Terrace Risers Research Articles

Surface Ruptures Associated with the 1937 M 7.5 Tuosuo Lake and the 1963 M 7.0 Alake Lake Earthquakes and the Paleoseismicity along the Tuosuo Lake Segment of the Kunlun Fault, Northern Tibet

Examination of aerial photos taken in the late 1960s and field mapping allowed us to re-evaluate the surface ruptures associated with the 1937 M 7.5 Tuosuo Lake and 1963 M 7.0 Alake Lake earthquakes along the Tuosuo Lake and Alake Lake segments, central part of the Kunlun fault. Individual ruptures can be distinguished by their freshness of surface expression, slip distributions, and surficial geometry; they are separated by the geometrical bend that probably acts as an effective barrier to rupture propagation of these earthquakes. The rupture (∼40 km long with 1–2 m left-lateral slip) of the 1963 Alake Lake earthquake occurred on the west of the bend, whereas that of the 1937 Tuosuo Lake earthquake (about 150 km long with 4.1 m mean left-lateral offset) occurred on the east of the bend. The change of dip- slip sense reflects the characteristics of jogs and bends along the segment boundaries. Systematically and progressively displaced terrace risers and gullies indicate repeated activity of the fault during the late Quaternary. Five trenches excavated across the surface ruptures along the Tuosuo Lake segment reveal distinct indicators of paleoseismic events. At least nine earthquakes are constrained in the Holocene deposits, and a 630 ± 130 yr, upper-bound recurrence interval of large earthquakes in the past 2000 years is determined.

Slip rate gradients along the eastern Kunlun fault

Whether strike‐slip fault systems in Eurasia accomplish eastward extrusion of Tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip. Here we present new slip rate determinations using millennial‐scale geomorphic markers from sites along the easternmost segment of the Kunlun fault in north central Tibet. This fault system represents one of the major strike‐slip faults within the Indo‐Asian collision zone, has been argued to exhibit uniform slip rates along much of its length, and plays a central role in models for eastward extrusion of Tibetan lithosphere. Displaced fluvial terrace risers along tributaries of the Yellow River, coupled with14C ages of terrace material, provide constraints on slip rates over late Pleistocene to Holocene time. Results indicate that slip rates decrease systematically along the eastern ∼150 km of the fault from >10 to <2 mm/yr. These data challenge the view that slip along the Kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips. Moreover, slip along the fault appears to terminate within the thickened crust of the plateau, and therefore any extrusion of Tibetan lithosphere accomplished by slip along the Kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip.

Nutrient losses from rain‐fed bench terraced cultivation systems in high rainfall areas of the mid‐hills of Nepal

AbstractBetween the elevations of 1000 and 2000 m in the mid‐hills of Nepal, over 12 million people subsist on land‐holdings of less than 0·5 ha. These farmers have limited access to commercial inputs such as fertilisers and are reliant on organic manures for soil fertility maintenance. Participatory research was conducted with farmers on bari land (upper slope rain‐fed crop terraces) in the hill community of Landruk (bench terraces 0–5° slope, 3000–3500 mm annual rainfall, which aimed to develop soil and water management interventions that controlled erosion without resulting in high leaching, and so were effective in minimising total nutrient losses. Interventions tested were the control of water movement through diversion of run‐on and planting fodder grasses on terrace risers on bench terraces. The interventions were effective in reducing soil loss from the bari land in comparison with existing farmer practices, but no effect was observed on nutrient losses in solution form through runoff and leaching. Losses of NO3‐N in leachate ranged from 17·3 to 99·7 kg ha−1 yr−1, but only 0·7 to 5·6 kg ha−1 yr−1 in runoff. The overall nutrient balance suggests that the system is not sustainable. Fertility is heavily dependent on livestock inputs and if the current trends of declining livestock numbers due to labour constraints continue, further losses in productivity can be expected. However, farmers are interested in interventions that tie ecosystem services with productivity enhancement and farmers' priorities should be used as entry points for promoting interventions that are system compatible and harness niche opportunities. Copyright © 2007 John Wiley & Sons, Ltd.

