate of deformation of 15.0±3.2 mm/yr for the last 60 kyr. On the basis of “characteristic-earthquake model” and under constant slip rate assumptions, it is possible to estimate that stream deflections across the Düzce Fault may be explained by repetition of 20-30 1999-like earthquakes during the last 7000 years, thus the recurrence time for surface rupturing events of the Düzce Fault is 290±60 years. With the aim to reconstruct the record of last large earthquakes, 10 trenches at five sites were excavated. By merging information obtained from all trenches, evidence for three surface faulting earthquakes prior to 1999 were found. These paleoearthquakes are dated on the basis of radiocarbon, 210Pb and archaeological information and can be summarized at: 1) AD1685-1900, possibly end of 19th century; 2) AD1685-1900, possibly close to AD1700; 3) AD800-1000. Some of them can be correlated to historical earthquakes occurred on AD967, 1719, 1878 or 1894. These paleoseismological results, merged with those from previous papers, are suggestive of bimodal recurrence distribution yielding overall average recurrence time of ~350 yrs for the past two millennia, compatible with that calculated from the geomorphic markers analysis. Under the assumption of “characteristic earthquake”, bimodal paleoearthquakes distribution indicate slip rate fluctuations during the past two millennia, with clustered high strain release. These results suggest Wallace-type strain release model for the Düzce fault, and average strain accumulation of 11.4±1.2 mm/yr, in agreement with slip rate results for the past 60 kyr obtained by geomorphic marker analysis

Using geomorphic and biological indicators of coastal uplift for the evaluation of paleoseismicity and

The westernmost part of the Gulf of Corinth (Greece) is an area of very fast extension (~15 mm/yr according to geodetic measurements) and active normal faulting, accompanied by intense coastal uplift and high seismicity. This study presents geomorphic and biological evidence of Holocene coastal uplift at the western extremity of the Gulf, where such evidence was previously unknown. Narrow shore platforms (benches) and rare notches occur mainly on Holocene littoral conglomerates of uplifting small fan deltas. They are perhaps the only primary paleoseismic evidence likely to provide information on earthquake recurrence at coastal faults in the specific part of the Rift system, whereas dated marine fauna can provide constraints on average Holocene coastal uplift rate. The types of geomorphic and biological evidence identified are not ideal, and there are limitations and pitfalls involved in their evaluation. In a first approach, 5 uplifted paleoshorelines may be indentified, at 0.4- 0.7, 1.0-1.3, 1.4-1.7, 2.0-2.3 and 2.8-3.4 m a.m.s.l. They probably formed after 1728 or 2250 Cal. B.P. (depending on the marine reservoir correction used in the calibration of measured radiocarbon ages). A most conservative estimate for the average coastal uplift rate during the Late Holocene is 1.6 or 1.9 mm/yr minimum (with different amounts of reservoir correction). Part of the obtained radiocarbon ages of Lithophaga sp. allows for much higher Holocene uplift rates, of the order of 3-4 mm/yr, which cannot be discarded given that similar figures exist in the bibliography on Holocene and Pleistocene uplift at neighbouring areas. They should best be cross-checked by further studies though. That the identified paleoshoreline record corresponds to episodes of coastal uplift only, cannot be demonstrated beyond all doubt by independent evidence, but it appears the most likely interpretation, given the geological and active-tectonic context and, what is known about eustatic sea-level fluctuations in the Mediterranean. Proving that the documented uplifts were abrupt (i.e., arguably coseismic), is equally difficult, but reasonably expected and rather probable. Five earthquakes in the last ca. 2000 yrs on the coastal fault zone responsible for the uplift, compare well with historical seismicity and the results of recent on-fault paleoseismological studies at the nearby Eliki fault zone. Exact amounts of coseismic uplift cannot be determined precisely, unless the rate of uniform ("regional") non-seismic uplift of Northern Peloponnesus at the specific part of the Corinth Rift is somehow constrained

Geomorphological reconnaissance of the Psathopyrgos and Rion-Patras Fault zones (Achaia, NW Peloponnesus).

