ALBERT

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: The author has identified the following significant results. Nine photography interpretation tests were performed with a total of 19 different interpreters. Three tests were conducted with black and white intermediate scale photography and six tests with color infrared intermediate scale photography. The black and white test results show that the interpretation of vegetation mapped at the association level of classification is reliable for all the classes used at 61%. The color infrared tests indicate that the association level of mapping is unsatisfactory for vegetation interpretation of classes 1 and 6. Students' t-test indicated that intermediate scale black and white photography is significantly better than this particular color infrared photography for the interpretation of southeastern Arizona vegetation mapped at the association level.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: The effects of urbanization and highway construction on run-off, erosion and siltation on the Anacostia watershed was analyzed. The analysis was based on changes in land use patterns demonstrated by aerial photographs, geologic and hydrologic data. Subwatersheds were studied in terms of three hypothetical storms of different magnitudes. An approximately 10 percent increase in impervious surface can cause a 12 percent increase in peak discharge for storms of the magnitude of tropical storm Agnes, a 20 percent increase for a 10 hour storm and a 150 percent increase for a thunderstorm. The early discharge from a storm of Agnes' magnitude can be increased by 100 percent. Corresponding effects were observed in soil erosion and siltation from bare construction sites. These effects are interrelated with sewage, oil, and chemical pollution and inadequate public transportation. The net result is steady degradation of the local environment, the estuary and the bay.

Beschreibung: No abstract available

Beschreibung: The author has identified the following significant results. A new procedure to determine snowcovered areas has been devised. Aside from problems in heavily forested areas this method shows promise in predicting snowmelt runoff from mountain areas and will also assist in energy balance modeling of large snowfields. Snowcover results compare favorably with measurements made by high altitude aircraft photography. Changes in snowcover in areas as small as 3 x 5 km can be determined from ERTS-1 images by both optical and electronic methods. Snowcover changes determined by these two methods in the experimental South Cascade Glacier Basin were verified by field mapping. Image enahancement techniques on ERTS-1 images of large Alaskan glaciers (the Hubbard, Yentna, and Kahiltna) have given new insights into the large-scale structures and flow dynamics of these potentially hazardous glaciers. The Hubbard Glacier, in particular, is one which poses a threat to man and should be monitored for future changes.

Beschreibung: The author has identified the following significant results. ERTS-1 imagery clearly identifies the relationships between the status of erosion, effluent patterns affected by the coastal current, and the cultural construction activities. Simple photographic techniques can be used for detecting water mass distribution separately from cloud cover and also noise caused by reflected sunlight from wave surfaces. Polluted water does not diffuse continuously into the oceanic water, but forms masses in the water in the Kuroshio area. The polluted or turbid water in the area just north of the Tomogashima Channel, the south outlet of the Osaka Bay, shows that the northward tidal current runs in a clockwise eddy at the tidal period when the imagery was taken. Such an eddy-like pattern of tidal current had never been revealed by conventional oceanographic data. A front between an oceanic water mass and a polluted water mass runs in a NW-SE direction in the central part of the Osaka Bay. The patterns of turbid water discharged from the Kii River and Yoshino River show a northward tidal current in the North Kii Straits. The pattern of lighter turbid or polluted water located in the northwest region of the North Kii straits suggests the existence of a clockwise eddy in the straits.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: A flight test was conducted to determine the optimum exposures for the Skylab S-190A experiment. An aircraft multispectral photographic system (AMPS) which is installed in the NASA Earth Resources aircraft NP3A was used to simulate the S-190A system. The same film emulsions to be used for S-190A were used in the flight test. These rolls were on factory-loaded spools for use in the AMPS camera system. It was found that some variation is to be expected between these rolls and the S-190A flight loads.

Beschreibung: The basic elements of a cost-benefit study are discussed along with special considerations for ERTS experiments. Elements required for a complete economic analysis of ERTS are considered to be: statement of objectives, specification of assumptions, enumeration of system alternatives, benefit analysis, cost analysis nonefficiency considerations, and final system selection. A hypothetical cost-benefit example is presented with the assumed objective of an increase in remote sensing surveys of grazing lands to better utilize available forage to lower meat prices.

