Lateral Propagation Research Articles

Rift migration and lateral propagation: evolution of normal faults and sediment-routing systems of the western Corinth rift (Greece)

Abstract The active Corinth rift records hanging-wall migration of faulting and slip-rate acceleration. The rift initiated at approximately 5–4 Ma, and older parts are well exposed in the northern Peloponnese. A new correlation of chrono- and lithostratigraphy and structure across the onland central to westernmost rift with offshore data reveals westward rift propagation, as well as northward fault migration. Northward fault migration ended first in the east, with the stabilization of major north-dipping faults that now bound the Gulf. The basin then propagated to the WNW in two stages, each involving the initiation of a new fault that propagated east to SE to link to the stable fault system. Extension rates accelerated in distinct steps as the rift opened to the west. The youngest faults in the westernmost rift are associated with high seismicity and highest geodetic extension due to rapid fault growth and linkage at depth. The early synrift succession infilled substantial inherited palaeo-relief. Antecedent rivers established vigorous sediment-routing systems that controlled facies distribution throughout rifting, albeit with drainage reorganization during fault-migration events. Multiple deepening events recorded in the stratigraphy can be due to lateral rift propagation. The transition from rift initiation to rift climax is, therefore, diachronous along the rift axis.

Lateral Spreading Mechanism of a Turbulent Spot and a Turbulent Wedge

We examine the spreading of turbulent spots and wedges into a surrounding laminar Blasius boundary layer. The spreading is not due to the lateral propagation of turbulent eddies but rather to a developing disturbance in the surrounding spanwise vorticity of the laminar boundary layer. We concentrate on the mechanisms for generating streamwise vorticity. In particular, inclined generally streamwise vortex tubes along the spot/wedge boundary tilt mean shear vortex lines either up or down. These lines subsequently tend to either lag back or lead forward. As the leading or lagging vortex lines continue to wrap around and reinforce the causative inclined tube, the lines arch up or down. The outboard portion of the resulting arch must acquire a vertical, ωy, component of vorticity which induces the rollup of a new inclined tube now outboard of the first. Close to the wall the arching mechanism is inhibited by the no through flow boundary condition while far from the wall the process is inhibited by the lack of sufficient mean spanwise vorticity.

Provenance evolution during progressive rifting and hyperextension using bedrock and detrital zircon U-Pb geochronology, Mauléon Basin, western Pyrenees

The responses of sedimentary systems to rifting at continental margins are three-dimensional and involve the mixing of various sediment sources through tectonic drivers and sediment response. Such sedimentary responses have not been well studied along magma-poor, hyperextended margins where the crust is stretched and thinned to ≤10 km. The asymmetric Mauleon Basin of the western Pyrenees is the product of such magma-poor hyperextension resulting from lateral rift propagation from the Bay of Biscay during Cretaceous time. After rifting, limited shortening during Cenozoic Pyrenean inversion uplifted the basin, resulting in preservation of outcrops of rift basin fill, upper and lower crustal sections, serpentinized lithospheric mantle, and basic rift-fault relationships. In this study ~5800 new zircon U-Pb ages were obtained from prerift, synrift, and postrift strata; the ages constrain the proximal to distal evolution of the Mauleon Basin and define a general model for sediment routing during rifting. Zircon U-Pb analyses from lower crustal granulites indicate that granulite plutons crystallized at 279 ± 2 and 274 ± 2 Ma, and paragneissic granulites yielded zircon rim ages of ca. 295 Ma. Detrital zircon U-Pb ages from western Pyrenean prerift strata show age modes of ca. 615 and ca. 1000 Ma, suggesting continual recycling and/or well-mixed Gondwanan-sourced sediments throughout the Paleozoic and early Mesozoic; additional Paleozoic age components (ca. 300 and ca. 480 Ma) are also observed. The variation of detrital zircon U-Pb ages in synrift and postrift strata illustrates that during rifting, provenance varied spatially and temporally, and sediment routing switched from being regionally, to locally, and then back to regionally derived within individual structurally controlled subbasins.

