Several Tens Of Centimeters Research Articles

TRUQ (TRansformation-Heat based up-quenching) for high-performance Nb/sub 3/Al superconductors

Heat treatment conditions and procedures of the transformation-heat based up-quenching (TRUQ) process particular to Nb/sub 3/Al coils are studied. It is found that pre-heating at 600/spl deg/C before TRUQ process makes the bcc phase ordered but does not cause transformation. Noticeable is that TRUQ process combined with such a pre-heating does not depress the J/sub c/ performance, compared with TRUQ process without pre-heating. Thus, pre-heating before TRUQ process can be used to help fast-heating of coils. In this work, a vacuum furnace having two heaters or a set of fluidized-bed furnaces are used for TRUQ process combined with pre-heating. Samples used are small coils where the conductor of several tens of centimeters in length is wound on a stainless-steel bobbin. It is found that both ways improve J/sub c/ characteristics, compared with the conventional transformation process. Additionally, untransformed short samples are ohmically heated as TRUQ process, controlling current or voltage of the power supply, to control the application of the ohmic-heating to provide a practical coil heat treatment.

Changes in the spatial structure of the destruction process under the conditions of atmospheric pollution of forest ecosystems

Contamination of the southern taiga forests (Middle Urals) by discharges from cooper smelters (heavy metals combined with SO2) not only decreases the mean rate of decomposition of pure cellulose, but also radically changes the spatial structure of the destruction process. Heterogeneity of distribution of the destruction rate is sharply increased near the source of discharge due to differentiation of the space into microregions with high and low destruction rates. The characteristic size of spatial heterogeneity amounts to several tens of centimeters and the distribution of microregions with a high rate is accidental within several tens of meters. A hypothesis has been put forward that the described changes in the spatial structure of the destruction process are related, above all, to disturbed colonization of the substrate by soil myxomycetes.

Reconciling Extreme‐Ultraviolet and Radio Observations of the Sun’s Corona

The Sun's corona, which is composed of plasma at a temperature of a few millions of degrees, can be best viewed in two electromagnetic domains, one from wavelengths of a few angstroms to hundreds of angstroms (in the soft X-ray and EUV domain), the other from wavelengths of a few centimeters to several tens of centimeters (in the radio domain). In this paper, we present a quantitative comparison of coronal observations made in these two domains with high spatial resolution over the full disk of the Sun. The EUV observations were taken with the EIT (Extreme-Ultraviolet Imaging Telescope) on board SOHO (Solar and Heliospheric Observatory), and the radio observations were taken with the VLA (Very Large Array). The two sets of images show very similar morphologies, indicating that the different wavelengths originate from common solar features. We predict radio fluxes using the temperature and emission measure of the corona calculated from EIT observations, adopting Meyer's table of coronal abundances for the calculations. In each of the seven observations investigated, there always exists a good linear correlation in the pixel-by-pixel correlation plot between the predicted and the observed radio flux for coronal features over a wide range of flux variation. Nevertheless, the predicted radio flux is systematically larger than that observed by a factor of 2.0 ± 0.2, on average. We attribute the difference to the underestimation of the abundance of Fe relative to H in the abundances adopted by Meyer. On this basis, we place the absolute Fe abundance in the corona at 7.8 × 10-5, which has an enrichment factor of 2.4 relative to the accepted photospheric Fe abundance.

Characteristic length of fuel and oxygen consumption in feed channels of polymer electrolyte fuel cells

How much of feed channels is actually used in a fuel cell? This problem is considered in this paper where we study gas or liquid feed consumption in the feed supplying channels of a polymer electrolyte fuel cell. Simple analytical expressions which define profiles of feed concentration along the channel and expressions for characteristic length of feed consumption are obtained. For typical conditions this length could be as low as several tens of centimeters. The dependence of consumption length on reaction rate parameters and system parameters is discussed. Analytical results are in good agreement with data of simulation, performed specially to verify the validity of the theory.

