Late Quaternary Uplift Rates Research Articles

Quaternary uplift of palaeoshorelines in southwestern Crete: the combined effect of extensional and compressional faulting

We undertake spatio-temporal analysis on sequences of Pleistocene palaeoshorelines in southwestern Crete where deformed Holocene marine notches have predominantly been suggested to be linked to coseismic uplift from the 365 CE Mw > 8 earthquake. Previous investigations into the Holocene notches have been used to infer that the dominant mechanism of uplift may be slip either on a reverse crustal fault or on the subduction interface. However, seismic reflection studies attest to the presence of numerous active offshore extensional faults whose role in the long-term deformation is unclear. The relative contributions of upper-plate extensional and compressional faults to the overall deformation can be assessed through the study of uplifted and deformed Late Quaternary palaeoshorelines. New 36Cl exposure dating on wave-cut platforms and palaeoshoreline mapping are combined with existing age controls to facilitate investigation into the deformed Late Quaternary palaeoshorelines. We observe that the Late Quaternary uplift rates increase from west (0.61 mm/yr) to east (0.83 mm/yr) over ∼20 km, a spatial uplift pattern that is inconsistent with published vertical deformation models of slip solely on the subduction interface or on a reverse crustal fault. Elastic half-space modelling suggests that an offshore extensional fault may also contribute to the uplift. We conclude that a combination of active extensional and compressional faults may be responsible for Late Quaternary uplift across southwestern Crete.

Late Quaternary neotectonics in the Bird’s Head Peninsula (West Papua), Indonesia: Implications for plate motions in northwestern New Guinea, western Pacific

New Guinea is a mountainous island in a tectonically active setting with regions experiencing rapid uplift rates as shown by the celebrated emergent coral reef terraces of the Huon Peninsula. In the northern Bird’s Head Peninsula of northwestern New Guinea, rapid uplift has been a feature of the tectonic history over the past 2.7 Ma with the development of the mountainous and highly dissected Kemum High (up to 2200 m) associated with the formation of the Central Bird’s Head Monocline, implying a long-term uplift rate approaching 0.8 m/ka. In this work, Late Quaternary uplift rates of up to 1.28 m/ka were determined for emergent coral reefs in the Manokwari region (northeast of the much larger Kemum High). The rapid uplift rates are based on 230Th-U ages (2.7 ± 0.3 to 246.3 ± 8.0 ka with most ages in the range 69–128 ka) on corals and coralline algae, sampled from calcarenites at elevations of 2.45–77.5 m above present sea level. The rapid uplift indicates neotectonic activity reflecting crustal thickening in the Quaternary and neptunian dykes probably related to gravitational instability. The present-day tectonic setting of the Bird’s Head Peninsula is cryptic, but the combination of uplift and tectonic activity shown by the earthquakes are consistent with ongoing oblique convergence between the Bird’s Head and the adjacent Pacific-Caroline plate. Over the past 2 Ma, plate motion between the Bird’s Head Peninsula and the Pacific-Caroline Plate has been accommodated by incipient south-dipping subduction along the Manokwari Trough to the north (with longer-lived subduction along the New Guinea Trench) and sinistral strike-slip movement along the Yapen fault whereas the Sorong Fault has been largely inactive.

Straight from the source's mouth: Controls on field‐constrained sediment export across the entire active Corinth Rift, central Greece

AbstractThe volume and grain‐size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain‐size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain‐sizes of channel bars and full‐weighted grain‐size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain‐size increases westward along the southern coast of the Gulf of Corinth, with the coarse‐fraction grain‐sizes (84th percentile of weighted grain‐size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse‐fraction of the sieved grain‐size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain‐size export is primarily controlled by the input grain‐size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse‐fraction of the grain‐size distribution are predominantly transported in bedload; however, typical sand‐grade particles are transported as suspended load at bankfull conditions, suggesting disparate source‐to‐sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain‐size‐specific bedload discharged into the Gulf of Corinth using the grain‐size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain‐size of sediment export at the rift scale is particularly sensitive to catchment lithology and fluvial mophodynamics, which complicates our ability to make direct inferences of tectonic and palaeoenvironmental forcing from local stratigraphic characteristics.