Comparison of the dynamical response of low latitude middle atmosphere to the major stratospheric warming events in the Northern and Southern Hemispheres

This study presents comparison of low-latitude dynamical responses to boreal 2008/09 and austral 2002 winter Major Stratospheric Warming (MSW) events, as both events are of vortex split type. During these winters, planetary wave (PW) variability and changes in low-latitude circulation are examined using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis (ERA)-interim data sets and mesospheric wind data acquired by the MF radars at Tirunelveli (8.7°N) and Rarotonga (22°S). Eliassen-Palm diagnostic is used to provide an evidence for the lateral PW energy propagation from high to low-latitudes during both the MSW events. The PW flux reaches much lower latitudes during the boreal event than during the austral event. The low-latitude westward winds at stratospheric heights are stronger (weaker) during the boreal (austral) MSW. Weak (strong) PW wave activity at low latitude mesospheric heights during boreal (austral) MSW indicates the influence of low-latitude stratospheric westward winds on the vertical propagation of PW to low-latitude mesosphere.

Upslope Internal-Wave Stokes Drift, and Compensating Downslope Eulerian Mean Currents, Observed above a Lakebed

AbstractIn a small lake, where flows were dominated by internal waves with 10–32-h period, slow but persistent mean transport of water over many wave periods was examined. Acoustic Doppler profilers (ADPs) and a vertical string of temperature loggers were deployed where the lower thermocline intersected the sloping lakebed. Near (<1 m above) the bed, internal waves, coherent with a lakewide seiche, propagated upslope at ~0.023 m s−1. Near-bed wave-induced water velocity fluctuations had a standard deviation of <0.02 m s−1. Near the surface, velocity fluctuations had similar magnitude, but lateral wave propagation was unclear. Averaged over many wave periods, the near-bed Eulerian velocity flowed downslope at ~0.01 m s−1, and was roughly cancelled by an upslope internal-wave Stokes drift (estimated by assuming that weakly nonlinear waves propagated without change of form). To examine net transport, while relaxing approximations used to estimate the Stokes drift, the observed temperature range (9°–25°C) was divided into 0.5°C increments, and the depth-integrated, wave-averaged flux of water in each temperature class was calculated. The coldest (near-bed) water was slowly transported onshore, opposite the Eulerian mean velocity. Onshore flux of warm near-surface water was comparable to an Eulerian-mean flux, indicating minimal near-surface Stokes drift. Intermediate water, from the middle of the water column and the outer boundary layer, was transported offshore by an offshore Stokes drift. The downslope near-bed Eulerian mean velocity, together with intensification of mean stratification within 0.4 m of the bed, may enhance boundary layer mixing.

Dyke emplacement in the Narmada rift zone and implications for the evolution of the Deccan Traps

Abstract The Deccan Large Igneous Province of India is the product of fissure eruptions, and contains vast lava fields and dyke–sill networks. It is associated with several rift zones in peninsular India, which reflect pre-existing major weaknesses in the Indian lithosphere. In rift-zone eruptions, magma is normally transported to the surface through dykes. However, some injected dykes do not reach the surface but are arrested at depth in the rift zone due to mechanical heterogeneity and anisotropy, or insufficient magma pressure. In the present work, the effects of mechanical layering and regional tension on dyke emplacement in the Narmada rift zone are studied. The results indicate that the distribution of maximum principal tensile stresses was altered by mechanical layering and/or regional tension, which has led to variations in potential dyke propagation pathways. Studies on dyke evolution and emplacement in the Narmada rift zone indicate four evolutionary stages: stage I – arrival of a mantle plume and pre-volcanic extension; stage II – formation of shallow magma chambers; stage III – vertical dyke injection and fissure eruption; and stage IV – the ‘blanket effect’ and lateral dyke propagation.

Characterization of Flashing Phenomena with Cryogenic Fluid Under Vacuum Conditions

Flashing occurs when liquid undergoes a sudden depressurization and triggers a violent atomization and vaporization. This phenomenon may happen at the transient startup of the upper-stage rocket engine. In this paper, experimental investigation of cryogenic fluid injection into a low-pressure environment is performed using liquid nitrogen instead of the real cryogenic propellants (liquid oxygen and liquid methane). With the help of a high-speed shadowgraph technique and with the temperature measurement, the characteristics of flashing are explored, including its evolution process, the spray angle, the spray thermal behaviors along the injection centerline, and the spray phase solidification. The results show that bubble nucleation is a reasonable controlling factor for the flashing evolution process. The nondimensional energy barrier is conditionally indicative of the flashing transition process, and it works well under low injection temperature conditions. The drastic temperature drop due to flashing phenomena causes liquid jet solidification, which may pose a challenge for the engine startup process. An analysis of the spray lateral propagation indicates that superheat exerts a substantial effect on the spray angle enhancement; however, this enhanced effect is found to decrease with an increase of liquid superheat.