WARBLE: A high resolution approach to subbottom geoacoustic inversion

Subbottom geoacoustic information supports a broad range of activities serving military, scientific, and commercial needs. Since direct sampling (i.e., coring) of the seabed is costly and time-consuming, numerous acoustic inverse methods have been developed. One of the most serious weaknesses, which is suffered by all the inversion methods, is a uniqueness problem, wherein multiple solutions fit the data equally well. An associated problem is that some methods have no means to determine the number of sediment layers in the solution space. Our WARBLE (wide-angle reflection and bottom loss experiment) method addresses these problems by conducting the inversion in both the space-time and the space-frequency domains in order to maximize the amount of independent data. The space-time data provide the number of important layers as well as the layer thicknesses, and interval sound speeds. The space-frequency domain data provide sound velocity, density, and attenuation for each layer. High-resolution results can be obtained with this method, resulting in layer thickness of order several tens of centimeters. Penetration depends upon sediment type and water depth but is typically 50–150 m. The inversion method will be illustrated with several shallow-water measurement/inversion results, including comparisons with core data.

Influence of lithospheric and mantle stratification on co- and�post-seismic deformation due to finite faults

Coseismic and post-seismic deformation in the fully relaxed state following large earthquakes is modelled for finite faults by means of multilayered, viscoelastic, self-gravitating, hydrostatically pre-stressed, spherical earth models based on the preliminary reference earth model (PREM) with a Maxwell rheology. For both finite dip-slip and strike-slip sources we find that the elastic layering of the lithosphere has a major impact on the modelling of co- and post-seismic deformation. For large and deep earthquakes embedded at the base of the lithosphere in the proximity of the lithosphere–upper mantle interface in order to study the effects of mantle relaxation, coseismic and post-seismic deformation can result in several tens of centimetres of displacement, with a deformation pattern strongly dependent on the distance from the source and the azimuth from the strike of the fault. Strike-slip faulting is found to be more sensitive to mantle rheology than dip-slip faulting. Deviations between earth models with a homogeneous crust and lithosphere and those based on PREM are of the same order as the coseismic and post-seismic signals, ranging from a few centimetres to several tens of centimetres for large earthquakes with seismic moments of 1022 N m and epicentral depths of 75–100 km at the base of the lithosphere. This finding lends further support to the conclusion of a preliminary study based on dip-slip point sources that observations based on VLBI, GPS and SAR techniques, which can easily resolve crustal deformation of the order of the deviations among the various lithospheric models, can be badly misinterpreted if the results of surveying in seismogenic regions are compared with earth models that have a limited number of layers in general and a homogeneous crust in particular.

Surficial slip distribution on the central Emerson fault during the June 28, 1992, Landers earthquake, California

We present the results of our mapping of a 5.6‐km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right‐lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right‐lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left‐lateral or thrust displacement. The maximum net vertical displacement was 175 cm, east‐side‐up. The sense of vertical slip across the main fault zone varied along strike, but in most cases it was consistent with the sense of vertical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variations in surficial slip have been reported along previous strike‐slip ruptures, our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously. We document variations in slip as large as 1 m or more over distances ranging from 1–2 km to a few tens of meters, suggesting that strains of the order of 10−1may have occurred locally within the surficial sediments. The long‐wavelength (kilometer‐scale) variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments. The slip variations over shorter length scales (tens of meters) may be caused by variations in the proportion of the total shear that occurs on visible, brittle fractures versus that which occurs as distributed shear, warping or rotation. The variability of slip along the ruptures associated with the Landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures.