Rates of active faulting during late Quaternary fluvial terrace formation at Saxton River, Awatere fault, New Zealand

A flight of faulted fluvial terraces at Saxton River on the Awatere fault, northeast South Island, New Zealand, preserves the incremental slip history and detailed paleoearthquake chronology of this major strike-slip fault. Here, six fluvial terraces have been progressively displaced across the inland Molesworth section of the fault, with horizontal displacements ranging from -6 m for an ephemeral channel on the youngest terrace to 81 m for the riser above the oldest terrace. New optically stimulated luminescence ages for abandonment of the two oldest terrace treads are 14.5 ± 1.5 and 6.7 ± 0.7 ka. When combined with new measurements of incremental horizontal displacements and previous age data, these new ages indicate that strike-slip on this part of the Awatere fault has been occurring at a near-constant rate of 5.6 ± 0.8 mm/yr since ca. 15 ka. This rate is similar to recent slip-rate estimates for an adjoining section of the same fault to the east, which suggests that | there is near-complete slip transfer across the junction between the two fault strands. Comparison of the magnitudes and ages of the terrace riser displacements to the timing of paleoearthquakes on the Molesworth section allows the mean per event horizontal displacement over the eight most recent surface-rupture events to be estimated at 4.4 ± 0.8 m. Between ca. 5 ka and ca. 2 ka, surface-rupturing earthquakes increased in frequency and decreased in their mean coseismic displacements to <2.6 m. During this time, the sense of local dip slip also shifted from north-side-up to south-side-up. Rapid incision of Saxton River in the mid-Holocene may have caused a perturbation in the near-surface stress directions acting on the fault plane beneath the Saxton River valley, forcing a change in the near-surface fault geometry that resulted in the shift in sense of dip slip.

Soft-riser bench terrace design for the hilly loess region of Shaanxi Province, China

Reconfiguration of hillside fields into terraces is regarded as one of the key techniques for water and soil conservation in mountainous regions. On slopes exceeding 75°, traditional techniques of terracing are difficult to apply as terrace risers (i.e. backslopes), if not reinforced, are so abrupt that they collapse under gravity alone, thus damaging the terrace. To improve reconfiguring of hillside fields into terraces, holistic techniques of soft-riser bench terrace engineering, including revegetation with trees and planting of grasses on terrace riser slopes, were tested between 1997 and 2001 in Xiabiabgou watershed, Yan’an, Shaanxi Province, China. A “working with nature” engineering approach was employed, terrace riser slopes of 45°, similar to the pre-existing slope of 35°, were employed to reduce gravity erosion radically. Based on concepts of biodiversity and principles of landscape ecology, terrace benches, bunds and risers were planted with trees, shrubs, forage grasses, and crops, serving to generate a diverse array of plants, a semi-forested area and to stabilize terrace bunds and risers. Soft-riser bench terrace design made it possible to reduce hazards arising from gravity erosion significantly, and reduce the costs of individual terrace riser construction and maintenance to 73.93% and 49.68%, respectively, of costs under traditional techniques. Such a construction allowed an enrichment and concentration of nutrients in the soil of the terrace bunds and risers, providing an ideal environment for a range of plants to grow and develop. The terrace riser can be planted with a drought-resistant plants ranging from forage grasses to trees. This terrace riser vegetation will turn the exposed terrace bunds and risers existing under traditional techniques into plant-covered belts, great green ribbons decorating the farmland, and contributing to the enhancement of the landscape's biology.