Στην εργασία αυτή συζητώνται γεωμορφολογικές παρατηρήσεις κατά μήκος των ενεργών ρηξιγενών ζωνών Ψαθοιτύργου και Ρίου-Πατρών (ΒΑ τμήμα). Οι ρηξιγενείς ζώνες αυτές αντιστοιχούν σε ρηξιγενή μέτωπα περισσότερο ή λιγότερο πολύπλοκης μορφολογίας. Τα γεωμορφολογικά χαρακτηριστικά των μετώπων δίδουν πληροφορίες για την γεωμετρία των ζωνών αυτών, συμπληρωματικές των ήδη υπαρχόντων δεδομένων από γεωλογικές έρευνες. Στοχεύοντας στην αναγνώριση θέσεων δυνητικά κατάλληλων για γεωμορφολογικές και γεωλογικές έρευνες για την εκτίμηση των ρυθμών ολίσθησης ρηγμάτων αυτών των ζωνών κατά το Ολόκαινο, περιγράφονται περιπτώσεις ρηγματωμένων ολοκαινικών γεωμορφών και σχετιζόμενων με αυτές επιφανειακών αποθέσεων. Επι πλέον, συζητώνται τα προβλήματα ανεύρεσης θέσεων κατάλληλων για γεωλογικές/γεωμορφολογικές έρευνες γαι τον χρονικό προσδιορισμό πρόσφατων σεισμικών διαρήξεων (παλαιοσεισμολογία), προβλήματα που οφείλονται τόσο σε ανθρώπινες επεμβάσεις, όσο και σε φυσικές γεωμορφολογικές διεργασίες.In this communication we discuss reconnaissance geomorphological observations along the active Psathopyrgos and Rion-Patras (NE part) fault zones. These fault zones correspond to more or less complex rangefronts, the geomorphic characteristics of which provide hints on the details of the fault zone geometries, adding to the existing geological data in the bibliography. Aiming at the identification of locations suitable or potentially suitable for geomorphological and geological studies for the determination of fault slip rates in the Holocene, we describe cases of faulted Holocene landforms and associated surficial deposits. We also discuss problems involved in finding locations suitable for geological (paleoseismological) studies for the determination of the timing of recent earthquake ruptures, problems due to both man-made and natural causes

Effect of time-dependence on probabilistic seismic hazard maps and deaggregation for the central apennines, Italy

We produce probabilistic seismic hazard assessments for the Central Apennines, Italy, using time-dependent models that are characterized using a Brownian Passage Time (BPT) recurrence model. Using aperiodicity parameters,  of 0.3, 0.5, and 0.7, we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters. For the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults. We use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault (floating fault model) to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation. We show maps for peak ground acceleration (PGA) and 1.0-Hz spectral acceleration (SA1) on rock having 10% probability of exceedence (PE) in 50 years. We produce maps to compare the separate contributions of smoothed seismicity and fault components. In addition we construct maps that show sensitivity of the hazard for different  parameters and the Poisson model. For the Poisson model, the addition of fault sources to the smoothed seismicity raises the hazard by 50 % at locations where the smoothed seismicity contributes the highest hazard, and up to 100 % at locations where the hazard from smoothed seismicity is low. For the strongest aperiodicity parameter (smallest ), the hazard may further increase 60-80 % or more or may decrease by as much as 20 %, depending on the recency of the last event on the fault that dominates the hazard at a given site. In order to present the most likely earthquake magnitude and/or the most likely source-site distance for scenario studies, we deaggregate the seismic hazard for SA1 and PGA for two important cities (Roma and l’Aquila) . For PGA, both locations show the predominance of local sources, having magnitudes of about 5.3 and 6.5 respectively. For SA1 at a site in Rome, there is significant contribution from local smoothed seismicity, and an additional contribution from the more distant Apennine faults having magnitude around 6.8. For l’Aquila, the predominant sources remain local. In order to show the variety of impact of different  values we also obtained deaggregations for another three sites. In general, as  decreases (periodicity increases), the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates. This effect is strongest for the long-period (1 s) ground motions

Geomorphology of the Gubbio Basin (Central Italy): understanding the active tectonics and earthquake potential

The Gubbio Basin is a 22 km long, 4 km wide depression located within the North-Central Apennines fold-andthrust belt. The basin is bounded to the east by the Gubbio Fault, a W-dipping, normal fault dissecting a large Jurassic-Oligocene anticline. Although located along one of the main seismogenic zones of the Peninsula, both historical and instrumental is seismicity is limited with the only exception for the 29 April 1984, Ms 5.3 earthquake, which occurred about 10 km southwest of the basin. Most of the literature attributes this seismicity to the Gubbio Fault. New geomorphic and geologic investigations based on field and aerial photo surveys and DEM analyses provide new insights on the active faulting in the area and are used to infer potential seismogenic sources. Limited evidence of ongoing deformation along the surface expression of the Gubbio Fault was found, possibly because of low rates of deformation versus fast erosional processes. The western side of the basin appears to be controlled by an east-dipping normal fault, antithetic to the Gubbio Fault. Standard dislocation modeling was used to understand the role played by the Gubbio Fault and its antithetic. The Gubbio Fault was divided into a high-angle section above 3.5 km and a low-angle section between 3.5 and 6 km depth. Based on different tests we conclude that both sections of the Gubbio Fault as well as the antitethic fault contributed to the present setting of the basin. At present the antithetic fault appears to be the most effective in producing a geomorphic signature and controlling the basin width. The high-angle Gubbio Fault played a major role in the basin growth but now its activity rate appears minor. Because of the characteristics and location of the 1984 earthquake, the low-angle Gubbio Fault is assumed to be presently active and seismogenic. Based on the integration of geologic, geomorphic and seismological data we suggest that the low-angle Gubbio Fault is formed by two individual sources capable of M 5.3-5.9 earthquakes. The southern source ruptured in the 1984 earthquake while the northern source did not rupture recently nor historically