The determination of ice composition with instruments on cometary landers

The determination of the composition of materials that make up comets is essential in trying to understand the origin of these primitive objects. The ices especially could be made in several different astrophysical settings including the solar nebula, protosatellite nebulae of the giant planets, and giant molecular clouds that predate the formation of the solar system. Each of these environments makes different ices with different composition. In order to understand the origin of comets, one needs to determine the composition of each of the ice phases. For example, it is of interest to know that comets contain carbon monoxide, CO, but it is much more important to know how much of it is a pure solid phase, is trapped in clathrate hydrates, or is adsorbed on amorphous water ice. In addition, knowledge of the isotopic composition of the constituents will help determine the process that formed the compounds. Finally, it is important to understand the bulk elemental composition of the nucleus. When these data are compared with solar abundances, they put strong constraints on the macro-scale processes that formed the comet. A differential scanning calorimeter (DSC) and an evolved-gas analyzer (EGA) will make the necessary association between molecular constituents and their host phases. This combination of instruments takes a small (tens of mg) sample of the comet and slowly heats it in a sealed oven. As the temperature is raised, the DSC precisely measures the heat required, and delivers the gases to the EGA. Changes in the heat required to raise the temperature at a controlled rate are used to identify phase transitions, e.g., crystallization of amorphous ice or melting of hexagonal ice, and the EGA correlates the gases released with the phase transition. The EGA consists of two mass spectrometers run in tandem. The first mass spectrometer is a magnetic-sector ion-momentum analyzer (MAG), and the second is an electrostatic time-of-flight analyzer (TOF). The TOF acts as a detector for the MAG and serves to resolve ambiguities between fragments of similar mass such as CO and N 2. Because most of the compounds of interest for the volatile ices are simple, a gas Chromatograph is not needed and thus more integration time is available to determine isotopic ratios. A gamma-ray spectrometer (GRS) will determine the elemental abundances of the bulk cometary material by determining the flux of gamma rays produced from the interaction of the cometary material with cosmic-ray produced neutrons. Because the gamma rays can penetrate a distance of several tens of centimeters, a large volume of material is analyzed. The measured composition is, therefore, much more likely to be representative of the bulk comet than a very small sample that might have lost some of its volatiles. Making these measurements on a lander offers substantial advantages over trying to address similar objectives from an orbiter. For example, an orbiter instrument can determine the presence and isotopic composition of CO in the cometary coma, but only a lander can determine the phase(s) in which the CO is located and separately determine the isotopic composition of each reservoir of CO. The bulk composition of the nucleus might be constrained from separate orbiter analyses of dust and gas in the coma, but the result will be very model dependent, as the ratio of gas to dust in the comet will vary and will not necessarily be equal to the bulk value.

Possible Effect of Kelvin-Helmholtz Instability on VHF Radar Observations of the Mean Vertical Wind

Mean vertical velocities are of great interest in meteorology and vertically directed VHF radar have been used to measure directly. Recently it has been pointed out that in a gravity wave with upward energy propagation the radar reflectivity and the vertical velocity are negatively correlated, giving rise to a downward bias for the observed . In the present paper, it is shown that in regions of Kelvin-Helmholtz instability (KHI) the correlation between refractivity-surface tilting angles and the (apparent) vertical velocity observed with a vertically pointing VHF radar can lead to a bias with magnitudes of several tens of centimeters per second. This “KHI bias” is upward in the shear zone above the horizontal wind speed maximum of a jet stream and downward below. Theoretical vertical profiles of the predicted KHI bias exhibit considerable similarity with profiles observed during jet stream events by other authors, suggesting that a major part of the observed might be attributable to the presumed KHI bias.

Pyroclastic flows and surges over water: an example from the 1883 Krakatau eruption

Pyroclastic deposits from the 1883 eruption of Krakatau are described from areas northeast of the volcano on the islands of Sebesi, Sebuku, and Lagoendi, and the southeast coast of Sumatra. Massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km. Granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the Krakatau islands. The distal deposits exhibit a decrease in sorting coefficient, median grain size, and thickness with increasing distance from Krakatau. Crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards. The deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 August at approximately 10 a.m. Energetic flows spread out away from the volcano at speeds in excess of 100 km/h and traveled up to 80 km from source. The flows retained temperatures high enough to burn victims on the SW coast of Sumatra. Historical accounts from ships in the Sunda Straits constrain the area affected by the flows to a minimum of 4x103 km2. At the distal edge of this area the flows were relatively dilute and turbulent, yet carried enough material to deposit several tens of centimeters of tephra. The great mobility of the Krakatau flows from the 10 a.m. activity may be the result of enhanced runout over the sea. It is proposed that the generation of steam at the flow/seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective. The buoyant distal edge of these ash-and steam-laden clouds lifted off into the atmosphere, leading to cooling, condensation, and mud rain.