Sustainability of modern land terracing for vineyard plantation in a Mediterranean mountain environment – The case of the Priorat region (NE Spain)

Vineyard restructuring in the Priorat region of NE Spain has transformed both traditional vineyards and abandoned cultivated hillslopes into mechanized vineyards. These new terraced vineyards do not look sustainable under existing environmental conditions. A survey assessing the terrace design of the new mechanized vineyards was initiated a few months after crop establishment. Using a Geodimeter total station, vertical and horizontal intervals between the terraces and the slope of the terrace risers were measured. The results were then compared to accepted terrace design criteria. Additionally, the magnitudes and locations of soil movement that occurred on the risers after vineyard establishment were surveyed. Vineyard infrastructure and vines affected by mass movements as well as rainfall characteristics were also evaluated. The results indicate that the modern terraces are unstable and may lead to a degraded environmental situation. The only factor considered by farmers at the time of the terrace construction is trafficability, i.e., the width suitable for machinery movement. Therefore, the terraces have riser heights (4.8 ± 3.0 m) and widths (6.2 ± 3.5 m) greater than accepted design criteria for the steep conditions in the study area. Indeed, one extreme rainfall event shortly after the terrace construction induced landslides which affected 4950 m 2. About 75% of the area affected by the mass movements occur in the lower third of the slopes, where 6.9% of the plants, irrigation and training systems were damaged.

Geomorphic Controls of Spatial Pattern and Process at Alpine Treeline*

This study examines the role of surface geomorphic features in tree establishment at the alpine treeline in Glacier National Park, Montana, through the presentation of a multiscale, conceptual model of biogeomorphic relationships at alpine treeline. Empirical observations gathered through a multiscale field methodology over three summers serve as a base for the model. The model highlights the importance of surface geomorphic features, specifically boulders and terrace risers, in creating favorable local site conditions, largely by protecting seedlings from wind. The sheltering effect of surface features enables initial seedling establishment, and in some cases survival, above current treeline locations, thereby initiating a positive feedback effect that encourages subsequent tree establishment. Geomorphic features are therefore important in linking scales of pattern and process at the alpine treeline ecotone.

New Constraints on Recent Large Earthquakes along the Xidatan-Dongdatan Segment of the Kunlun Fault, Western China

Field investigation and paleoseismic study constrain the offset and timing of recent large earthquakes on the Xidatan–Dongdatan segment of the strike-slip Kunlun fault, northern Tibet. Displaced terrace risers and gullies preserved on the lowest and youngest terrace in the central part of the Xidatan–Dongdatan valley indicate that the offset produced by the most recent earthquake is 3–6 m, which is much smaller than what has been previously estimated; however, it is consistent with the slip of historical earthquakes along the Kunlun fault and recent well-recorded large earthquakes on other strike-slip faults. Accumulated offsets on higher terraces indicate repeated seismic activity of the Kunlun fault. We assume a 150 ± 20-km- long surface rupture for the most recent event based on roughly continuous linear features on remote-sensing images and distinct mole tracks in the field. The lack of seismicity records in the region earlier than 100 years ago led us to carry out paleoseismic investigation. Samples collected from the faulted upper layer show that the most recent large event on the Xidatan–Dongdatan segment is not older than 663 yr b.p. At least three prehistoric events are identified on the trench wall. Due to a lower constraint on the offset produced by the most recent earthquake, it would be necessary to reevaluate the seismic behavior of the Xidatan–Dongdatan segment.

Evidence of Quaternary activity along the Deshir Fault: implication for the Tertiary tectonics of Central Iran

Geological and geomorphologic offsets are used to constrain the total displacement and estimate the slip rate of the right-lateral Deshir Fault. Cumulative morphologic offsets have been found along the southern portion of the fault, on the Iranian Plateau. High-resolution SPOT5 images (pixel size 2.5 m) combined with SRTM DEM document right-lateral offsets of rills, terrace risers and successive alluvial fan systems. Cumulative offsets range from 25 to 900 m and increase with relative elevation, hence relative age, of offset markers. The smallest cumulative offsets are most probably of Holocene age (12 ± 2 ka) and suggest that the fault slips at an average slip rate close to 2 mm yr−1. Coeval normal faulting is associated to strike-slip motion at several places along the southern portion of the fault. Normal and probably active faults are encountered within the High Zagros 70 km ahead the tip of the Deshir Fault and may suggest the fault is propagating southwards. The total displacement of the Deshir fault, estimated from right-lateral offset of the Nain-Baft suture, is 65 ± 15 km. The total displacement would have accumulated over the last 25–40 Ma at an averaged Holocene slip rate of 2 mm yr−1. Placing these observations within the framework of the tectonics of Iran allows a discussion of the timing of the transition between collision and subduction in Eastern Iran.

