Large Elevation Differences Research Articles

Impact of tropospheric modelling on GNSS vertical precision: an empirical analysis based on a local active network

ABSTRACTThe troposphere affects Global Navigation Satellite System (GNSS) signals due to the variability of the refractive index. Tropospheric delay is a function of the satellite elevation angle and the altitude of the GNSS receiver and depends on the atmospheric parameters. If the residual tropospheric delay is not modelled carefully a bias error will occur in the vertical component. In order to analyse the precise altimetric positioning based on a local active network, four scenarios in Southern Spain with different topographical, environmental, and meteorological conditions are presented, considering both favourable and non-favourable conditions. The use of surface meteorological observations allows us to take into account the tropospheric conditions instead of a standard atmosphere, but introduces a residual tropospheric bias which reduces the accuracy of precise GNSS positioning. Thus, with short observation times it is recommended not to estimate troposphere parameters, but to use an a priori model together with the standard atmosphere. The results confirm that it is possible to achieve centimetre-scale vertical accuracy and precision with real time kinematic positioning even with large elevation differences with respect to the nearest reference stations. These numerical results may be taken into consideration for improving the altimetric configuration of the local active network.

Quantifying the Effects of Normalisation of Airborne LiDAR Intensity on Coniferous Forest Leaf Area Index Estimations

The range between a sensor and the target, the incidence angle, and the target reflectance, are known factors that can influence the intensity values of LiDAR data and consequently, its use in many applications. However, very few studies have provided a quantitative analysis of the effects of normalisation of these three factors on forest leaf area index (LAI) estimations. In this paper, using two coniferous tree species (i.e., Scotch pine and Larch pine) as a case study, the effects of intensity normalisation on coniferous forest LAI estimations have, for the first time, been systematically examined and quantified. It was found that the intensity normalisation had a generally positive effect on the improvement of coniferous forest LAI estimations. However, the improvements were very minor. Specifically, the range normalisation did not improve the accuracy of the LAI estimation for either of the two coniferous tree species. The incidence angle and reflectance normalisation improved the accuracy of the LAI estimation for Scotch pine forests; however, they had no effect on the improvement of the LAI estimation for Larch pine forests. This experimental study suggests that range normalisation is not required for forest LAI estimations in areas with small elevation differences (i.e., less than 114 m). The incidence angle and target reflectance normalisation can marginally improve the accuracy of coniferous forest LAI estimations. However, the extent of this improvement varies among species, depending on the choice of incidence angle and reflectance coefficient. Overall, the effects of normalisation of airborne LiDAR intensity on coniferous forest LAI estimations are closely related to topographic conditions (i.e., elevation and slope), the tree species composition, and its associated structural attributes. Therefore, further research should explore the effects of LiDAR intensity normalisation on forest LAI estimations in regions with large elevation differences and diverse forest structures.

Variability of the water availability in a river lake system – A case study of Lake Symsar

AbstractIt is predicted that climate change will result in the diminution of water resources available both on global and regional scales. Local climate change is harder to observe and therefore, while counteracting its effects, it seems advisable to undertake studies on pertinent regional and local conditions. In this research, our aim was to assess the impact of a river and its catchment on fluctuations in the water availability in a natural lake which belongs to a post-glacial river and lake system. River and lake systems behave most often like a single interacting hydrological unit, and the intensity of water exchange in these systems is quite high, which may cause temporary water losses. This study showed that water in the analyzed river and lake system was exchanged approx. every 66 days, which resulted from the total (horizontal and vertical) water exchange. Also, the management of a catchment area seems to play a crucial role in the local water availability, as demonstrated by this research, where water retention was favoured by wooded and marshy areas. More intensive water retention was observed in a catchment dominated by forests, pastures and wetlands. Wasteland and large differences in the land elevation in the tested catchment are unfavourable to water retention because they intensify soil evaporation and accelerate the water run-off outside of the catchment. Among the actions which should be undertaken in order to counteract water deficiencies in catchment areas, rational use and management of the land resources in the catchment are most often mentioned.