Beschreibung: The performance characteristics of the radar section of the prototype 4-8 GHz Microwave Active and Passive Spectrometer system are reported. Active and passive spectral responses were measured of natural, cultivated, and human-made surfaces over the 4-18 GHz region of frequencies for look angles between zero and 70 degrees and for all possible linear polarization combinations. Soil and plant samples were collected to measure their dielectric properties and moisture content. The FORTRAN program for area calculation is provided.

Beschreibung: A short-term technical study was performed by the MSC Earth Observations Division to determine the feasibility of the proposed Agricultural Stabilization and Conservation Service Automatic Remote Sensing/Compliance Determination System. For the study, the term automatic was interpreted as applying to an automated remote-sensing system that includes data acquisition, processing, and management.

Beschreibung: Detailed analyses are given of the performance of systems and subsystems on board ERTS-1 during orbits 2600-3810.

Beschreibung: The author has identified the following significant results. ERTS-1 has proven to be an effective earth-orbiting monitor of landscape change. Its regional coverage for large areal monitoring has been effective for the detection and mapping of agricultural plowing regions, for general forest cover mapping, for flood mapping, for strip mine mapping, and for short-lived precipitation mapping patterns. Paramount to the entire study has been the temporal coverage provided by ERTS. Without the cyclic coverage on an 18 day basis, temporal coverage would have been inadequate for the detection and mapping of strip mining landscape change, the analysis of agricultural landscape change based on plowing patterns, the analysis of urban-suburban growth changes, and the mapping of the Mississippi River floods. Cost benefits from ERTS are unquestionably superior to aircraft systems in regard to large regional coverage and cyclic temporal parameters. For the analysis of landscape change in large regions such as statewide areas or even areas of 10,000 square miles, ERTS is of cost benefit consideration. Not only does the cost of imagery favor ERTS but the reduction of man-hours using ERTS has been in the magnitude of 1:10.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: The author has identified the following significant results. In the Oriente area, well-drained forests containing commercially valuable hardwoods can be recognized confidently and delineated quickly on the ERTS imagery. In the tropical rainforest, ERTS can provide an abundance of inferential information about large scale geologic structures. ERTS imagery is better than normal aerial photography for recognizing linears. The imagery is particularly useful for updating maps of the distributary system of the Guagas River Basin and of any other river with a similarly rapid changing channel pattern.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: There are no author-identified significant results in this report.

Beschreibung: Calibration is a fundamental stage of the radiocarbon (14C) dating process if one is to derive meaningful calendar ages from samples’ 14C measurements. For the first time, the IntCal09 calibration curve (Reimer et al. 2009) provided an internationally ratified calibration data set across almost the complete range (0 to 50,000 cal BP) of the 14C timescale. However, only the last 12,550 cal yr of this record are composed of terrestrial data, leaving approximately three quarters of the 14C timescale necessarily calibrated via less secure, marine records (incorporating assumptions pertaining to the temporally variable “marine reservoir effect”). The predominantly annually laminated (varved) sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity to derive an extended terrestrial record of atmospheric 14C across the entire range of the method, through pairing of 14C measurements of terrestrial plant macrofossil samples (extracted from the sediment) with the independent chronology provided through counting of its annual laminations. This paper presents new data (182 14C determinations) from the upper (largely non-varved) 15 m of the Lake Suigetsu (SG06) sediment strata. These measurements provide evidence of excellent coherence between the Suigetsu 14C data and the IntCal09 calibration curve across the last ~12,000 cal yr (i.e. the portion of IntCal based entirely on terrestrial data). Such agreement demonstrates that terrestrial plant material picked from the Lake Suigetsu sediment provides a reliable archive of atmospheric 14C, and therefore supports the site as being capable of providing a high-resolution extension to the “wholly terrestrial” (i.e. non-reservoir-corrected) calibration curve beyond its present 12,550 cal BP limit.