Late Quaternary sea-level history of Saipan, Commonwealth of the Northern Mariana Islands, USA: A test of tectonic uplift and glacial isostatic adjustment models

Abstract In 1979, S. Uyeda and H. Kanamori proposed a tectonic model with two end members of a subduction-boundary continuum: the “Chilean” type (shallow dip of the subducting plate, great thrust events, compression, and uplift of the overriding plate) and a “Mariana” type (steep dip of the subducting plate, no great thrust events, tension, and no uplift). This concept has been used to explain variable rates of Quaternary uplift around the Pacific Rim, yet no uplift rates have been determined for the Mariana Islands themselves, one of the end members in this model. We studied the late Quaternary Tanapag Limestone, which rims much of the eastern and southern coasts of Saipan, Northern Mariana Islands, with elevations of ∼13 m to ∼30 m. Samples from 12 well-preserved corals (Acropora, Porites, and Goniastrea) yielded U-series ages ranging from ca. 134 ka to ca. 126 ka. These ages correlate the emergent reef of the Tanapag Limestone with the last interglacial period, when sea level was several meters above present. Ages and measured reef elevations from the Tanapag Limestone, along with paleo–sea-level data, yield relatively low late Quaternary uplift rates of 0.002–0.19 m/k.y., consistent with the Uyeda-Kanamori model. A review of data from other localities near subduction zones around the Pacific Basin, however, indicates that many coastlines do not fit the model. Uplift rates along the Chilean coast are predicted to be relatively high, but field studies indicate they are low. On some coastlines, relatively high uplift rates are better explained by subduction of seamounts or submarine ridges rather than subduction zone geometry. Despite the low long-term uplift rate on Saipan, the island also hosts an emergent, low-elevation (+3.9–4.0 m) reef with corals in growth position below a notch (+4.2 m). The corals are dated to 3.9–3.1 ka. The occurrence of this young, emergent reef is likely not due to tectonic uplift; instead, it is interpreted to be the result of glacial isostatic adjustment processes after the end of the last glacial period. Our findings are consistent with similar observations on tectonically stable or slowly uplifting islands elsewhere in the equatorial Pacific Ocean and agree with numerical models of a higher-than-present Holocene sea level in this region due to glacial isostatic adjustment processes.

Sycamore Knoll: A wave-planed pop-up structure in a sinistral-oblique thrust system, Southern California Continental Borderland

At the boundary between the Western Transverse Ranges province and Inner Continental Borderland of Southern California, strain is partitioned across the sinistral-oblique Anacapa-Dume Fault system. Sycamore Knoll, a pop-up structure 20 km west of Point Dume in the hanging wall of the north-dipping Anacapa-Dume Fault, stands out as an anomalous bathymetric high along the Southern California coast. We synthesize new and existing geophysical datasets, including multibeam bathymetry/backscatter and single/multichannel seismic, to understand the morphology and tectonic implications of Sycamore Knoll. We identify a complete eustatic low-stand submerged marine-terrace package encircling Sycamore Knoll platform that corresponds to the Last Glacial Maximum (LGM). The marine-terrace deposits and wave-planed surface of Sycamore Knoll require a late Quaternary uplift rate of 0.55 (+0.5/−0.3) mm/yr relative to sea-level. By combining our uplift rate with previous estimates of basin subsidence and a revised structural model of the Anacapa-Dume Fault, we determine a maximum slip rate in latest Quaternary time of 1.50 (+0.5/−0.3) mm/yr and hence a post-LGM rate of convergence across the Anacapa-Dume Fault of 0.60 (+0.2/−0.1) mm/yr.

Late Quaternary uplift rate inferred from marine terraces, Muroto Peninsula, southwest Japan: Forearc deformation in an oblique subduction zone

Tectonic uplift rates across the Muroto Peninsula, in the southwest Japan forearc (the overriding plate in the southwest Japan oblique subduction zone), were estimated by mapping the elevations of the inner edges of marine terrace surfaces. The uplift rates inferred from marine terraces M1 and M2, which were correlated by tephrochronology with marine isotope stages (MIS) 5e and 5c, respectively, include some vertical offset by local faults but generally decrease northwestward from 1.2–1.6mky−1 on Cape Muroto to 0.3–0.7mky−1 in the Kochi Plain. The vertical deformation of the Muroto Peninsula since MIS 5e and 5c was interpreted as a combination of regional uplift and folding related to the arc-normal offshore Muroto–Misaki fault. A regional uplift rate of 0.46mky−1 was estimated from terraces on the Muroto Peninsula, and the residual deformation of these terraces was attributed to fault-related folding. A mass-balance calculation yielded a shortening rate of 0.71–0.77mky−1 for the Muroto Peninsula, with the Muroto–Misaki fault accounting for 0.60–0.71mky−1, but these rates may be overestimated by as much as 10% given variations of several meters in the elevation difference between the buried shoreline angles and terrace inner edges in the study area. A thrust fault model with flat (5–10° dip) and ramp (60° dip) components is proposed to explain the shortening rate and uplift rate of the Muroto–Misaki fault since MIS 5e. Bedrock deformation also indicates that the northern extension of this fault corresponds to the older Muroto Flexure.