Analysis of variability and trends in rainfall over northern Ethiopia

Rainfall is a key component of the hydrological cycle, and its spatiotemporal variability is essential from the both scientific and practical perspectives. This study is focused on analysis of temporal variability and trends in historical rainfall records for stations in the Geba River basin. The Geba catchment is surrounded by the Danakil basin in the east, by the Tekeze River basin in the south, and the Werie River basin in the west which is located in the northern Ethiopia regional state of Tigray between 38° 38′ E and 39° 48′ E and 13° 18′ N and 14° 15′ N. The climate over the basin is semi-arid and has large elevation differences varying from 926 to 3301 m above mean sea level. Daily rainfall data of 43 years measured at seven stations in the basin for the period of 1971 to 2013 for annual and seasonal rainfall trends have been processed and used for the analysis. The non-parametric Mann–Kendall test and the Sen’s slope estimator have been used to identify the existence of trends and slope magnitude in rainfall. Results revealed that although there was a mix of positive and negative trends, they were no statistically significant except at one station which showed an increasing trend in annual rainfall. Considering rainfall in different seasons, an increase in rainfall was observed in two stations in the wet season which, however, was not statistically significant. For the remaining stations, a weak decline in wet season rainfall (not statistically significant at 95 % confidence level) for four stations and absence of trend for one station were noticed. Furthermore, no statistically significant trend (positive or negative) was evident for the dry season rainfall. Results of this study may prove useful in the preparation of climate change mitigation and adaptation strategies in rainfed agricultural and water supply systems in the region.

Evaluating landslide hazards using RCP 4.5 and 8.5 scenarios

Recently, extreme meteorological events have occurred frequently owing to climate change and its influence. Impacts of concentrated precipitation events include the damage caused by landslides. Many areas in Gangwondo (Korea) are located at high elevation and have large elevation differences; these areas are thus at high risk of landslides. The purpose of this study was to evaluate the landslide hazard of the province using representative concentration pathways (RCP) scenarios 4.5 and 8.5 and to compare results. This study produced an optimal landslide model for the province through analysis of variables and points of landslide origin. Estimates indicate that the landslide hazard area will increase to 154 km2. The RCP 8.5 scenario showed a larger (by about 59 km2) landslide hazard area than the RCP 4.5 scenario. The uncertainty of climate change scenarios was also explored using statistical values of each scenario period. An overlay analysis (overlay of landslide hazard areas and land cover map) showed that 40.6 % of farmlands would be susceptible to landslides in 2070–2099 (RCP 8.5). Additionally, damage to the alpine agriculture due to landslides was also identified as a critical area. In the RCP 8.5 scenario, the land-use types that occupy more than 20 % of the landslide hazard area are transportation, recreational facilities, and vinyl house for farming. This suggests that casualties from landslides will increase in future. It also highlights a lack of policies to manage development. Therefore, the local government of Gangwondo should consider landslide hazard areas when planning future land uses.

Duration and seasonality of hourly extreme rainfall in the central eastern China

Compared with daily rainfall amount, hourly rainfall rate represents rainfall intensity and the rainfall process more accurately, and thus is more suitable for studies of extreme rainfall events. The distribution functions of annual maximum hourly rainfall amount at 321 stations in China are quantified by the Generalized Extreme Value (GEV) distribution, and the threshold values of hourly rainfall intensity for 5-yr return period are estimated. The spatial distributions of the threshold exhibit significant regional differences, with low values in northwestern China and high values in northern China, the mid and lower reaches of the Yangtze River valley, the coastal areas of southern China, and the Sichuan basin. The duration and seasonality of the extreme precipitation with 5-yr return periods are further analyzed. The average duration of extreme precipitation events exceeds 12 h in the coastal regions, Yangtze River valley, and eastern slope of the Tibetan Plateau. The duration in northern China is relatively short. The extreme precipitation events develop more rapidly in mountain regions with large elevation differences than those in the plain areas. There are records of extreme precipitation in as early as April in southern China while extreme rainfall in northern China will not occur until late June. At most stations in China, the latest extreme precipitation happens in August-September. The extreme rainfall later than October can be found only at a small portion of stations in the coastal regions, the southern end of the Asian continent, and the southern part of southwestern China.