Surface deformation related to kink-folding above an active fault: Evidence from geomorphic features and co-seismic slips

Abstract By means of a geomorphological study using 40 m digital elevation model, structural reconstruction by field data, and related geodetic results, we reevaluate the geomorphic features in the Hsinshe area, where multi-step terraces have been previously documented and supposedly provide more information of the neotectonic history. Our results show that two kink-shaped scarps can be discriminated from other terrace risers, which are probably formed by folding instead of faulting as suggested by previous researchers. Two E–W-reconstructed hanging wall cross sections in the north and south show that the fault plane of Chelungpu fault flattens to the east and sinks to the south, creating a monoclinal hanging wall resembling a quarter hemisphere in terms of a 3D model. We propose a kinetic model to explain the surface monocline fold: it is developed when the fault plane presents a fault-bend, such as the case along the Chelungpu fault at Hsinshe. The co-seismic deformation from the 1999 Chi-Chi earthquake demonstrates that the model is probably valid. Furthermore, the higher terrace showing larger deformation indicates the influences of active structures on terraces have continuously acted for a long time. The westward tilting of the hanging wall terraces result from the action of the Chelungpu fault and its related structural geometry. Based on the optical-stimulated-luminescence age of 55.0±12.6 ka of the highest terrace, we can compute the vertical rates across the main thrust and fold scarp in the hanging wall as 7.0 and 2.5 m/kyr, respectively.

Soil fertility management in the mid-hills of Nepal: Practices and perceptions

Sustaining soil fertility is essential to the prosperity of many households in the mid-hills of Nepal, but there are concerns that the breakdown of the traditional linkages between forest, livestock, and cropping systems is adversely affecting fertility. This study used triangulated data from surveys of households, discussion groups, and key informants in 16 wards in eastern and western Nepal to determine the existing practices for soil fertility management, the extent of such practices, and the perception of the direction of changes in soil fertility. The two principal practices for maintaining soil fertility were the application of farmyard manure (FYM) and of chemical fertilizer (mainly urea and diammonium phosphate). Green manuring, in-situ manuring, slicing terrace risers, and burning plant residues are rarely practiced. FYM usage was variable with more generally applied to khet land (average 6053 kg fresh weight manure ha−1) than to bari land (average 4185 kg fresh weight manure ha−1) with manure from goats and poultry preferred above that from cows and buffaloes. Almost all households (98%) apply urea to khet land and 87% to bari land, with 45% applying diammonium phosphate to both types of land. Application rates and timings of applications varied considerably both within and between wards suggesting poor knowledge transfer between the research and farming communities. The benefits of chemical fertilizers in terms of ease of application and transportation in comparison with FYM, were perceived to outweigh the widely reported detrimental hardening of soil associated with their continued usage. Among key informants, FYM applied in conjunction with chemical fertilizer was the most popular amendment, with FYM alone preferred more than chemical fertilizer alone – probably because of the latter’s long-term detrimental effects. Key informant and householder surveys differed in their perception of fertility changes in the last decade probably because of differences in age and site-specific knowledge. All key informants felt that fertility had declined but among households, only about 40% perceived a decline with the remainder about evenly divided between no change and an increase. Householders with small landholdings ( 2 ha) were more likely to perceive declining fertility. Perceived changes in soil fertility were not related to food self-sufficiency. The reasons for the slow spread of new technologies within wards and the poor understanding of optimal use of chemical fertilizers in conjunction with improved quality FYM may repay further investigation in terms of sustaining soil fertility in this region.