Performance characterization of rf-driven multicusp ion sources

Radio-frequency (rf)-driven multicusp ion sources have been developed extensively at Lawrence Berkeley National Laboratory (LBNL) for many applications, each requiring specific source designs. These uses have ranged from large ion sources for neutral-beam injectors—several tens of centimeters in size—to small sources for oil-well logging neutron tubes—a few centimeters in diameter. The advantages associated with internal antenna, rf-driven ion sources include reliability, long component life, ease of operation, and the ability to generate plasmas free of the impurities commonly found in hot-filament discharge sources. We have investigated and characterized the performance of rf-driven sources with respect to the rf operating frequency and ion source size for hydrogen ion species and current density. Furthermore, we have included in this study the aspects of proper coupling of the rf generator to the antenna through an impedance matching network. Finally, critical issues pertaining to general rf operation including beam extraction, rf shielding, and cooling of transformer cores are discussed.

Estimating the sea surface dynamic topography from Geosat altimetry data

Optimal interpolation method is applied to Geosat altimetry data both to remove orbit error and to separate temporal mean sea surface dynamic topography (SSDT) from temporal fluctuations around the mean. Loss of long-wavelength oceanic signals at orbit error reduction procedure is smaller in this method than that in conventional collinear methods, but the areal average height over the study domain is still removed as the orbit error. The fluctuation SSDT is quantitatively evaluated by sea level data from tide gauge stations at Japanese islands. The correlation coefficient of the two sea-level variations is 0.83 when the loss of the areal average is compensated by the seasonal variation of the areal average height determined from the climatological monthly-mean SSDT. In addition, the improvement of the geoid model by combined use of Seasat altimetry data and hydrographic data is validated through the estimated temporal mean SSDT. In a local area where hydrographic data contemporary with the Seasat mission exist, the geoid model has been significantly improved so that the absolute SSDT can be determined from combination of the altimetry data and geoid model; the absolute SSDT describes the onset event of a quasi-stationary large meander of the Kuroshio south of Japan very well. Outside this local area, however, errors of several tens of centimeters still remain in the improved geoid model.

North Atlantic deep-sea sedimentation of Late Quaternary tephra from the Iceland hotspot

Piston cores recovered from the North Atlantic were used to study the sedimentation of Holocene and Pleistocene volcanic ash in the Irminger and Iceland Basins. Ash Zones 1 (≈ 11,100 yr B.P.), 2 (≈ 55,000 yr B.P.) and 3 (≈ 305,000 yr B.P.) were identified from their major element glass composition. The silicic and alkalic Ash Zones 1 and 2 originate from the Southeastern Volcanic Zone of Iceland, where they correlate with the Sólheimar ignimbrite from Katla volcano and the Thórsmörk ignimbrite from Tindfjallajökull volcano, respectively. The low-alkali composition of silicic Ash Zone 3 indicates a source from one of the silicic centers in the active rift system. Ash Zones 2 and 3 occur in the Irminger Basin as dispersed glass shards over a depth interval of several tens of centimeters. Their compositional and granulometric characteristics reflect an initial fallout on pack-ice north of Iceland, followed by ice-rafting sedimentation in the Denmark Strait, prior to bioturbation. δ 18O stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval, at the time when seas north of Iceland were ice-covered. Sedimentary features indicate that turbidity currents were also involved in the dispersal of Ash Zones 1 and 2 south of Iceland. The initiation of these gravity currents from the shelf can be attributed to either glacier bursts (jökulhlaups) carrying tephra, or the entrance of pyroclastic flows into the ocean.

Lateral Continuity of Facies and Parasequences in Middle Cambrian Platform Carbonates, Carrara Formation, Southeastern California, U.S.A.