Is Adaptation to Perceived Interocular Differences in Height Explained by Vertical Fusional Eye Movements?

To find out whether adaptation to a vertical prism involves more than fusional vertical eye movements. Adaptation to a vertical base-up 3 prism diopter prism was measured in a custom-programmed Maddox test in nine visually normal emmetropic subjects (mean age 27.0 ± 2.8 years). Vertical eye movements were binocularly measured in six of the subjects with a custom-programmed binocular video eye tracker. In the Maddox test, some subjects adjusted the perceived height as expected from the power of the prism while others appeared to ignore the prism. After 15 minutes of adaptation, the interocular difference in perceived height was reduced by on average 51% (from 0.86°-0.44°). The larger the initially perceived difference in height in a subject, the larger the amplitude of adaptation was. Eye tracking showed that the prism generated divergent vertical eye movements of 1.2° on average, which was less than expected from its power. Differences in eye elevation were maintained as long as the prism was in place. Small angles of lateral head tilt generated large interocular differences in eye elevation, much larger than the effects introduced by the prism. Vertical differences in retinal image height were compensated by vertical fusional eye movements but some subjects responded poorly to a vertical prism in both experiments; fusional eye movements were generally too small to realign both foveae with the fixation target; and the prism adaptation in the Maddox test was fully explained by the changes in vertical eye position, suggesting that no further adaptational mechanism may be involved.

Interpreting cultural remains in airborne laser scanning generated digital terrain models: effects of size and shape on detection success rates

In this study, detection success rates were evaluated for cultural remains that were detected manually based on interpretation of digital terrain models (DTM) derived from airborne laser scanning data and with a resolution of 1, 5 and 10 points m−2. The group of cultural remains included charcoal kilns, charcoal pits, hollow-roads, various pits, house foundations, tar kilns, grave mounds and pit-falls. The effects on the interpretation success of different types of cultural remains and their physical properties were studied: size, shape and elevation difference showing that the detection success rates varied considerably. The main tendency was that large cultural remains with clear geometrical shape (ovals and circles) and large elevation difference were much more successfully detected and classified compared to the smaller ones, especially those without a clear geometrical shape. The study also showed that it was the identification of the larger structures which profited most from an increased resolution of the DTM, and it was of no help to increase resolution in order to improve the identification of the irregularly shaped cultural remains.

Upward recharge through groundwater depression cone in piedmont plain of North China Plain

summary Whether a recharge was induced by groundwater depression cones is a crucial issue for water resource management. In the North China Plain, shallow groundwater had been over-pumped since 1970s and many groundwater depression cones formed. The groundwater depression cone, Daceying–Machang, occurred even in the piedmont plain. In the area, water levels of deep and shallow groundwater were observed since 2005 and field survey was conducted in the dry season 2010. The upward recharge induced by the depression cone is verified based on water level records, major ions, 2 H, 18 O and kinds of statistical analyses. Since August 2006, the water level of the deep groundwater ascended by 1.9 mm/d. High correlations (r = 0.86, s = 0.67) between the water level series of shallow and deep groundwater were found by two distinct correlation analyses only in the center of depression cone. Further, the reversion of hydraulic gradient of the depression cone occurred in dry seasons since September 2008. Hydro-geochemical features of the shallow groundwater are consistent with deep groundwater in the center of depression cone, which was demonstrated by the fuzzy C-means clustering based on principal components and paired t test, respectively. It is concluded that the deep groundwater recharged the shallow groundwater from the center of the depression cone. As a result, the groundwater mixture occurred that improves the quality of the shallow groundwater. Seasonally changed flow of shallow groundwater enhanced the mixture. The persistent overpumping of shallow groundwater and the large elevation difference (around 1200 m) between the recharge zone and the discharge point of deep groundwater facilitate the upward recharge.