The Aksay segment of the northern Altyn Tagh fault: Tectonic geomorphology, landscape evolution, and Holocene slip rate

Millennial slip rates have been determined for the Altyn Tagh fault (ATF) at three sites near Aksay (∼94°E) in northeastern Tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10Be‐26Al surface exposure dating. Up to nine main surfaces are defined on the basis of morphology, elevation, and dating. The abandonment age of some surfaces is constrained by radiocarbon dating, which typically coincides with the youngest cosmogenic ages for a particular surface. Older surface exposure ages are taken to represent the duration of terrace emplacement. Cumulative offsets range from 20 to 260 m and fall in distinct groups, indicative of climatically modulated regional landscape formation. Most samples are younger than ∼14 ka and postdate the Last Glacial Maximum. The end of the early Holocene optimum marks the boundary between the ages of the two main terrace levels at 5–6 ka. At this longitude the ATF is divided into a northern and southern branch. The northern ATF should thus yield a minimum rate for the ATF system. Slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results, yielding an average Holocene rate of 17.8 ± 3.6 mm/yr. It is ∼9 mm/yr less than the long‐term rate obtained near Tura at ∼87°E (26.9 ± 6.9 mm/yr), in keeping with the inference of an eastward decreasing rate on the ATF, due to increased thrusting to the south. However, it remains twice the rate determined by GPS studies.

Topographic Shelter and Conifer Establishment and Mortality in an Alpine Environment, Glacier National Park, Montana

We examined the importance of periglacial shelter in the spatial distribution of conifers at and above alpine treeline. Using a detailed field-based method, we sampled a total of 211 conifer patches at three study locations in Glacier National Park (GNP), Montana. Conifers were found to be nonrandom spatial associates of three periglacial shelter types: boulders, terrace risers, and combination shelters. Our results indicate that conifer establishment and survival in this extreme mountain environment is connected to shelter availability and shelter type.

Borehole Radar Delineation of the Ventersdorp Contact Reef in Three Dimensions

A large portion of South Africa‘s gold reserve comes from the Ventersdorp Contact Reef (VCR). The VCR is a thin, tabular ore body, generally less than 1.2 m thick. The geometry of the VCR is mainly controlled by slopes, terraces, and faults. The gold is concentrated in palaeo-river channels situated on river terraces and not on the confining terrace risers or slopes, so there is a good correlation between topography and grade. The geophysical problem is to determine the reef geometry before mining begins, in order to plan optimal ore extraction.Borehole radar has already been shown to be a suitable technique for mapping topography on the VCR because of the favourable electrical property contrast between the footwall rocks and the overlying lavas. Here, a forward model is used to resolve the directional ambiguity inherent in low-frequency borehole radar data and to accurately position the target reflection in space. The data from five boreholes within a 200 m square block of ground are combined in a single model to estimate the topography of the ore body within the block. The illumination lines from the radar forward model are positioned in 3D. They are incorporated with other ore-body elevation data from mapping and drilling to improve the geological model of the ore body within the block.The spatial resolution of the geological model is substantially improved with borehole radar. Small faults and other changes in topography are accurately positioned, giving warning of oncoming changes in mining conditions. Terraces and slopes are mapped, facilitating planning of the optimal extraction of the gold within the block. In areas where exploration drilling is primarily undertaken to determine the structure of the ore body rather than its grade, borehole radar provides an effective alternative to conventional drilling.

Runoff and soil loss from bench terraces. 2. An event‐ based erosion process model

SummaryDespite widespread bench terracing of rainfed hillsides in upland West Java, soil loss rates remain high. This paper reports measurements of sediment yield from terrace risers and beds and from terrace units made during three consecutive rainy seasons. The results demonstrate that soil loss from the terraces occurs in two stages: rainfall‐driven transport by splash and shallow overland flow (wash) from the terrace riser and bed to a central drain is followed by a combination of onward wash transport of fine sediment and entrainment by runoff of coarser sediment deposited in the drain. A model (TEST: Terrace Erosion and Sediment Transport) was developed, describing these processes as a function of vegetation and soil surface cover and the presence of a layer of deposited sediment. The model was calibrated using some of the measured sediment yield data and subsequently tested by simulating the remaining data. The results were satisfactory and modelled fractions of sediment transported by splash, wash and flow‐driven runoff transport generally compared well with observed fractions of fine and coarse particles in eroded sediment from the various plots.