ABSTRACT Lateral and vertical changes within a 40-m-thick interval of peritidal carbonates (Middle Cambrian Jangle Limestone Member, Carrara Formation, SE California) produce a mosaic pattern of laterally continuous and discontinuous facies, shallowing-upward cycles 2-20 m thick (parasequences), and surfaces bounding parasequences. This mosaic pattern was traced, bed by bed, across 1.8 km of continuously exposed outcrop, and then correlated to sections in nearby ranges. Within parasequences, contacts between successive subtidal facies tend to be sharp but may pass laterally into gradational contacts. Most subtidal facies extend laterally for less than 300 m, passing gradationally (over tens of centimeters to meters) into other, laterally adjacent subtidal facies. Lateral facies contacts between subtidal nodular ribbon rock and intertidal fenestral limestone are gradual over a few meters, whereas contacts between vertically juxtaposed facies generally are sharp. Parasequence boundaries generally are sharp and locally show several tens of centimeters of erosional relief over lateral distances of several meters. Most parasequences and their bounding surfaces extend for the 1.8 km of outcrop studied and correlate to nearby ranges with varying degrees of confidence. Several parasequences, however, do not extend laterally for more than a few hundred meters and are not distinguishable in a vertical profile from those that extend laterally for tens of kilometers. The stratigraphic relationships at Eagle Mountain (southeastern California) support a model in which the lateral continuity of parasequence surfaces is principally determined by accommodation variations, and the lateral continuity of facies is most strongly influenced by the intrinsic dynamics of spatially and temporally heterogeneous sediment production. The presence of parasequence boundaries of highly variable lateral extent suggests that the magnitude of accommodation variations was comparatively small, consistent with the independent evidence for passive-margin subsidence and transitional greenhouse conditions for the Middle Cambrian.

Photon Splitting in Strongly Magnetized Cosmic Objects—Revisited

We reassess the importance of photon splitting to spectral formation in cosmic X-ray and $\gamma$-ray sources with magnetic fields of several $10^{12}$ gauss. Our analysis is based on the recent numerically accurate evaluation of the full relativistic expression for photon splitting at neutron star magnetic field strengths (Mentzel et al. 1994). Using these results we demonstrate that Adler's (1971) widely used approximation formula for photon splitting underestimates the correct splitting rate by {\em several} orders of magnitude, at these magnetic field strengths. Even down at X-ray energies of a few tens of keV magnetic photon splitting is found to be an efficient photon conversion process, producing mean free paths as short as several tens of centimeters for fields on the order of $5 \times 10^{12}$ gauss. We conclude that previous analyses of the contributions of magnetic photon splitting to spectral formation based on Adler's approximation formula are physically unreliable, and, in particular, that photon splitting must be included in realistic modelings of spectra of both strongly magnetized cosmic X-ray and $\gamma$-ray sources.

Chaotic obliquity and the nature of the Martian climate

Recent calculations of the Martian obliquity suggest that it varies chaotically on timescales longer than about 107 years and varies between about 0 and 60°. We examine the seasonal water behavior at obliquities between 40 and 60°. Up to several tens of centimeters of water may sublime from the polar caps each year, and possibly move to the equator, where it is more stable. CO2 frost and CO2‐H2O clathrate hydrate are stable in the polar deposits below a few tens of meters depth, so that the polar cap could contain a significant CO2 reservoir. If CO2 is present, it could be left over from the early history of Mars; also, it could be released into the atmosphere during periods of high obliquity, causing occasional periods of more‐clement climate.

Soil measurements by nuclear track detectors

In characterization of soil contaminated by transuranics or actinides, some one would be interested in both horizontal and depth distributions. Nuclear Track Detectors (NTD's) are an excellent tool for making inexpensive in-situ measurements. The activity and spatial distribution of such alpha emitting radionuclides as plutonium, americium, and uranium, can be determined. This paper will focus on the methodology for surface mapping and depth profiling of alpha contaminants. The detector material is CR-39. The plastic detectors are placed directly on the soil surface to be measured or inserted into the soil at the measurement point. The detectors may be wedged into a hole punched into the ground or driven into the ground inside of a protective rod. After exposure, the plastic is retrieved, washed with water, and chemically etched overnight in a KOH solution. The lengthwise distribution of etch tracks along the strip is measured to produce a depth profile of the alpha activity. With this methodology it is possible to measure activities below a few Bq per gram, identify hot spots with submillimeter accuracy, and profile distributions to depths of several tens of centimeters. The in-situ measurements produce no radioactive waste and are very low in cost compared to radiochemical methods of analysis.

