The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with a relief exceeding 2 km. Rock uplift rates of 2-4 mm/a were estimated previously from raised Late Holocene shorelines (Lambeck, 1995) but may not be representative on longer timescales, because earthquakes with up to 9 m of coseismic uplift have recently affected Crete (Stiros, 2001). Here we use marine terraces near Kato Zakros to quantify the long- term rock uplift rate for eastern Crete. Our field investigations and topographic profiles document a flight of at least 15 marine bedrock terraces carved into limestone bedrock. Age constraints for the terraces were obtained by Cl exposure dating of bedrock samples and Be dating of sandstone cobbles found on some terraces. Our results suggest that the terraces T4 and T5 at elevations of 68 and 76 m, respectively, formed during sea level highstands associated with marine isotope stage 5e, i.e. ∼125 ka ago. Correlating the other terraces (T1 to T11) to a sea-level curve for the Red Sea (Siddall et al., 2003) indicates an uplift rate of 0.5-0.6 mm/a during the last 400 ka; significantly lower than previous estimates based on the elevation of Late Holocene shorelines. References Lambeck, K. (1995), Late Pleistocene and Holocene sea-level change in Greece and SW Turkey a separation of eustatic, isostatic and tectonic contributions. Geophys. J. Int. 122, 1022-1044. Siddall, M., Rohling, E.J., Almogi-Labin, A., Hemleben, C., Meischner, D., Schmelzer, I., and Smeed, D.A. (2003), Sea-level fluctuations during the last glacial cycle. Nature, 423, 853-858. Stiros, S.C. (2001), The AD 365 Crete earthquake and possible seismic clustering during the fourth to sixth cen- turies AD in the Eastern Mediterranean: a review of historical and archaeological data. J. Struct. Geol., 23, 545-562.
Terra Nova, 23, 42–48, 2011 Abstract We present denudation rates for catchments in the Qilian Shan and two mountain ranges in its foreland, which differ markedly in elevation and catchment morphology. Catchments with mean slope angles below ∼25° yield 10 Be‐derived denudation rates <∼200 mm ka −1 and have narrow and symmetric slope–frequency distributions, which become broader as the mean slope angle increases. Denudation rates for catchments with mean hillslope angles steeper than ∼25° range from ∼100 to ∼800 mm ka −1 . Field observations suggest that these higher and more variable rates are the result of erosion by bedrock landslides, which contribute to mass transport on the hillslopes. Six catchments aligned along the mountain front of the central Qilian Shan have reached threshold values of slope and relief. These basins also show remarkably similar slope–frequency distributions with negative skewness and a pronounced peak at a slope angle of 30°–35°. We hypothesize that these catchments have attained an erosional steady state.
Abstract. The French Institute for Radiation Protection and Nuclear Safety (IRSN), with the support of the Ministry of Environment, compiled a database (BDFA) to define and characterize known potentially active faults of metropolitan France. The general structure of BDFA is presented in this paper. BDFA reports to date 136 faults and represents a first step toward the implementation of seismic source models that would be used for both deterministic and probabilistic seismic hazard calculations. A robustness index was introduced, highlighting that less than 15 % of the database is controlled by reasonably complete data sets. An example of transposing BDFA into a fault source model for PSHA (probabilistic seismic hazard analysis) calculation is presented for the Upper Rhine Graben (eastern France) and exploited in the companion paper (Chartier et al., 2017, hereafter Part 2) in order to illustrate ongoing challenges for probabilistic fault-based seismic hazard calculations.
Cosmic-ray exposure dating of preserved, seismically exhumed limestone normal fault scarps has been used to identify the last few major earthquakes on seismogenic faults and recover their ages and displacements through the modelling of the content of in situ[36Cl] cosmonuclide of the scarp rocks. However, previous studies neglected some parameters that contribute to 36Cl accumulation and the uncertainties on the inferred earthquake parameters were not discussed. To better constrain earthquake parameters and to explore the limits of this palaeoseismological method, we developed a Matlab® modelling code (provided in Supplementary information) that includes all the factors that may affect [36Cl] observed in seismically exhumed limestone fault scarp rocks. Through a series of synthetic profiles, we examine the effects of each factor on the resulting [36Cl], and quantify the uncertainties related to the variability of those factors. Those most affecting the concentrations are rock composition, site location, shielding resulting from the geometry of the fault scarp and associated colluvium, and scarp denudation. In addition, 36Cl production mechanisms and rates are still being refined, but the importance of these epistemic uncertainties is difficult to assess. We then examine how pre-exposure and exposure histories of fault-zone materials are expressed in [36Cl] profiles. We show that the 36Cl approach allows unambiguous discrimination of sporadic slip versus continuous creep on these faults. It allows identification of the large slip events that have contributed to the scarp exhumation, and provides their displacement with an uncertainty of ±∼25 cm and their age with an uncertainty of ±0.5–1.0 kyr. By contrast, the modelling cannot discriminate whether a slip event is a single event or is composed of multiple events made of temporally clustered smaller size events. As a result, the number of earthquakes identified is always a minimum, while the estimated displacements are maximum bounds and the ages the approximate times when a large earthquake or a cluster of smaller earthquakes have occurred. We applied our approach to a data set available on the Magnola normal fault, Central Italy, including new samples from the buried part of the scarp. Reprocessing of the data helps to refine the seismic history of the fault and quantify the uncertainties in the number of earthquakes, their ages and displacements. We find that the Magnola fault has ruptured during at least five large earthquakes or earthquake clusters in the last 7 ka, and may presently be in a phase of intense activity.
The hypothesis that mountain belts may reach a steady state, in which rock uplift is balanced by erosion, has been supported by numerous field studies and numerical models. The early evolution of mountain ranges, however, and especially the relation between fault growth and topographic response has received little attention. By using a space-for-time substitution we illustrate how active thrust faults and small, fault-bounded mountain ranges evolve into mature mountain chains that will ultimately be incorporated into the laterally growing Tibetan Plateau. At an early stage of development, when faults propagate laterally, slip rates are constant along strike [1-3]. As long as no significant topographic relief has developed, tectonic uplift is at least an order of magnitude faster than the rate of erosion [2,4]. During progressive relief growth and the establishment of drainage basins, erosion of the rising mountain ranges becomes more important, but the studied ranges are still in a pre-steady state and continue to grow both vertically and laterally [5]. During this stage the rate of erosion is linearly correlated to the mean hillslope gradient and the mean local relief, if differences in lithology or rock strength are negligible [6]. The rate of relief growth may be inferred from the difference between local erosion rates on ridge crests and catchment-wide denudation rates [7] – the latter may be taken as a surrogate for the rate of river incision. As hillslopes approach a threshold value, landsliding becomes the dominant process of mass transport and erosion rates increase non-linearly with slope. Once a steady state has been reached, the erosion rate is equal to the rate of rock uplift. A key problem is how the rate of rock uplift can be quantified in such regions, because the stochastic distribution of landslides causes the denudation rates inferred from 10Be in river sediment to be highly variable [8].
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