Landscape response to tectonic and climatic forcing in the foredeep of the southern Apennines, Italy: insights from Quaternary stratigraphy, quantitative geomorphic analysis, and denudation rate proxies

ABSTRACTWe present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the Tavoliere di Puglia plain, a low‐relief landscape representing the northernmost sector of the Pliocene‐Pleistocene foredeep of the southern Apennines. The study area is located between the easternmost part of the southern Apennine chain and the Gargano promontory and it is characterized by several orders of terraced fluvial deposits, disconformably overlying lower Pleistocene marine clay and organized in a staircase geometry, which recorded the emersion and the long‐term incision history of this sector since mid‐Pleistocene times. We used the spatial and altimetric distribution of several orders of middle to late Pleistocene fluvial terraces in order to perform paleotopographic reconstruction and GIS‐aided eroded volumes estimates. Then, we estimated denudation rates on the basis of the terraces chronostratigraphy, supported by published OSL and AAR dating. Middle to upper Pleistocene denudation rates estimated by means of such an approach are slightly lower than 0.1 mm yr‐1, in good agreement with short‐term data from direct and indirect evaluation of suspended sediment yield. The analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area. Middle to late Quaternary uplift rates (about 0.15 mm yr‐1), calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area, are quite similar to the erosion rates average value, thus suggesting a steady‐state fluvial incision. The approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and ksn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady‐state equilibrium. Copyright © 2014 John Wiley & Sons, Ltd.

Late Quaternary uplift rate inferred from marine terraces, Shimokita Peninsula, northeastern Japan: A preliminary investigation of the buried shoreline angle

After estimating tectonic uplift rates along the northern part of the northeast Japan forearc (the overriding plate in the northeast Japan subduction zone) by mapping the elevation of the inner edges of marine terrace surfaces, we refined this estimate through elevation measurements of the buried shoreline angle beneath well-dated marine terrace surfaces, from which we could derive more accurate paleo-sea levels. The uplift rate initially inferred from the inner edge of marine terrace T4, correlated with marine isotope stage MIS 5e by tephrochronology, increases eastward from 0.11–0.22mky−1 around the backarc volcanic front to 0.17–0.32mky−1 in the forearc on the peninsula of Shiriyazaki. We refined the uplift rates for T4, on the basis of the shoreline angle elevation, from the reconstructed profile of the paleo-sea cliff and wave-cut platform on a rocky coast and the reconstructed profile of the swash zone sediments and terrace deposits on a sandy coast. The refined uplift rates were 0.14–0.25mky−1 on the rocky coast and 0.14–0.23mky−1 on the sandy coast, slightly slower than the rates we inferred from the height of T4 and about one-half to three-fourths of previously reported rates. By extrapolation from the example of the sandy coast, the refined uplift rate around the volcanic front was 0.09–0.18mky−1. The vertical deformation across the forearc of the Shimokita Peninsula since MIS 5e is possibly associated with regional isostatic uplift of 0.09–0.18mky−1 and anticlinal deformation by an offshore fault, interpreted from acoustic profiles, of 0.05–0.07mky−1.