Optical feedback displacement sensor using a laser diode and its performance improvement

We propose a new compact interferometric sensor for displacement measurement which utilizes the output intensity undulation caused by the optical feedback effect of a frequency modulated laser diode (LD). In order to stabilize the undulation signal, the relationship between the feedback rate and the oscillation behaviour of the LD was investigated experimentally. The results revealed that the undesired higher order undulation could be suppressed by a low feedback rate. In addition, a new current modulation technique for the LD was developed for improving the performance of the signal processing based on a pseudo-heterodyne scheme. By these improvements, the measurement range was extended to several tens of centimetres with resolution of under 25 nm. Two sensor systems were combined for the measurement of a two-dimensional displacement of a spherical retro-reflector.

Palaeomagnetic reorientation of cores and the magnetic fabric of hydrocarbon reservoir sands

Abstract The palaeomagnetic method is established as an important complement to more traditional methods for reorienting cores drilled in hydrocarbon exploration and production programmes. The method is based on the isolation of one or more components of remanent magnetization within the core. These provide records of the direction of magnetic north, either for recent times (carried by magnetic overprints in the recent geomagnetic field at the drill site) or at the time of formation of the sediment (carried by the primary magnetization). Provided that any spurious components of magnetization associated with drilling are removed by appropriate analysis in the palaeomagnetism laboratory, then the magnetic components of interest can be separately isolated. The mean direction of stable remanent magnetization, averaged over several tens of centimetres of core, defines the direction of geographical north in that core section. For a recent component, the direction of north is specified directly, whereas for an ancient component this is given by reference to the direction predicted from published apparent polar wander curves for that plate or geographical region. An important attribute of the palaeomagnetic core reorientation method is that the measurements are made on samples from the cores themselves, rather than by downhole instruments such as multishot orientation tools, dipmeters or imaging tools. This makes the technique particularly cost-effective and frees it from reliance on the proper performance of downhole tools or the correlation of planar features observed in the cores with those in the well. Consequently, there is no requirement for the well to be deviated or for there to be a significant natural dip to the formation (although this does help in fitting adjacent core pieces together to allow extrapolation of the reorientation data to longer intervals of core). Furthermore, as the determinations are made directly on the cores, the precision of palaeomagnetic reorientation is inherently greater than for methods based on measurements made in the well. It is possible to apply the method to cores for which the need for orientation was not apparent at the time of drilling, but for which this need arises as a result of later developments. The technique can be applied equally well to recently drilled cores or cores which have been stored for many years. An account is given of the palaeomagnetic reorientation method and its applications to (1) defining fracture orientations and (2) establishing sediment transport directions in a channel sand body. The transport directions are inferred from magnetic fabric measurements and the principles of the anisotropy of magnetic susceptibility technique are briefly reviewed.

Slope-shelf-nearshore depositional sequences with transgressive conglomerate in a Miocene backarc and arc-junction setting, central Japan

Several third-order slope-shelf-nearshore depositional sequences are found in the Middle to Late Miocene Aoki and Ogawa Formations in the southern part of the Northern Fossa Magna region, central Japan. Each depositional sequence consists of a transgressive systems tract, varying in thickness from several tens of centimetres to about 10 m, a falling stage systems tract several tens of metres in thickness and a highstand systems tract, 20–80 m thick. The highstand systems tract and falling stage systems tract are bounded by the regressive surface of marine erosion. Each depositional sequence mainly consists of coarse-grained sediments. The materials of the transgressive conglomerate beds were derived from the gravelly foreshore and upper shoreface by transgressive shoreface erosion. The thin and conglomeratic transgressive systems tract indicates that these slope-shelf-nearshore sequences were deposited on the steep slope area under a rapid transgression. Therefore, these sequences were formed in response to excess sediment supply and a rapid rise in relative sea-level at an active margin of the backarc side of the arc-trench system.