Trench Region Research Articles

Stress changes and aftershock distribution of the 1994 and 2006 Java subduction zone earthquake sequences

[1] The Mw = 7.8 1994 and the Mw = 7.7 2006 interplate thrust mechanism earthquakes that occurred in the Java subduction zone produced dominantly normal-faulting aftershocks, unusual for large megathrust main shocks. Various models proposed for these earthquake sequences invoke main shock rupture on an isolated portion of a decoupled plate boundary fault, with updip and outer-rise extension leading to the normal faulting. Other models suggest that these aftershocks occurred in a zone of the subduction zone where usually earthquakes cannot propagate or initiate, leading to the occurrence of normal-faulting aftershocks in the outer rise, overriding and subducting plates. Here we examine a simpler possibility, one in which Coulomb stress changes (ΔCFS) imparted by slip during the two large subduction events led to normal-faulting events on favorably oriented planes within the slab and near trench region of the subduction zone. We compute stress changes resulting from both events and subsequent large aftershocks using both uniform and variable slip models for main shock slip, resolved onto both aftershock nodal planes. We find that there is not a clear pattern of aftershock occurrence in areas of stress increase due to main shock slip. This implies that these aftershocks are not simply triggered by the static stress changes from the main shock and additional complexity should be considered to explain these unusual earthquake sequences.

Mantle phases recorded at Guam for distances between I" and 52"

An analysis of P and S arrivals recorded at Guam from 175 earthquakes which occurred along the seismic belt in the Western Pacific reveals differences between the travel times to that station and those recorded at Marcus, Midway, and Wake islands from earthquakes occurring in the same general area. Three possible explanations are offered to account for the observed discrepancies: (1) eompressional phases observed at Marcus, Midway, and Wake are mantle-guided phases of the Pn type; (2) systematic errors in epicenter determinations of the type reported by Japanese authors for earthquakes in the Kurile, Japan, and Izu trench region are present; and (3) real differences exist in the upper-mantle velocity structure of the two regions in question through which the phases travelled. Either of the last two hypotheses is considered more acceptable than the first. The travel times to Guam are found to be similar for earthquakes north and south of the station, but for earthquakes to the north at distances greater than ~ 26°, energy being transmitted to Guam appears to be absorbed or blocked. This may be explained by a high attenuation zone along paths sub-parallel to the Marianas, Izu, Japan, Kurile trenelis or by a shadow zone at Guam produced by the lateral refraction of energy by the downgoing lithospheric slab.

Defect structure originating from threading dislocations within the GaN film grown on a convex patterned sapphire substrate

We investigated defect structures in the GaN film grown on a convex patterned sapphire substrate (CPSS) to determine the origin of structural improvement by transmission electron microscopy (TEM) and laser confocal scanning microscopy (LCSM). From the TEM results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. Also the staircase-like TDs were observed near the curved slant region of the convex pattern; they converged at the top of the convex patterned region by staircase-upward propagation. This scenario seems to effectively prevent TDs from vertical propagation in the trench region. The photoluminescence mapping and spectra obtained by LCSM are consistent with these results from TEM observations. The generation of staircase-like TDs relates to the formation of a terraced surface during the growth, and suggests a probable mechanism that changes the propagation direction of TDs via the curved surface of the CPSS. The lateral growth and staircase-upward propagation of TDs are major factors on structural improvement of the GaN film grown on CPSS.

Low Dose Rate Effects in Shallow Trench Isolation Regions

Dose-rate effects are studied in shallow trench isolation regions. Increased damage is observed at low dose rate, with a different dose dependence compared to tests done at high dose rate. A three-dimensional modeling program was used to show that charge trapping occurs much deeper in the trench region when sufficient charge is present to reduce the field in the trench.

Spatial stress distribution and optical properties of GaN films grown on convex shape-patterned sapphire substrate by metalorganic chemical vapor deposition

μ-Raman and μ-photoluminescence methods have been employed to investigate microscopic spatial stress distribution and optical properties of GaN films grown on the convex shape-patterned sapphire substrate (CSPSS). By comparison of the μ-Raman and μ-PL spectra, we found that significantly large difference, Δ σ xx ∼0.46 GPa, in biaxial compressive stress between the flat trench and convex regions in the side facet of the GaN film, around ∼2 μm below the surface whereas on the GaN surface, little difference with large residual stress was observed in both regions compared to those from the side facet. Temperature dependent and time-resolved photoluminescence spectra have shown that the GaN film grown on the CSPSS has improved crystal purity through the reduction of intrinsic point defects.