Upper-plate deformation in response to flat slab subduction inboard of the aseismic Cocos Ridge, Osa Peninsula, Costa Rica

Along the Middle America Trench in southern Costa Rica, flat slab subduction of the aseismic Cocos Ridge has uplifted and exposed the outer forearc, shortened the Terraba forearc basin sequence in the inner forearc (i.e., the Fila Costena thrust belt), and uplifted the magmatic arc. The Osa Peninsula, an outer forearc high ∼20 km inboard of the Middle America Trench and ∼3 km to ∼10 km above the plate interface at its trenchward edge, is deforming in response to variations in the bathymetry of the subducting aseismic Cocos Ridge where relief locally exceeds 1 km. Modern topography of the Osa Peninsula, elevation of the basement rocks (Early to Middle Tertiary Osa melange), elevations of Quaternary marine deposits (Marenco formation), and distribution of late Quaternary uplift rates directly mirror the bathymetry on the Cocos Ridge outboard of the Middle America Trench. Rates of late Quaternary uplift are calculated from eight new radiocarbon ages, five new optically stimulated luminescence ages, and 10 previously published radiocarbon ages. Rates of uplift range from 1.7 m/k.y. to 8.5 m/k.y. The Osa Peninsula is fragmented into small (∼5 km), independently deforming blocks bounded by trench-parallel and trench-perpendicular, subvertical, normal and reverse faults that extend down to the plate interface, allowing for greatly different deformation histories over short distances. Quaternary deformation on the Osa Peninsula is modeled as a thin, outer-margin wedge that deforms in response to subduction of short-wavelength, high-relief asperities on the downgoing plate. Permanent deformation is largely accomplished by simple shear on a complex array of subvertical faults that allow the upper plate to adjust to variations in the slope of incoming ridges and seamounts. Currently, permanent deformation of the outer forearc does not appear to involve significant subhorizontal shortening of the margin wedge, although the global positioning system velocity field records elastic shortening related to locking of the plate interface. Permanent uplift and uplift rates in the outer forearc in southern Costa Rica are driven, to the first order, by the bathymetry associated with the subducting Cocos Ridge and not by the basal shear stress on the plate interface.

Sea-level history of past interglacial periods from uranium-series dating of corals, Curaçao, Leeward Antilles islands

Curaçao has reef terraces with the potential to provide sea-level histories of interglacial periods. Ages of the Hato (upper) unit of the “Lower Terrace” indicate that this reef dates to the last interglacial period, Marine Isotope Stage (MIS) 5.5. On Curaçao, this high sea stand lasted at least 8000yr (~126 to ~118ka). Elevations and age of this reef show that late Quaternary uplift rates on Curaçao are low, 0.026–0.054m/ka, consistent with its tectonic setting. Ages of ~200ka for corals from the older Cortalein unit of the Lower Terrace correlate this reef to MIS 7, with paleo-sea level estimates ranging from −3.3m to +2.3m. The estimates are in agreement with those for MIS 7 made from other localities and indicate that the penultimate interglacial period was a time of significant warmth, on a par with the present interglacial period. The ~400ka (MIS 11) Middle Terrace I on Curaçao, dated by others, may have formed from a paleo-sea level of +8.3 to +10.0m, or (less likely) +17m to +20m. The lower estimates are conservative compared to previous studies, but still require major ice sheet loss from Greenland and Antarctica.

Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

San Nicolas Island, California has one of the best records of fossiliferous Quaternary marine terraces in North America, with at least fourteen terraces rising to an elevation of ∼270 m above present-day sea level. In our studies of the lowest terraces, we identified platforms at 38–36 m (terrace 2a), 33–28 m (terrace 2b), and 13–8 m (terrace 1). Uranium-series dating of solitary corals from these terraces yields three clusters of ages: ∼120 ka on terrace 2a (marine isotope stage [MIS] 5.5), ∼120 and ∼100 ka on terrace 2b (MIS 5.5 and 5.3), and ∼80 ka (MIS 5.1) on terrace 1. We conclude that corals on terrace 2b that date to ∼120 ka were reworked from a formerly broader terrace 2a during the ∼100 ka sea stand. Fossil faunas differ on the three terraces. Isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding San Nicolas Island. A mix of extralimital southern and extralimital northern species is found on terrace 2b, and extralimital northern species are on terrace 1. On terrace 2b, with its mixed faunas, extralimital southern species, indicating warmer than present waters, are interpreted to be from the ∼120 ka high sea stand, reworked from terrace 2a. The extralimital northern species on terrace 2b, indicating cooler than present waters, are interpreted to be from the ∼100 ka sea stand. The abundant extralimital northern species on terrace 1 indicate cooler than present waters at ∼80 ka.Using the highest elevations of the ∼120 ka platform of terrace 2a, and assuming a paleo-sea level of +6 m based on previous studies, San Nicolas Island has experienced late Quaternary uplift rates of ∼0.25–0.27 m/ka. These uplift rates, along with shoreline angle elevations and ages of terrace 2b (∼100 ka) and terrace 1 (∼80 ka) yield relative (local) paleo-sea level elevations of +2 to +6 m for the ∼100 ka sea stand and −11 to −12 m for the ∼80 ka sea stand. These estimates are significantly higher than those reported for the ∼100 ka and ∼80 ka sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure.