ANALYSIS OF SOUTH WEST MONSOON RAINFALL TREND USING STATISTICAL TECHNIQUES OVER NETHRAVATHI BASIN

The analysis of rainfall for agricultural purposes must include information concerning the trends or changes of precipitation, the start end and length of the rainy season, the distribution of rainfall amounts through the year and the risk of dry and wet spells. The present study is mainly concerned with the changing trend of rainfall over Nethravathi river basin, located in coastal region of Karnataka state. Nethravathi river originates in the peaks of western ghats and flows towards westwards. The climate over the basin is humid and has large elevation difference varying from 0 to 1400 m above msl. Precipitation trend analysis based on elevation, rain gauge stations were grouped into two regions with similar precipitation characteristics to perform a regional analysis. Daily rainfall data of 40 years from 1971 to 2010 has been processed in the study to find out the monthly variability of south west monsoon (June, July, August, and September) season. Mann-Kendall (MK) test and Sens’s slope estimator has been used to determine trend and slope magnitude. Long-term analysis (1971 to 2010) was carried out for both regions and results have been compared. Monthly precipitation trend has been identified here to accomplish the objective which shows 40 years of data. From the analysis, it is found that there are decreasing trend of precipitation in some months and increasing trend in some other months. The statistical tests which are used in the study are indicative of overall changes in precipitation trend during the south west monsoon.

Global patterns of mobile carbon stores in trees at the high‐elevation tree line

ABSTRACTAim Across all latitudes, high‐elevation tree lines represent a drastic change in the dominant plant life‐form, from upright trees to low‐stature alpine plants. Although associated with low temperatures, the physiological mechanisms controlling this boundary are still not clear. The growth‐limitation hypothesis assumes a direct low‐temperature restriction of tissue formation at otherwise sufficient photoassimilation. In order to test this hypothesis, we present a global synthesis of previously published and new data on tree carbon supply status at high‐elevation tree lines.Location Global; 13 regions between 68° N and 45° S.Methods Late‐season concentrations of non‐structural carbohydrates (NSC) in foliage and branch wood were measured at three elevations across the tree line ecotones, from upper tall forests (timber line) to the edges of aborescent tree growth (tree line). Year‐round records of −10 cm soil temperatures were taken at the tree line.Results Despite large differences in elevation and season length, the mean growing season temperature at the tree line was similar (approximately 6.6 °C) between all sites. NSC concentrations were not depleted at any of the elevation gradients between timber line and tree line, indicating no shortage of C at the uppermost tree stands. Tested across all sites, NSC concentrations in fact significantly increased with elevation. On average, NSC increased by 18% in leaves and 26% in branch wood from the lowest to the highest stands, primarily due to higher starch concentrations rather than free sugars. Hence, these responses do not reflect osmotic adjustments to lower temperatures at the end of the growing season.Main conclusions This global data set contributes to a mechanistic understanding of tree line formation based on biological principles across climatic zones and tree genera. No evidence of C shortage was found at the high‐elevation tree line in either seasonal and non‐seasonal regions. The increasing trend of NSC concentrations with elevation is in line with the growth‐limitation hypothesis.

The evolution of the Danube gateway between Central and Eastern Paratethys (SE Europe): Insight from numerical modelling of the causes and effects of connectivity between basins and its expression in the sedimentary record