Multi-proxy records of regionally-sourced tsunamis, New Zealand

A multi-proxy study of sediment cores from Kaituna Bay, Mimiwhangata, in northern New Zealand has produced a record of three palaeotsunamis, dated to around 6500 cal yr BP, 2800 cal yr BP, and 1450 AD. These events punctuate a coastal palaeoenvironmental history spanning the last 8000 years or more in which the site progressed from a semi-open lagoon to a freshwater swamp. Proxies used included stratigraphy, geochemistry, palynology, diatoms, foraminifera, geomorphology, and a regional palaeotsunami synthesis. The identification of tsunamigenic sources for these events is tentative. We propose that the two oldest events are associated with a source in the Tonga–Kermadec Trench region, with the most recent possibly associated with the Kuwae caldera collapse in 1452/1453 AD. Palaeotsunami deposits contemporaneous with the estimated age of the three events identified in this study were used to assist in identifying possible source regions. The development of regional and national palaeotsunami databases is in its infancy, but as more data become available, the ability to determine the source, magnitude and frequency of past events will improve. This will greatly enhance our understanding of the regional risk from tsunamis.

Dynamic distributed drainage implied by the flow evolution of the 1996–1998 Adventure Trench subglacial lake discharge

Abstract The transport of subglacial water beneath the East Antarctic Ice Sheet is an enigmatic and difficult to observe process which may affect the flow of the overlying ice and mixing of the oceans in the sub ice shelf cavities, and ultimately global climate. Periodic outbursts are a critical mechanism in this process. Recent analysis of satellite data has inferred a subglacial hydraulic discharge totaling 2 km 3 traveling some 260 km along the ice-bed interface of the Adventure Subglacial Trench between 1996 and 1998 (Wingham et al., 2006. Rapid discharge connects Antarctic subglacial lakes. Nature 440, 1033–1036). Using radar echo sounding data from the Adventure Subglacial Trench region in conjunction with the previously reported satellite observations, along with some basic modeling, we calculate a mass budget and infer a flow mechanism for the 1996–1998 event. The volume released from the source lake exceeded the volume received by the destination lakes by ~ 1.1 km 3 . This discrepancy indicates that some water must have escaped downstream from the lowest destination lake from 1997 onward. The downstream release of water from the destination lakes continued until at least 2003, several years after the 1998 cessation of surface subsidence at the source lake. By 2003 a total of 1.5 km 3 or nearly 75% of the water released by the source lake had traveled downstream from the destination lakes. The temporal evolution of discharge from the outlet can be simulated with the classic ice-walled semicircular channel model, if and only if the retreat of the source lake shoreline is taken into account. Further downstream, the ice bedrock geometry along the inferred flow path downstream includes many sections where thermal erosion of the overlying ice would not be sustainable. Along these reaches mechanical lifting of the ice roof and/or erosion of a sedimentary substrate by a broad shallow water system would be most effective means of sustaining the discharge. A distributed system is also consistent with the 3-month delay between water release at the source lake and water arrival at the destination lake. Observations of intermittent flat bright bed reflections in radar data acquired along the flow path are consistent with the presence of a broad shallow water system. Ultimately the presence of large subglacial lakes along the flow path of the 1996–1998 Adventure Subglacial Trench flow path delayed the arrival of water to points downstream by approximately 12 months.

Lateral epitaxial overgrowth of (0001) AlN on patterned sapphire using hydride vapor phase epitaxy

Coalesced, crack-free (0001) AlN films were grown on stripe patterned sapphire substrates without AlN seed layers using hydride vapor phase epitaxy. Using templates with stripes oriented in the ⟨112¯0⟩sapphire direction, lateral epitaxial overgrowth AlN films were coalesced over trench regions as wide as 10 μm despite parasitic sidewall and trench growth. Using transmission electron microscopy, a reduction in the dislocation density from 1.6×109 cm−2 in the seed region to less than 1.0×108 cm−2 in the wing region was demonstrated. Atomic force microscopy and cathodoluminescence measurements were also performed to assess the material quality.