Late Quaternary high uplift rates in northeastern Sicily: evidence from calcareous nannofossils and benthic and planktonic foraminifera

The northeastern part of Sicily is characterized by intense seismic activity. Several systems of faults have been recognized in Pliocene and Pleistocene sediments in the area and, in fact, estimates of uplift rates are among the highest recorded in Sicily and south Italy. We examined calcareous nannofossil and benthic and planktonic foraminifera assemblages from pelitic sediments of the Contrada Zura section (Barcellona Pozzo di Gotto Basin, Furnari village, Messina). The occurrence of Emiliania huxleyi, a coccolithophore species which appeared in the oceanic record about 270,000 years ago, is witness to the uniqueness of this outcrop, while the planktonic/benthic foraminifera ratio indicates a deep (slope) environment, in agreement with previous observations on macrobenthic and ostracod paleo-communities. Independently from the numerical estimate of the paleo-depth, there is little doubt that the occurrence of E. huxleyi in such sediments might be explained by exceptional uplift rates. Since resulting uplift rate estimates, between 3.2 and 5.5 mm/year, exceeded by far the regional, longer-term, vertical tectonic motion, we argue that a major contribution of coseismic displacement along active faults occurred in the Furnari area.

Late Quaternary and coseismic crustal deformation across the focal area of the 2008 Iwate–Miyagi Nairiku earthquake

We investigated late Quaternary and coseismic crustal deformation rates in the 2008 Iwate–Miyagi Nairiku earthquake (2008 IMEQ) focal area. We identified five fluvial terraces and used tephrochronology and 14C dating to correlate them with marine isotope stages (MISs) 6–5, slightly younger than 5.3–5.2, 4–5, 2–1, and 1. The late Quaternary uplift rates calculated from the relative heights of the MIS 6–5 (120–140 ka) and 2–1 (10 ka) terrace surfaces were 0.18–0.21 ± 0.13 m/ky and 0.62–0.74 ± 0.13 m/ky on the downthrown and upthrown sides of the 2008 IMEQ fault, respectively. We developed a fault model that reflected the coseismic vertical displacements and surface ruptures. This model had a fault plane dipping to the west at 40° with slip of 4.4 m on the deep (10–3 km depth) part of the fault plane and of 0.3 m on the shallow (3–0 km depth) part. The late Quaternary and coseismic deformation pattern of the ground surface roughly agree. Furthermore, the recurrence interval (2.9–4.2 ky) calculated from the late Quaternary vertical offset and coseismic vertical deformation roughly agrees with the findings of a previous trenching study. Thus, the slip on the fault of the 2008 IMEQ was a characteristic earthquake event.

Late Quaternary uplift rate of the northeastern Japan arc inferred from fluvial terraces

Crustal uplift rates of the Isawa upland in the central part of the northeastern Japan forearc are estimated using the height distribution of late Quaternary fluvial terraces. The ages of fluvial terraces are correlated to marine isotope stages (MISs) by tephrochronology and 14C dating. The latest and older fill terrace surfaces were correlated to MIS 2/1 and MIS 6/5, respectively. The incision rate, estimated as 0.15–0.19 ± 0.07 m ky − 1 from the relative heights of the fill terrace surfaces, agrees roughly with the uplift rate along the Pacific coast (0.14–0.23 m ky − 1 ) determined from an MIS 5.5 marine terrace surface. In contrast, geodetic surveys (leveling surveys) and GPS observations show that the forearc is currently subsiding at a maximum rate of 5.6 mm y − 1 . Thus, the current geodetic subsidence does not reflect long-term (geological) tectonic movement. Vertical deformation of the northeastern Japan forearc is unique in terms of its direction and rate, as a deformation process of an overriding plate in an erosion-dominant subduction zone.