Beschreibung: Scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold-and-thrust belt. The experimental set-up has two adjacent indenters moving in parallel with a velocity difference. The slow indenter moves with a relative velocity ranging from 40 to 80% of that of the fast one. In a first experimental series, quartz sand and low-friction glass beads represent the sediment stack and its basal detachment, respectively; silicone oil simulates a viscous detachment in the second series of experiments. The surface evolution and the spatio-temporal strain distribution are derived from particle image velocimetry (PIV). Together with the 3D finite structure derived by cutting the models at the end of each experiment, this allows the analysis of the structural evolution of the experimental wedges. Thrusting wedge development depends crucially on the relative velocity: when the slow indenter moves with a velocity of more than 55% of the fast indenter, a single curved thrust wedge develops. The wedge becomes decoupled along strike-slip zone at large velocity differences, i.e. when the slow indenter moves slower than 55% of the faster indenter. Consequently the thrust front is strongly curved at high (55–60%) and smoothly curved at low velocity differences (70–80%); in all cases curvature increases during indentation. Along the most strongly curved portion of the thrust wedge, the transfer zone rises, particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter. Thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter. Thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front. This implies distant effects of wedge growth active hundreds of kilometres along-strike of orogens. Silicone oil as a detachment induces a low-angle wedge, which is less curved than in the glass beads experiments, and shows variable thrust vergence with fore- and back-thrusts. We compare our experimental results with the curved fold-and-thrust belts of the Tajik basin in front of the Hindu-Kush and Pamir indenters; our results are able to explain several first-order features.

Beschreibung: Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities in the crust. In this study we used the P receiver function technique to investigate the velocity structure of the crust beneath the Northwest Zagros and Central Iran and map out the lateral variation of the Moho boundary within this area. Our dataset includes teleseismic data (Mb ≥ 5.5, epicentral distance from 30◦ to 95◦) recorded at 12 three component short-period stations of Kermanshah, Isfahan and Yazd telemetry seismic networks. Our results obtained from P receiver functions indicate clear Ps conversions at theMoho boundary. The Moho depths were firstly estimated from the delay time of the Moho converted phase relative to the direct P wave beneath each network. Then, we used the P receiver function inversion to find the properties of the Moho discontinuity such as depth and velocity contrast. Our results obtained from PRF are in good agreement with those obtained from the P receiver function modeling. We found an average Moho depth of about 42 km beneath the Northwest Zagros increasing toward the Sanandaj-Sirjan Metamorphic Zone and reaches 51 km, where two crusts (Zagros and Central Iran) are assumed to be superposed. The Moho depth decreases toward the Urmieh-Dokhtar Cenozoic volcanic belt and reaches 43 km beneath this area. We found a relatively flat Moho beneath the Central Iran where, the average crustal thickness is about 42 km. Our P receiver function modeling revealed a shear wave velocity of 3.6 km/s in the crust of Northwest Zagros and Central Iran increasing to 4.5 km/s beneath the Moho boundary. The average shear wave velocity in the crust of UDMA as SSZ is 3.6 km/s, which reaches to 4.0 km/s while in SSZ increases to 4.3 km/s beneath the Moho.

Beschreibung: Time variable gravity fields, reflecting variations of mass distribution in the system Earth is one of the key parameters to understand the changing Earth. Mass variations are caused either by redistribution of mass in, on or above the Earth's surface or by geophysical processes in the Earth's interior. The first set of observations of monthly variations of the Earth gravity field was provided by the US/German GRACE satellite mission beginning in 2002. This mission is still providing valuable information to the science community. However, as GRACE has outlived its expected lifetime, the geoscience community is currently seeking successor missions in order to maintain the long time series of climate change that was begun by GRACE. Several studies on science requirements and technical feasibility have been conducted in the recent years. These studies required a realistic model of the time variable gravity field in order to perform simulation studies on sensitivity of satellites and their instrumentation. This was the primary reason for the European Space Agency (ESA) to initiate a study on ''Monitoring and Modelling individual Sources of Mass Distribution and Transport in the Earth System by Means of Satellites''. The goal of this interdisciplinary study was to create as realistic as possible simulated time variable gravity fields based on coupled geophysical models, which could be used in the simulation processes in a controlled environment. For this purpose global atmosphere, ocean, continental hydrology and ice models were used. The coupling was performed by using consistent forcing throughout the models and by including water flow between the different domains of the Earth system. In addition gravity field changes due to solid Earth processes like continuous glacial isostatic adjustment (GIA) and a sudden earthquake with co-seismic and post-seismic signals were modelled. All individual model results were combined and converted to gravity field spherical harmonic series, which is the quantity commonly used to describe the Earth's global gravity field. The result of this study is a twelve-year time-series of 6-hourly time variable gravity field spherical harmonics up to degree and order 180 corresponding to a global spatial resolution of 1 degree in latitude and longitude. In this paper, we outline the input data sets and the process of combining these data sets into a coherent model of temporal gravity field changes. The resulting time series was used in some follow-on studies and is available to anybody interested.