Characteristics of GaN‐based light emitting diode grown on circular convex patterned sapphire substrate

AbstractWe report the characteristics of GaN‐based light‐emitting diode (LED) grown on a circular convex patterned sapphire substrate (CCPSS) and conventional LEDs on a non‐patterned sapphire substrate (PSS) by metal‐organic chemical vapor deposition. A near field scanning optical microscope (NSOM) and micro Raman spectroscopy were employed to investigate the crystalline properties. In NSOM image and spectra of LED on CCPSS, an improved crystalline quality with emission fluctuation feature on the trench region was obtained. However, stress relaxation in this trench region was not achieved due to the presence of voids, indicating a stress concentration at the coalescence region. Compared to conventional LED on non‐PSS, increased internal quantum efficiency (IQE) (41.8%) and reduced leakage currents (40 nA at ‐10 V) were observed in the LED fabricated on CCPSS. The light output power of the LED on CCPSS was approximately two times higher than that of a conventional LED. This enhancement of output power is contributed to increase of IQE and the effective suppression of leakage current by reduction of dislocation density, as well as enhanced light scattering via the circular convex facets. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical analysis of rapid water transfer beneath Antarctica

AbstractWe use a simple energy-conservation model and a model based on Röthlisberger’s theory for steady-state water flow in a subglacial conduit to model water movement between lakes in the Adventure subglacial trench region of East Antarctica during a 1996–98 jökulhlaup. Using available field evidence to constrain the models suggests that water flow would likely be accommodated in a tunnel with a cross-sectional area of 36 m2 and a value for k (the reciprocal of Manning’s roughness parameter) larger than the 12.5 m1/3 s−1 previously calculated. We also use Nye’s theory for time-dependent conduit water flow to model the temporal evolution of conduit discharge, cross-sectional area, water pressure and lake draining and filling during the flood. We initially assume one source and one sink lake. We perform sensitivity tests on the input parameter set, matching modeled source- and sink-lake depth changes with measured surface elevation data. Using a simple function for vertical ice deformation in which surface deformation scales linearly to the lake depth change, we find the scaling factor is of the order 4 × 10−3 of the ice thickness. The most likely value of k lies in the range 55–68 m1/3 s−1, and the ratio of source to sink-lake radii is approximately 1 : 1.4. Finally, we experiment using Nye’s theory to model water movement between one source and three sink lakes. The model fails to produce the observed patterns of water movement as indicated by the surface deformation data.

Growth behaviors of GaN/Si heteroepitaxy with various terrace widths grown by the LEPS method

Epilayers of GaN were grown on patterned Si (111) substrates of various terrace widths by means of metal organic chemical vapor deposition. The technique of lateral epitaxy on a patterned substrate used the growth of GaN epilayers from the periodic and parallel stripes that form as a result of the substrate etching. Silicon substrates were patterned for various terrace widths of 3 μm, 8 μm, and 18 μm. A low temperature AlN was used as a seed layer for the growth of a 1.5 μm thick GaN epilayer. The as-grown samples were characterized by using double-crystal X-ray diffractometry (DCXRD), photoluminescence and atomic force microscopy (AFM). From the DCXRD spectra, the full width at half maximum (FWHM) of the samples was found to decrease as the terrace width decreased. This behavior indicates that there is an improvement in the crystalline quality of the GaN epilayers as the terrace width decreases. The photoluminescence spectra reveal a decrease in the FWHM and an increase in the peak intensity as the terrace width decreases. This behavior indicates that there is an improvement in the optical quality of the GaN epilayer as the terrace width decreases. The atomic force micrographs reveal a dislocation-free homogeneous surface in the trench region compared to the terrace region with defects such as pits and dislocations. The results clearly show that GaN epilayers grown on a patterned Si substrate with a terrace width 3 μm have a good crystalline quality with minimal threading dislocation and excellent band edge emission.

Growth Mechanism and 2D Aluminum Dopant Distribution of Embedded Trench 4H-SiC Region

The migration enhanced embedded epitaxy (ME3) mechanism and 2D dopant distribution of the embedded trench region is investigated with the aim to realize the all-epitaxial, normally-off junction field effect transistor (JFET). We found that the embedded growth consists of two main components. First one is the direct supply without gas scattering and the other one is the surface migration supply via the trench opening edge, which dominate the ME3 process. An inhomogeneous 2D distribution of Aluminum (Al) concentration was revealed for the first time in the 4H-SiC embedded trench regions by the combined analysis of secondary ion mass spectrometry (SIMS) and scanning spreading resistance microscopy (SSRM) results. The maximum variation of Al concentration in the trench is estimated to be about 4-times, which suggests that the Al concentration is highest for the (0001) plane and lowest for the trench corner (1-10x) plane. Al concentration in the (1-100) plane, which determines the JFET p-gate doping level is 1.5-times lower than (0001) plane for trench region fabricated on Si-face wafers.