Dating topographic evolution in New Zealand using mitochondrial DNA

Tectonic processes and/or climate-related fluvial activity commonly cause river drainage reorientation that can affect topographic development and sedimentary depocentres on a regional scale. Drainage reorientation results from development of a physical barrier within a river valley, erosional river capture, or a combination of these. Physical barriers also separate indigenous freshwater fish, resulting in isolated populations that then evolve independently. Divergent molecular evolution of mitochondrial DNA in the separated populations results in measurable differences in DNA sequences after about 5-10 ka. We are calibrating the resultant “molecular clock” using suitable geological barrierforming events associated with glacial and tectonic development of topography in the South Island of New Zealand. Several Holocene and late Quaternary glacial outwash and tectonic barriers have been dated by regional fluvial terrace correlation supplemented by carbon dating [1]. A middle Quaternary tectonic barrier has been dated by extrapolation of late Quaternary uplift rate estimates [2].The age of an early Quaternary barrier has been estimated from Be and Al dating of surface materials [3]. The resultant calibration line implies DNA divergence rates of about 10%/Ma, which is substantially faster than longer-term DNA divergence rates commonly used by biologists (typically about 2%/Ma). Further work is needed to determine if the divergence rate is linear through the Quaternary, but the method shows promise as a potential dating tool for Quaternary topographic evolution events. This method is useful in active tectonic settings where the rate of geomorphic evolution is similar to the rate of biological evolution. The method dates the last time that a “wet connection” existed between drainages that allowed genetic interchange between now-separated populations.

Quantification of Quaternary vertical movements in the central Pannonian Basin: A review of chronologic data along the Danube River, Hungary

This study aims at a new quantification of neotectonic deformation of the central part of the Pannonian Basin. We use terrace levels and associated travertine as well as speleothem data along the Danube River to quantify its incision rate and thus, estimate the amount and rate of uplift at the axis of the Hungarian Mountain Range (HMR). Several terrace levels and other geomorphic features along the Danube river are indicative for Quaternary uplift of the axial part of the emerging Hungarian Mountain Range. While the correlative terraces are at considerable height at the axis of the HMR, the terraces are gradually dipping below the basin fill of the adjacent lowlands. The correlation of the terrace segments is difficult because of their poor preservation, small size and variable height. The geomorphologic horizons indicate gradual incision of the river throughout the Quaternary during simultaneous deformation. However, no reliable chronological data have been available so far to quantify landscape-forming processes such as uplift, incision or erosion rates. A reconsideration of existing published data for three consecutive segments of the Danube valley yields incision rates between 0.14 and 0.41 mm/year for the last 360 ky, with the highest value for the area of the Danube Bend. Accordingly, the middle to late Quaternary uplift rate of the axial zone of the HMR exceeded significantly that of the marginal areas. These rates represent an approximation as some quantitative data are still controversial. Our results suggest that formation of the Danube terraces is result of river incision triggered by the uplift of the HMR and modified by periodic climate changes.

Coastal Tectonics across the South Atlas Thrust Front and the Agadir Active Zone, Morocco

Abstract Quaternary marine terraces of the South Atlas Thrust Front near the Agadir seismogenic region are investigated by detailed geological mapping, precise height measurement and tectonic analysis. A coastal step-like morphology with four main benches (Q 1 -Q 4 ) crosses the Ait Lamine-Kasbah anticlines, 10 km north of Agadir. U-Th dating of 12 fossil samples (mainly molluscs) yields two main groups of ages for marine terraces Q 4 and Q 3 and can be correlated with oxygen-isotope stages 5 and 7 respectively. Terrace height changes significantly near the Kasbah fold, and attains a maximum of 18–28 m for Q 4 and 35.5 m for Q 3 . Estimates and measurements of terrace elevation yield an average late Quaternary uplift rate of 0.1–0.2 mm/year. Modelling of anticlinal structures suggests that the Kasbah fold may have developed as a fault-propagation fold with a low dip angle of 25° or a listric geometry as implied by flexural slip faulting. Surface ruptures associated with the 1960 ( M s 5.9) earthquake coincide with flexural slip faulting showing 4–5 m offset of terrace Q 3 . Incremental movements and uplifted marine terraces on the Kasbah fold are likely to occur during large earthquakes related to the 25 km long flexural slip fault.