Beschreibung: Im Rahmen der Klimapolitik wird die Lagerung von Kohlenstoffdioxid in tiefen Gesteinsschichten als eine potenzielle Maßnahme für die Reduktion der Treibhausgasemissionen und gegen die globale Klimaerwärmung gesehen. Mit dieser entwicklungsfähigen Technologie sind aber auch Ängste der Bevölkerung in den geplanten Zielgebieten verbunden: Ist eine langfristige und sichere Speicherung ohne Gefährdung des Menschen und der Umwelt möglich? Wissenschaft und Technik, unter besonderer Berücksichtigung der Erfahrungen vom Forschungsstandort Ketzin, helfen diese Frage zu beantworten.

Beschreibung: The studies of the 2004 and 2005 Sumatra earthquakes showed the presence of the segmentation boundary limiting the rupture areas offshore Northern Sumatra. Recent geophysical studies provide new insight on the structure of this boundary and the changes in the subduction processes around Northern Sumatra. In this study we present new model obtained from refraction/reflection seismic modeling, MCS data, and relocated seismicity. The comparison with the crustal scale profile located in the rupture area of the December 2004 Sumatra earthquake reveals principal differences in the structure of the accretionary complex, as well as in the structure of the forearc crust. The segmentation boundary is linked to the differences in the sediment supply at the trench and the variations in the Sumatra block crustal thickness. In the southern segment frontal prism is well developed and manifested in the clear trust faulting, it is separated from the accretionary prism by a pronounced splay fault, which are not clearly observed in the northern segment. The width of the accretionary complex is much narrower in the southern segment, while having similar depth extend. The Vp velocity analysis suggests that in the southern segment the Mentawai fault is active, while north of Simeulue it is not or less active. The crustal thickness of the Sumatra basement is increasing towards south, which influences the backstop geometry and the dip angle of the downgoing plate; resulting in the steeper subduction in the south.

Beschreibung: The climate change debate has increased the need for knowledge on both long- and short-term regional environmental changes. In general, these changes may often be a product of multiple causes, which complicates the separation of single driving forces. In this review we focus on current water budget changes in Germany’s capital region, Berlin-Brandenburg, over the last 30 years. Available studies from a variety of disciplines (e.g. hydrology, water engineering, landscape ecology, nature conservation) were analysed in order to (1) identify both local and regional hydrological changes, (2) reveal their potential causes, and (3) discuss responses of ecosystems and society. These studies show that the Berlin-Brandenburg region is widely characterised by decreasing groundwater recharge, leading to decreasing groundwater and lake levels as well as decreasing fluvial discharge. These trends result both from complex, regional human impacts (e.g. long-term effects of hydro-melioration and changes in forest composition) and more general climate warming. The observed and assumed (future) changes of the regional water balance have been creating, and will continue to create, multifaceted impacts on existing ecosystems and society (e.g. wetland drying, decrease of biodiversity, decrease of productivity of grasslands and forests, increasing conflicts of interests). Several efforts to respond to the regional water deficit problem have already been undertaken, comprising for instance land-use optimisation, wetland restoration measures and the reestablishment of mixed deciduous forests. In general, however, the reviewed regional material on this topic reveals that the number and complexity of empirical studies are still poor. Thus, for both the identification and the explanation of current water balance changes and their effects, as well as for development and implementation of adaptive strategies, further multidisciplinary research efforts at different scales, including interregional comparisons, are required. Furthermore, both the observation of hydrological changes and the evaluation of adaptive and mitigative responses require at least continuous or, even better, extended monitoring efforts.

Beschreibung: Core samples of the Upper Triassic (Keuper) Stuttgart Formation from the Ketzin pilot storage site have been experimentally treated with CO2. The major objective of the experimental program was to investigate the effects of long-term CO2 exposure on the mineralogical and petrophysical properties of the target formation.