西南日本弧海溝寄り地域に分布する，中新世玄武岩質岩の微量元素・ Sr-Nd-Pb同位体組成

西南日本弧海溝寄り地域に分布する，中新世玄武岩質岩の微量元素・ Sr-Nd-Pb同位体組成

Facet formation and lateral overgrowth of selective Ge epitaxy on SiO2-patterned Si(001) substrates

Faceting and lateral overgrowth have been investigated for Ge selectively grown on Si(001) substrates in trench regions bound by SiO2 sidewalls. In wet-etched large trenches with sloped sidewalls, Ge faceting behavior was similar to Si and SixGe1−x faceting: slow-growing {113} facets dominate, with {111} facets expanding as the layer became thicker. However, the {111} facet length for Ge was much smaller than that of Si; this can be explained in terms of mass transport and accumulation, as well as energy minimization and the higher surface diffusivity of Ge. In dry-etched small trenches with vertical sidewalls, minimization of the high-energy interface area between Ge and SiO2 appears to be most critical in determining faceting morphology. Overgrowth of Ge led to void formation at the oxide interface, presumably to avoid the high-energy Ge/SiO2 interface. Upon coalescence of lateral-growth regions, fast-growing (001) forms and dominates subsequent growth. Thus, the total thickness of the overgrown Ge layer was closely related to the width of the SiO2 region between trenches.

P02 西南日本外帯の海溝寄り地域の中新世玄武岩質岩の地球化学的特徴(ポスターセッション,日本火山学会2007年秋季大会)

P02 西南日本外帯の海溝寄り地域の中新世玄武岩質岩の地球化学的特徴(ポスターセッション,日本火山学会2007年秋季大会)

Growth and Evaluation of GaN Grown on Patterned Sapphire Substrates

We report the microstructure and optical properties of gallium nitride (GaN) epilayers grown on lens shape patterned sapphire substrate (PSS) using metalorganic chemical vapor deposition (MOCVD) for various growth times. A lens shaped pattern was used to reduce the threading dislocation density and to improve optical emission efficiency. A scanning electron microscope (SEM) image shows flat and smooth surface of GaN grown on PSS at 80 min which could be achieved by lateral growth from the trench region. From the DCXRD spectra, full width at half maximun (FWHM) value was decreased with increasing growth time. FWHM of the sample grown at 80 min was 473.5 arc sec. This indicates there is an improvement in crystalline quality of the GaN grown on PSS as the growth time increases. From photoluminescence (PL) spectra, an increase in band edge emission intensity and a decrease in defect related yellow luminescence was observed for GaN on PSS as the growth time increased. From the PL spectra, FWHM was 82.2 meV at peak position 363.9 nm for the sample grown for 80 min. It is clearly seen that the threading dislocations can be reduced by lateral growth improving the light emission efficiency by internal light reflection on the lens surface for GaN grown on PSS.

Gravity constraints on the dynamics of the crust-mantle system during Calabrian subduction

SUMMARY The thermomechanic evolution of the lithosphere–upper mantle system during Calabrian subduction is analysed using a 2-D finite element approach, in which the lithosphere is compositionally stratified into crust and mantle. Gravity and topography predictions are cross-checked with observed gravity and topography patterns of the Calabrian region. Modelling results indicate that the gravity pattern in the arc-trench region is shaped by the sinking of light material, belonging to both the overriding and subduction plates. The sinking of light crustal material, up to depths of the order of 100–150 km is the ultimate responsible for the peculiar gravity signature of subduction, characterized by a minimum of gravity anomaly located at the trench, bounded by two highs located on the overriding and subducting plates, with a variation in magnitude of the order of 200 mGal along a wavelength of 200 km, in agreement with the isostatically compensated component of gravity anomaly observed along a transect crossing the Calabrian Arc, from the Tyrrhenian to the Ionian Seas. The striking agreement between the geodetic retrieved profiles and the modelled ones in the trench region confirms the crucial role of compositional stratification of the lithosphere in the subduction process and the correctness of the kinematic hypotheses considered in our modelling, that the present-day configuration of crust–mantle system below the Calabrian arc results from trench's retreat at a rate of about 3 cm yr−1, followed by gravitational sinking of the subducted slab in the last 5 Myr.