Earthquake‐induced flooding and paleoseismicity of the El Asnam, Algeria, fault‐related fold

Late Quaternary activity of the El Asnam thrust fault (responsible for the October 10, 1980, MS = 7.3 earthquake and 36‐km coseismic faulting) is explored through diverse paleoseismological field methods. We trenched through the main and secondary 1980 coseismic scarps, made an analysis of earthquake‐induced flood deposits, conducted a geomorphic study of leveling profiles and offset geological units across thrust and normal scarps, and considered the geomorphology of the active fold. Twenty‐five radiocarbon ages from colluvial and alluvial deposits, along with conventional (fossils and artefacts) dating of geological units, show the timing of successive net vertical displacements on the thrust‐related fold and bending‐moment faults. Previous work showed that eight pre‐1980 earthquakes occurred in clusters during the late Holocene. Cumulative net vertical slip that amounts to 3 times the 1980 displacement is observed on multiple thrust fault scarps and offsets of geological units on bending‐moment faults. Maximum cumulative vertical displacements, which are visible in different zones along the fault segments, can reach 10 to 25 times the 1980 coseismic displacements. The late Quaternary uplift rate on the El Asnam fault is 0.6 mm/yr, and taking into account slip variation along the fault, this rate may range between 0.25 – 1.6 mm/yr, from which we obtain a shortening rate of 0.17 – 1.2 mm/yr. Because the Tell Atlas mountains exhibit comparable seismogenic fault‐related folds with parallel and sequential structures of active faults, a total average shortening rate of 2.05 mm/yr during the late Quaternary represents part of the convergence accommodated along the Africa‐Eurasia plate boundary.

Late quaternary uplift rates of marine terraces on the Pacific coast of North America, southern Oregon to Baja California sur

Marine terraces are common landforms along the Pacific coast of North America from southern Oregon to southern Baja California. We report 60 new uranium-series ages of marine terrace corals, hydrocorals, and other fossils. Terraces representing the ca. 80 ka and ca. 125 ka high stands of sea are the most common along the Pacific coast and we have used these ages, along with terrace shoreline angle elevations and paleo-sea-level estimates, to calculate Late Quaternary uplift rates. Uplift rates in the forearc region of the Cascadia subduction zone range from 0.45–1.08 m/kyr. Farther south, along most of the coast west of the San Andreas fault zone, uplift rates range from 0.15–0.35 m/kyr, but some areas have significantly higher rates of uplift and others have apparently experienced little or no uplift in the last 125 ka. In Baja California Sur, west of the East Pacific Rise, little or no uplift has occurred during the Late Quaternary. On average, the magnitude of rates of uplift for the tectonic regimes is as follows: Cascadia subduction zone > San Andreas fault zone region > East Pacific Rise region.

Age estimates and uplift rates for Late Pleistocene marine terraces: Southern Oregon portion of the Cascadia Forearc

Marine terraces are prominent landforms along the southern Oregon coast, which forms part of the forearc region of the Cascadia subduction zone. Interest in the Cascadia subduction zone has increased because recent investigations have suggested that slip along plates at certain types of convergent margins is characteristically accompanied by large earthquakes. In addition, other investigations have suggested that convergent margins can be broadly classified by the magnitude of their uplift rates. With these hypotheses in mind, we generated new uranium series, amino acid, and stable isotope data for southern Oregon marine terrace fossils. These data, along with terrace elevations and two alternative estimates of sea level at the time of terrace formation, allow us to determine terrace ages and uplift rates. Uranium series analysis of fossil coral yields an age of 83±5 ka for the Whisky Run terrace at Coquille Point in Bandon, Oregon. A combination of amino acid and oxygen isotope data suggest ages of about 80 and 105 ka for the lowest two terraces at Cape Blanco. These ages indicate uplift rates of 0.45–1.05 and 0.81–1.49 m/kyr for Coquille Point and Cape Blanco, respectively. Late Quaternary uplift rates of marine terraces yield information about deformation in the overriding plate, but it is unclear if such data vary systematically with convergent margin type. In order to assess the utility of the southern Oregon uplift rates for predicting the behavior of the Cascadia subduction zone, we compared late Quaternary uplift rates derived from terrace data from subduction zones around the world. On the basis of this comparison the southern Oregon rates of vertical deformation are not unusually high or low. Furthermore, late Quaternary uplift rates show little relationship to the type of convergent margin. These observations suggest that local structures may play a large role in uplift rate variability. In addition, while the type of convergent margin may place an upper limit on possible uplift rate, greater upper limits serve to increase the range of possible uplift rates. In the case of the southern Oregon coast, variability in uplift rate probably reflects local structures in the overriding plate, and the rate of uplift cannot be used as a simple index of the potential for great earthquakes along the southern Cascadia subduction zone.