Beschreibung: Heat entering large ice sheets and glaciers from the underlying bedrock controls the thermal regime of the basal ice layers in terms of basal melting, the formation of basal temperate ice layers and its influence on sliding processes. In this study, we estimate the effect of the uncertainties in geothermal heat flux (GHF) on the topography, dynamics and basal thermal conditions of simulations of the present-day Greenland Ice Sheet (GIS), using the dynamic polythermal ice-sheet model SICOPOLIS. Today’s GHF at the base of the GIS has been measured at only the locations of the deepest ice cores. It should therefore be considered as highly uncertain forcing component for the dynamic modeling of the major part of the GIS. Three GHF models are applied as lithosphere boundary conditions driving a series of paleoclimatic simulations. The first is based on a 3-D global seismic model of the crust and upper mantle, constrained in regions where heat-flow measurements are available. The other two models are based on tectonic regionalization and a combination of tectonic regionalization and deep ice-core measurements. Although the tectonic regionalization model was originally taken as a starting point for both the seismic mantle/crust and tectonic/ice-core GHF models, the resulting heat flow distributions across the extent of the GIS differ significantly, not only by the mean values but also by their spatial patterns. As a consequence, the present-day GIS driven by the seismic GHF model is 450 meters thicker in the northern and central parts of the GIS, and 450 meters thinner in the southern part relative to the GIS forced by the tectonic/ice-core GHF model. In addition, the horizontal ice transport simulated using the seismic GHF model is 10-50% higher in the northern and western GIS, and 10-30% lower in the southern and eastern GIS than the transport resulting from the simulation driven by the tectonic/ice-core GHF model. These alterations in the GIS topography and horizontal transport induced by the two latter simulations with respect to the simulation driven by the tectonic regionalization model have the opposite tendencies. Finally, we discuss different scenarios of the evolution of the temperate base in the ice-sheet simulations driven by the seismic-based, tectonic regionalization and tectonic/ice-core GHF models. The modeled present-day temperate ice areas with non-zero basal melting cover 34%, 40.6% and 56.8% of the ice-covered area, respectively, for each of the GHF models examined. The minimum coverage of the temperate ice is reached shortly after the last glacial maximum and amounts to less than 20% of the ice-covered area, as determined using the seismic and tectonic GHF models, and about 40% when employing the tectonic/ice-core model. Although the response of the modeled ice-sheet to changing basal conditions may be influenced by the limitations in the classical polythermal approach used in SICOPOLIS (neglecting water diffusivity), we may conclude that the modeled present-day thermodynamical state of the GIS is largely sensitive to the GHF model employed

Beschreibung: Archeomagnetic results and high resolution sedimentary records have been used to reconstruct the global geomagnetic field for millennial time-scales. Here I present a series of models named CALSxk, Continuous models based on Archeomagnetic and Lake Sediment data of the past x kyrs, and in particular CALS10k.1b, the first regularized spherical harmonic field model for the past 10 kyrs. The effects of uncertainties in both magnetic elements and their ages and of uneven global data distribution are assessed by a bootstrap resampling scheme. I discuss the evolution of the dipole moment and tilt and features of the radial field component at the core-mantle boundary. The model also provides estimates for field directions and intensity for any location at Earth's surface. However, as the presently available data distribution is uneven and strongly biased towards the northern hemisphere and Europe in particular, the accuracy and resolution of global models remains limited. More high resolution lake or marine paleomagnetic sediment records and archeomagnetic results from from the southern hemisphere, e.g. the South American countries, are necessary to improve global field reconstructions.

Beschreibung: Observations of the ocean-induced magnetic field by the CHAMP magnetic space mission have the potential to be used as a constraint when examining ocean dynamics. This has initiated theoretical studies on the prediction of the ocean-induced magnetic field. These studies predict the poloidal magnetic field induced by the horizontal ocean-circulation flow by employing a single-layer approximation. Since the toroidal magnetic field cannot be modelled by this approximate model, we treat the ocean as a layer of finite thickness and model the toroidal magnetic field by a matrix-propagator technique with a source of electrical currents in the ocean layer. Although this primary toroidal magnetic field is not observable outside the oceans, it couples with a strong conductivity contrast between the oceans and continents and generates a secondary poloidal magnetic field. This field is observable by magnetic satellite missions and ground-based magnetic observatories situated close to the shoreline. Such constraints are expected to be improved upon by the launch in 2012 of the SWARM magnetic field observing satellites.