Formation of nanometer-scale structures in SiO2 thin films by means of MeV-ion irradiation

Future nanometer-scale electronic applications will require the engineering and modification of new materials on the atomic and molecular scale. In this article, we explore the possibility of using MeV heavy-ion irradiation to induce physical modifications on the materials of choice of the existing microelectronic technology, such as SiO2, metals and silicon, to form nanometer-scale structures. Micrometer-sized trenches or H-shaped structures were machined using focused ion-beam milling in Al/SiO2 and Au/SiO2 bilayers on crystalline Si. These samples were irradiated with a 4.6 MeV O2+ beam at room temperature, and the structures were studied by scanning electron microscopy. The micrometer-scale SiO2 structures underwent an anisotropic deformation induced by the electronic energy loss of the MeV incoming ions, leading to a major flow of SiO2 which fills the trench region. The target dimensions perpendicular to the beam direction increased, and the trench width or the micrometer-sized gaps of these structures decreased down to the nanometer scale as a function of the ion fluence. In the case of Al/SiO2 and Au/SiO2 bilayers, only the SiO2 film underwent the plastic deformation, and there is no flow of either the silicon substrate or the metallic layer.

Are asperity patterns persistent? Implication from large earthquakes in Papua New Guinea

We studied the distribution of asperities for large recent earthquakes along the New Britain trench, Papua New Guinea, to investigate if they are the same for repeated ruptures of the subduction boundary. We determined the slip distributions of two earthquakes (Mw ∼ 8) in 1971 using Pdiff waveforms, and an earthquake (Mw 7.9) in 1995 using direct teleseismic P waves. Combining these findings with previous results for two earthquakes (Mw ∼ 7.5) in 2000, we compared the source areas and asperity distributions for this region of the New Britain Trench. Our results show that the locations of the asperities for the individual earthquakes did not significantly overlap, although the same portion of the subduction zone seems to have reruptured. This fact supports the idea that asperities are not persistent features when portions of the New Britain subduction zone slip in large earthquakes.

Comment on “Tidal synchronicity of the 26 December 2004 Sumatran earthquake and its aftershocks” by R. G. M. Crockett et al.

[1] Crockett et al. [2006] report a striking coincidence of some of the larger recent earthquakes around the Sunda/ Andaman/Java trench regions with the times of the full and new moon. However, it may be worth noting that the results contradict nearly all previous studies and theoretical expectations, and the statistics invoked have some problems. [2] Two flavors of earthquake-tide correlations have been sought, with either the diurnal stress variations or the biweekly modulations in the amplitude of the stress envelope. A correlation with both tidal periods has occasionally been noted in the case of seismicity just below the ocean floor at mid-ocean ridges, but in each reported case the correlation with biweekly tides was much weaker than the correlation with diurnal tides [Wilcock, 2001; Tolstoy et al., 2002]. Extensive data on global tectonic earthquakes have sometimes shown evidence of a correlation with diurnal tides [Tanaka et al., 2002, Tsuruoka et al., 1995], especially in the case of the strongest tides [Cochran et al., 2004]. However, none of the studies report seeing a correlation with the biweekly tide. Even regional studies of far larger sets of earthquakes in the San Francisco Bay Area [McNutt and Heaton, 1981; Kennedy et al., 2004] and the Pacific Northwest [Kennedy et al., 2004] find no measurable correlation. As stated by Hartzell and Heaton [1989], the difference in the amplitude of the biweekly tidal stress envelope is much smaller than the diurnal peak-to-peak stress variation, with diurnal stress variation being over 5 times larger than the biweekly variation. Along the same vein, theoretical studies predict a correlation with the diurnal but not biweekly tides due to the small overall amplitude variation of biweekly tides [Dieterich, 1987]. [3] Crockett et al. [2006] base their conclusions on a comparison with the lunar phase only; however, it has been well documented, for example in a review by Emter [1997], that the tidal time series must be computed in relation to the focal mechanism to derive a useful correlation. In addition, Crockett et al. [2006] do not include the ocean tide component of the tidal stress in their correlation even though the ocean tide component is often an order of magnitude larger than the solid earth tide in subduction zone (coastal) environments. Depth matters as well; for example, Tsuruoka et al. [1995] show that tides calculated at the surface can be opposite in phase to tidal time series at hypocentral depths when ocean loading is taken into account. [4] Perhaps most importantly, the statistics employed by Crockett et al. [2006] are somewhat problematic. Schuster’s test is only valid for independent datasets in which events occur at random. This test can produce a false positive result if the data set is not random and so should not be used for statistical tests on catalogs that include aftershocks. Therefore, the statistics given by Crockett et al. [2006] for the raw (clustered) catalog are invalid. Specifically, in the clustered catalog, the times of aftershocks of the M9.3 megathrust dominate the sample, and they are not uncorrelated in time. Rather they tend to occur just after the mainshock, as aftershocks are prone to do. [5] The most compelling statistic of Crockett et al. [2006] is the one derived from 13/14 declustered events happening near the quadrants of either the full or new moons. An only 1-in-a-100 chance of finding the result at random is cited, but the paper documentation suggests the degrees of free-