Location and geometry of the Wellington Fault (New Zealand) defined by detailed three‐dimensional georadar data

Earthquakes with surface‐wave magnitudes of 7.3–7.9 are estimated to be associated with the rupture of the Wellington Fault at relatively regular intervals of 500–770 years. The last such earthquake probably happened between AD 1510 and 1660. Along its southern segment, the Wellington Fault passes through Wellington, New Zealand's capital, and the densely populated Hutt Valley. It is considered to be a highly hazardous structure. To map the shallow geometry of the Wellington Fault, we have collected 3‐D ground‐penetrating radar (georadar) data at two sites along the fault in the Hutt Valley. At one site, the first ever georadar fault plane reflections from an active strike‐slip fault are observed. They coincide with conspicuous diffractions generated by abrupt truncations of structures against the fault plane. These georadar data provide the most vivid shallow images of any active fault surveyed to date. At the second site, apparent offsets of lineaments in the sedimentary sections on either side of the fault are consistent with ∼20 m of dextral displacement estimated from the offset of a nearby terrace riser. The dips and minimum depth extents of the primary zones of fault displacement at the two sites are 55–75°SE and ∼20 m and 72–84°SE and ∼12 m, respectively. Although the georadar‐defined zones of faulting are a few meters wide, prominent reflection fabrics suggest that shearing, fracturing, and crushing extend for several tens of meters on either side of the fault.

Regeneration of Monodominant Stands of Banj Oak (Quercus leucotrichophora A. Camus) on Abandoned Terraces in the Central Himalayas

Banj oak (Quercus leucotrichophora A. Camus) is an important hardwood species of the Central Himalayas that is heavily used for fuelwood, fodder and as an agricultural mulch. Disturbed sites that create large canopy openings and exposed topsoil are widely reported to promote stands of chir pine (Pinus roxburghii Sarg.). However, under some circumstances, observations contradictory to these findings suggest that stands of banj oak can also originate after agricultural abandonment in this region. To investigate this, a chronosequence of agricultural terraces, that had been subjected to differing levels of post-abandonment disturbance (grazing, fuelwood, fodder and litter collection), were sampled to record changes in regeneration size and density of chir pine and banj oak. Regeneration and soils on the flat parts of the terraces were compared to that on the risers of the terraces. Banj oak density was found to be higher than chir pine on terraces under both high and low post-abandonment disturbance for the chronosequence. Banj oak was also found to predominate on the terrace risers. Oak diameter was negatively affected by increased disturbance, but height was not affected. Chir pine was found to grow equally well in terms of height, diameter and stem density on all parts of the terrace, with a preference for sites with high post-abandonment disturbance. The length of time since field abandonment had no effect on stem density for either species. No significant differences were detected in nitrogen and soil carbon status between the flats and the risers of the terraces. Soil moisture content was found to be higher on the risers of the terraces, with soils on the risers higher in clay content. Results from this study show that management practices used on fields while they are still under cultivation are the main agent responsible for the release of large numbers of banj oak seedlings and sprouts on the risers of the terraced fields. Terraced lands thus act as a nursery for the subsequent release and development of future stands dominated by banj oak. Widespread abandonment of property in the late 18th century due to war and epidemics may therefore have led to the formation of many of the old banj stands existing today.

Terrace erosion and sediment transport model: a new tool for soil conservation planning in bench-terraced steeplands