Beschreibung: Magnetic extracts obtained from sediment cores recovered from Lake Kinneret, Israel, were subjected to comprehensive scanning electron microscope and in-line energy dispersive X-ray spectroscopy analyses. A variety of ferrimagnetic iron oxides and iron sulphide particles were identified, along with apparently non-magnetic iron sulphides. The majority of the iron oxides are titanomagnetites that have undergone pervasive dissolution, and in many cases were only preserved as skeletal, 3-D lattices of ilmenite lamellae. Often the spaces between the submicron ilmenite lamellae are empty. Also sponge-like dissolution features are observed in some residual titanomagnetite grains. Another group of titanomagnetite grains is characterized by superficial shrinkage-cracks, which indicate low-temperature maghemitization. In some cases, these cracks appear to be where dissolution started. Most titanomagnetites contain impurities of Al, Mg, Si and Mn on the order of 1 per cent. Chromium-magnetites, with minor Ti, Mg and Al content on the order of a few percent, but without Mn, were also found. Chromium-magnetites mostly occur as octahedra in a well-preserved state, which indicates that they are less prone to dissolution. Magnetite spherules of 40–60 μm in size, which were mostly hollow, were only found in material collected from the outer zone of the core section that was in contact with the steel core barrel. These spherules were not found in material collected from the centre of the core. They are therefore interpreted as contaminants that were produced during fabrication of the steel core barrel. Iron sulphides are present as pyrite, either as larger aggregates of cubic crystals, each of up to 20 μm in size, or as 5–10 μm framboidal aggregates, consisting mostly about 0.3 μm idiomorphic octahedra. The cubic pyrite crystals have heterogeneous compositions. Pure pyrite should be non-magnetic, but even aggregates of up to 150 μm in size were magnetically separated. They probably therefore contain a magnetic core of greigite or overgrown titanomagnetite. The latter possibility is supported by observations of residual titanomagnetites with individual pyrite crystals residing directly on their surfaces, or filling space between ilmenite lamellae. Irregular aggregates of flaky, submicron iron sulphides were also found, which are interpreted to be greigite. The greigite has a low degree of visible crystallization. Pyrite and/or greigite grains were found inside the aggregates, or in agglomerates with organic remnants. Together, visual observations and elemental analyses provide clear evidence of pervasive dissolution of primary titanomagnetite and concurrent sulphidization of sediments from Lake Kinneret.

Beschreibung: Results obtained from S and P receiver functions produced a clear image of the top and bottom of the subducting Nazca lithosphere beneath northern Chile. Using data from the teleseismic events recorded at 15 permanent Integrated Plate Boundary Observatory Chile (IPOC) stations, we obtained new constraints on the geometry and thickness of the descending Nazca lithosphere. We observed the subducted crust of the Nazca plate at depths ranging from 50 km beneath the Coastal Cordillera down to 110 km beneath the Western Cordillera. We found significant along‐strike variations in the geometry of the Nazca plate beneath northern Chile. On closer inspection, it appears that the oceanic Nazca plate is divided into two distinct segments as it descends beneath the continental South American plate. The transition from the relatively steeper (∼23°) and deeper slab to the north of 21°S to the flatter southern segment (∼19°) is shown reasonably clearly by our data. This feature could well be associated with variations in the curvature of the plate margin and the geometry of the Chile trench, which is mainly curved to the north of 21°S. We have also mapped the continental Moho of the South American plate at depths ranging between 60 and 70 km to the east of the Longitudinal Valley. Beneath the Coastal Cordillera, this boundary becomes invisible, probably due to the serpentinization of the forearc mantle wedge that reduces the velocity in the uppermost mantle. The base of the subducted Nazca plate was clearly identified as a sharp boundary in the results obtained from the P and S receiver functions. The thickness of the subducted oceanic Nazca plate, which has an age of ∼50 My, is estimated to be ∼50 km. Although this thickness is consistent with that predicted by thermal gradients, the explanation of the sharpness of the lithosphere‐asthenosphere boundary may require another mechanism such as hydration or melting.