The Pannonian and Dacic Basins in SE Europe are presently connected by the Danube River across the South Carpathians, to which they are in a back-arc and foreland position respectively. Part of the Paratethys realm during the Neogene, open water communication between the basins was interrupted by the Late Miocene uplift of the Carpathians. Different mechanisms have been proposed for the formation of the Danube gateway: capture of the upstream lake or an upstream river or incision of an antecedent river. Estimates on its age range from Late Miocene to Quaternary. A related issue is the effect of the large Mediterranean sea level fall related to the Messinian Salinity Crisis on the Paratethys subbasins, specifically the “isolated” Pannonian Basin. In a synthetic numerical modelling study, using a pseudo-3D code integrating tectonics, surface processes and isostasy, we addressed the causes and effects of changes in connectivity between two large sedimentary basins separated by an elevated barrier. Specifically, we aimed to find the expression of connectivity events in the sedimentary record in general and the consequences for the evolution of the Pannonian–Dacic area in particular. We studied a range of parameters including the geometry and uplift rate of the barrier, downstream sea level change and lithosphere rigidity. We found that changes in connectivity are expressed in the sedimentary record through their effect on base level in the upstream basin and supply in the downstream basin. The most important factors controlling the response are the elevation difference between the basins and the upstream accommodation space at the time of reconnection. The most pronounced effect of reconnection through lake capture is predicted for a large elevation difference and limited upstream accommodation space. Downstream increase in sediment supply is dependent on the latter rather than the reconnection event itself. Of the parameters we tested, the rigidity of the lithosphere was found to be of major importance by its control on sediment loaded subsidence and generation of accommodation space. A downstream sea level change is unlikely to induce capture, but may affect the upstream lake level by enhancing incision in a pre-existing gateway. In the Pannonian–Dacic region, the mechanically weak, continuously subsiding Pannonian lithosphere allowed accommodation of significant volumes of continental sedimentation and as a consequence, transfer of excess sediment to the downstream Dacic Basin was only gradual. The Messinian sea level fall in the Dacic Basin could have been recorded in the Pannonian Basin only if a connection between the basins already existed. More detailed modelling of river incision taking into account lateral differences in erodibility in the South Carpathians will be required to give better time constraints on the formation of the Danube Gateway.

Intensity-dependent parameterization of elevation effects in precipitation analysis

Abstract. Elevation effects in long-term (monthly to inter-annual) precipitation data have been widely studied and are taken into account in the regionalization of point-like precipitation amounts by using methods like external drift kriging and cokriging. On the daily or hourly time scale, precipitation-elevation gradients are more variable, and difficult to parameterize. For example, application of the annual relative precipitation-elevation gradient to each 12-h sub-period reproduces the annual total, but at the cost of a large root-mean-square error. If the precipitation-elevation gradient is parameterized as a function of precipitation rate, the error can be substantially reduced. It is shown that the form of the parameterization suggested by the observations conforms to what one would expect based on the physics of the orographic precipitation process (the seeder-feeder mechanism). At low precipitation rates, orographic precipitation is "conversion-limited", thus increasing roughly linearly with precipitation rate. At higher rates, orographic precipitation becomes "condensation-limited" thus leading to an additive rather than multiplicative orographic precipitation enhancement. Also it is found that for large elevation differences it becomes increasingly important to take into account those events where the mountain station receives precipitation but the valley station remains dry.

ネパール東部・サガルマータ県における居住と地形条件との関係―地形図のデジタル化とＧＩＳによる解析―

Nepal is a mountainous country located between India and China, and has a large elevation difference in a north-south direction. The elevation difference accounts for physical and social diversities in the country. This study examines the relationship between topographic factors and distribution of residential areas in the Sagarmatha zone of eastern Nepal using information derived from topographical maps including a high-resolution digital elevation model (DEM). Residential areas in the study area are distributed from 400 to 5,200 m in altitude. More than 80% of them are concentrated from 1,000 to 2,500 m, and 2% are located above 3,000 m. Residential areas below 3,500 m tend to occur on relatively steep ridges, and those below 2,500 m tend to occur on north-facing slopes. Residential areas above 3,500 m tend to occur on relatively gentle valley sides and south-facing slopes. These differences in the residential environment by elevation are attributed to differences in topographic and climatic condition. This study suggests that GIS technology and digital data can provide basic information at a macro scale to solve regional problems in Nepal.

Recent glaciation at high elevations on Arsia Mons, Mars: Implications for the formation and evolution of large tropical mountain glaciers