Despite widespread bench-terracing soil erosion remains a major problem in Java’s uplands. To elucidate the causes for this lack of impact, runoff and erosion processes were studied at a variety of spatial scales within a volcanic catchment in West Java. Research indicated that soil loss occurs via rain splash and wash of rainfall-detached sediment by shallow overland flow from the terrace riser and bed, and via runoff entrainment of sediment deposited in the central terrace toe drain. The terrace erosion and sediment transport mode (TEST) was developed to physically describe these processes, as a function of vegetation and soil surface cover where appropriate, yet use as few parameters as possible. Runoff generation was described by the spatially variable infiltration model (SVIM) and a two parameter rainfall depth-intensity distribution was assumed to derive a simple analytical expression for storm runoff depth. In a similar manner expressions were derived for effective rainfall kinetic energy to predict rainfall-driven transport using a newly developed model, and for effective runoff rate to predict flow-driven transport using GUEST model theory. The model and its components were tested using measured runoff and soil loss from 31 sections of terrace beds or risers and from six terrace units during two seasons. The model generally performed satisfactorily and provides a useful new tool for assessing the impacts of soil conservation measures on bench terrace runoff and soil loss.

Late Holocene Liquefaction Features in the Dominican Republic: A Powerful Tool for Earthquake Hazard Assessment in the Northeastern Caribbean

Several generations of sand blows and sand dikes, indicative of significant and recurrent liquefaction, are preserved in the late Holocene alluvial deposits of the Cibao Valley in northern Dominican Republic. The Cibao Valley is structurally controlled by the Septentrional fault, an onshore section of the North American-Caribbean strike-slip plate boundary. The Septentrional fault was previously studied in the central part of the valley, where it sinistrally offsets Holocene terrace risers and soil horizons. In the eastern and western parts of the valley, the Septentrional fault is buried by Holocene alluvial deposits, making direct study of the structure difficult. Liquefaction features that formed in these Holocene deposits as a result of strong ground shaking provide a record of earthquakes in these areas. Liquefaction features in the eastern Cibao Valley indicate that at least one historic earthquake, probably the moment magnitude, M 8, 4 August 1946 event, and two to four prehistoric earthquakes of M 7 to 8 struck this area during the past 1100 yr. The prehistoric earthquakes appear to cluster in time and could have resulted from rupture of the central and eastern sections of the Septentrional fault circa A.D. 1200. Liquefaction features in the western Cibao Valley indicate that one historic earthquake, probably the M 8, 7 May 1842 event, and two prehistoric earthquakes of M 7-8 struck this area during the past 1600 yr. Our findings suggest that rupture of the Septentrional fault circa A.D. 1200 may have extended beyond the central Cibao Valley and generated an earthquake of M 8. Additional information regarding the age and size distribution of liquefaction features is needed to reconstruct the prehistoric earthquake history of Hispaniola and to define the long-term behavior and earthquake potential of faults associated with the North American-Caribbean plate boundary. Manuscript received 6 September 2002.

Measurements of rain splash on bench terraces in a humid tropical steepland environment

AbstractSoil loss continues to threaten Java's predominantly bench‐terraced volcanic uplands. Sediment transport processes on back‐sloping terraces with well‐aggregated clay‐rich oxisols in West Java were studied using two different techniques. Splash on bare, cropped, or mulched sub‐horizontal (2–3°) terrace beds was studied using splash cups of different sizes, whereas transport of sediment on the predominantly bare and steep (30–40/deg ) terrace risers was measured using a novel device combining a Gerlach‐type trough with a splash box to enable the separate measurement of transport by wash and splash processes. Measurements were made during two consecutive rainy seasons. The results were interpreted using a recently developed splash distribution theory and related to effective rainfall erosive energy. Splash transportability (i.e. transport per unit contour length and unit erosive energy) on the terrace risers was more than an order of magnitude greater than on bare terrace beds (0·39–0·57 versus 0·013–0·016 g m J−1). This was caused primarily by a greater average splash distance on the short, steep risers (&gt;11 cm versus c. 1 cm on the beds). Splashed amounts were reduced by the gradual formation of a protective ‘pavement’ of coarser aggregates, in particular on the terrace beds. Soil aggregate size exhibited an inverse relationship with detachability (i.e. detachment per unit area and unit erosive energy) and average splash length, and therefore also with transportability, as did the degree of canopy and mulch cover. On the terrace risers, splash‐creep and gravitational processes transported an additional 6–50% of measured rain splash, whereas transport by wash played a marginal role. Copyright © 2002 John Wiley &amp; Sons, Ltd.