The ∼166,000 km2fan‐shaped deposit at Arsia Mons contains three characteristic facies (ridged, knobby, and smooth), which are interpreted as the depositional remains of a cold‐based glacier that was present on the west–northwestern flanks in the Late Amazonian period of Mars history. Here, we consider several high‐elevation graben on the western flank of Arsia Mons that are interpreted as the source regions for late‐stage, cold‐based glaciers that overflowed graben walls, advanced tens to hundreds of kilometers downslope, experienced subsequent retreat, and left distinctive depositional features similar to those associated with cold‐based glaciers in the Dry Valleys of Antarctica. These new observations provide additional support for a cold‐based glacial interpretation of the Tharsis Montes fan‐shaped deposits. Morphological evidence suggests that the largest of these graben was the primary source region for the most proximal smooth facies lobes at Arsia Mons, and map‐plane ice sheet reconstructions are consistent with these observations. This relationship has significant implications for the relative ages of the individual facies within the fan‐shaped deposit, including the possibility that the smooth facies represents several distinct phases of glaciation. The high relief and large elevation differences between the upslope and downslope walls of these graben appear to be critical factors for ice accumulation and the generation/collection of rockfall within glacial accumulation zones. We suggest that rockfall was the dominant process responsible for debris‐cover formation on the glaciers sourced within these graben and consider the implications for the entire Arsia fan‐shaped deposit. New crater count data suggest that the fill material in the large Arsia graben formed within the past ∼100 Myr (model age of ∼65 Ma). Taken together, these new observations provide additional evidence for several periods of Late Amazonian climate change on Mars within the past few 100 Myr resulting in episodes of tropical mountain glaciation. Finally, MOLA topography reveals that several lobate features interpreted as remnant debris‐covered ice from the most recent phase of glaciation are presently hundreds of meters thick, suggesting the possibility of long‐term, near‐surface water ice survival in the equatorial regions of Mars.

A method for improving landscape scale temperature predictions and the implications for vegetation modelling

Understanding how environmental factors influence the spatial distribution of vegetation allows environmental managers to plan for issues such as climate change, ecological restoration and intensified land use. Elevation is often used as an indirect predictor of temperature, but this limits the applicability of environmental models to other study areas and introduces errors in mountainous terrain where variations in slope, aspect, and radiation can significantly alter the relationship between elevation and temperature. Some studies have developed estimates for temperature that also consider factors such as radiation, but these usually estimate the temperature for each location without considering the surrounding environment. In this study, average summer maximum and minimum temperatures were recorded at various locations on the Illawarra Escarpment, near Sydney, Australia. It was hypothesised that wind and air movements would average out large differences in elevation and radiation in mountainous terrain and cause the temperatures to be more strongly correlated with local averages of elevation and radiation than they are with the actual elevation and radiation where the temperatures were recorded. The use of local averages improved the estimate of average summer maximum temperature from a regression r 2 of 0.185 using elevation alone, to an r 2 of 0.685 when using canopy cover, local average elevation and local average radiation. In contrast, average summer minimum temperatures were better predicted using the elevation of each location without averaging. The results were applied to vegetation modelling by comparing a generalised additive model using the predicted average temperatures with a model using elevation. The overall classification accuracy for vegetation communities in the study area was improved from 46.4% to 61.8%. Therefore, improved temperature estimates also improved the explanatory performance of vegetation models.

Applying fuzzy theory and genetic algorithm to interpolate precipitation

A watershed management program is usually based on the results of watershed modeling. Accurate modeling results are decided by the appropriate parameters and input data. Rainfall is the most important input for watershed modeling. Precipitation characteristics, such as rainfall intensity and duration, usually exhibit significant spatial variation, even within small watersheds. Therefore, properly describing the spatial variation of rainfall is essential for predicting the water movement in a watershed. Varied circumstances require a variety of suitable methods for interpolating and estimating precipitation. In this study, a modified method, combining the inverse distance method and fuzzy theory, was applied to precipitation interpolation. Meanwhile, genetic algorithm (GA) was used to determine the parameters of fuzzy membership functions, which represent the relationship between the location without rainfall records and its surrounding rainfall gauges. The objective in the optimization process is to minimize the estimated error of precipitation. The results show that the estimated error is usually reduced by this method. Particularly, when there are large and irregular elevation differences between the interpolated area and its vicinal rainfall gauging stations, it is important to consider the effect of elevation differences, in addition to the effect of horizontal distances. Reliable modeling results can substantially lower the cost for the watershed management strategy.

ICESat measurement of Greenland ice sheet surface slope and roughness

AbstractThe Ice, Cloud and land Elevation Satellite (ICESat) in its 8 day repeat orbit mode provided data not only on the along-track surface slope, but also on the cross-track surface slope from adjacent repeat ground tracks. During the first 36 days of operation, four to five such repeat orbits occurred within 1 km in the cross-track direction. This provided an opportunity to use ICESat data to measure surface slope in the cross-track direction at 1 km scale. An algorithm was developed to calculate the cross-track surface slope. Combining the slopes in the cross-track and along-track directions gives a three-dimensional surface slope at 1 km scale. The along-track surface slope and surface roughness at 10km scale are also calculated. A comparison between ICESat surface elevation and a European Remote-sensing Satellite (ERS-1) 5 km digital elevation model shows a difference of 1–2 m in central Greenland where the surface slope is small, and >20m at the edge of Greenland where the surface slope is large. The large elevation difference at the edge is most likely due to the slope-induced error in radar altimeter measurement. Accurate surface slope data from ICESat will help to correct the slope-induced error of radar altimeter missions such as Geosat, ERS-1 and ERS-2.

The influence of lithology on hillslope development in the area of the Jacupiranga Alkaline Complex and its surroundings (São Paulo, Brazil)

The area of the Jacupiranga Alkaline Complex and its surroundings is characterized by a variety of slope forms. Their spatial differentiation and the differences in relative relief and hilltop heights are a function of lithology. Significant contrasts exist, particularly between the ultramafic rocks of the Alkaline Complex and the quartz-rich rocks of the surrounding Precambrian basement. Although climatic conditions are uniform, the physical and chemical properties of the weathering products formed on the various rock types are very different. Through their properties, they affect the hillslope processes and thereby influence the hillslope development. Slope-forming processes on deeply weathered ultramafic rocks are slow mass movements and chemical denudation. On the more resistant ultramafic rocks, wash processes appear to be more important. Wash and rapid mass movements predominate on gneisses, granites and mica schists. The geomorphological development of the Jacupiranga Alkaline Complex can be explained in terms of a long, continuous downwearing. The large differences in elevation within the Alkaline Complex suggest that the development towards a more differentiated relief may extend well back into the Tertiary. The mutual adjustment of slope forms, processes and lithological controls favoured the development of rock-dependent summit heights, where heights are determined by the steepness of the slopes and the spacing of the drainage lines. Climatic fluctuations in the Pleistocene failed to produce any fundamental change in the long-term development of the hillslopes as their duration was too short with respect to the relaxation time of the hillslopes or their influence was not great enough to alter the overall trend of slope development.

Second-order moment tensors of microearthquakes at The Geysers geothermal field, California

AbstractThe Geysers geothermal field is the site of intense microseismicity which appears to be associated with steam production. It seems that focal mechanisms of earthquakes at The Geysers vary systematically with depth, but P-wave first-motion focal mechanism studies have been hampered by inadequate resolution. In this study an unconstrained frequency domain moment tensor inversion method is used to over come P-wave first-motion focal sphere distribution problems and to investigate microearthquake source properties. A goal was to investigate the feasibility of using waveforms to invert for the second-order moment tensor of microearthquakes in the complex setting of The Geysers. Derived frequency-domain moment tensors for two earthquakes were verified by mechanisms estimated from P-wave first motions and required far fewer stations. For one event, 19 P-wave first motions were insufficient to distinguish between normal-slip and strike-slip focal mechanisms, but a well-constrained strike-slip solution was obtained from the waveform principal moment inversion using data from six stations. Improved waveform focal mechanism resolution was a direct consequence of using P- and S-wave data together in a progressive velocity-hypocenter inversion to minimize Green function errors. The effects of hypocenter mislocation and velocity model Green function errors on moment tensor estimates were investigated. Synthetic tests indicate that these errors can introduce spurious isotropic and compensated linear vector dipole components as large as 26 per cent for these events, whereas principal moment orientations errors were <8°. In spite of unfavorable recording geometries and large (0.6 km) station elevation differences, the results indicate that waveform moment tensor estimates for microearthquake sources can be robust and constrain source mechanisms using data from a relatively small number of stations.