Evidence of complex site effects and soil non-linearity numerically estimated by 2D vs 1D seismic response analyses in the city of Xanthi

This study discusses the effects of local site conditions on earthquake ground motion for city of Xanthi, North-Eastern Greece, focusing on the influence of complex site effects and soil non-linearity. Although city of Xanthi is characterized as a low seismicity area, documented strong earthquake events of past centuries indicate the necessity of an appropriate estimation of ground surface motion of the region. Therefore, a typical 2D cross-section along the city following an E-W direction is constructed, based on the synthesis of available geological, geotechnical and geophysical data of the broader area. 1D and 2D numerical models are generated utilizing the Finite Difference Method and site response is investigated for different seismic scenarios. Wave amplification is captured as a result of 1D resonance phenomena integrated with potential 2D complex wave effects, due to lateral propagation of the locally generated at the discontinuities surface waves. The additional, relatively to 1D, 2D amplification or de-amplification of ground shaking, in terms of its amplitude and its spectral content is quantified. The impact of soil deposits non-linearity on amplification level, as well as, on generated 2D wave fields is considered by implementing both equivalent-linear and non-linear approaches. The results reveal that, across the city, spatial variation of ground surface motion is obvious, attributed primarily to the variation of subsurface soil profiles. 2D wave effects have been generated signifying that, at particular site locations, ground motion is additionally amplified or de-amplified with respect to 1D response. However, 2D versus 1D differentiation has been calculated of ±20% in terms of PGA and spectral accelerations up to 1.0s, in the majority of the examined sites, implying that site response even though, influenced by 2D resonance phenomena, could be sufficiently captured by an 1D approach. Moreover, it is shown that if soil non-linearity is properly accounted for, it may play an important role on the estimated ground response, since non-linear approach seems to produce lower amplification levels with regard to 1D and 2D equivalent-linear approaches. As a general trend across the investigated site, for the entity of the various scenarios, the numerically calculated response spectra exceed EC8 seismic code provisions.

Deep fluid transfer evidenced by surface deformation during the 2014–2015 unrest at Piton de la Fournaise volcano

Identifying the onset of volcano unrest and providing an unequivocal identification of volcano reawakening remain challenging problems in volcanology. At Piton de la Fournaise, renewal of eruptive activity in 2014–2015, after 41months of quiescence and deflation, was associated with long-term continuous edifice inflation measured by GNSS. Inflation started on June 9, 2014, and its rate progressively increased through 2015. Inflation onset was rapidly followed by an eruption on June 20–21, 2014, showing that volcano reactivation can be extremely fast, even after long non-eruptive phases. This short-lived eruption involved a shallow source (1.3–1.9km depth below the summit). The inflation that followed, and eruptions in 2015, involved a larger depth range of fluid accumulation, constrained by inverse modeling at ca. 3.9 to 1.2–1.7km depth. This time evolution reveals that volcano reawakening was associated with continuous pressurization of the shallowest parts of its plumbing system, triggered by progressive upwards transfer of magma from greater depth. A deep magma pulse occurred in mid-April 2015 and was associated with deep seismicity (3 to 9.5km depth) and CO2 enrichment in fluids emitted by summit fumaroles. From this date, ground deformation accelerated and the output rates of eruptions increased, culminating in the long-lasting, large-volume, August–October eruption (~36Mm3). This evolution suggests that deep magma/fluid transfer through an open conduit system first provoked the expulsion of the top of the plumbing system in June 2014, and then induced the progressive vertical transfer of the entire plumbing system down to 9km (four eruptions in 2015). The new sustained feeding of the volcano was also at the origin of the hydrothermal system perturbation and the acceleration of the eastern flank motion, which favor lateral dike propagation and the occurrence of frequent and increasingly large eruptions. Our results highlight the fast and progressive way in which basaltic magmatic systems can wake up.

Fabrication of suspended light-emitting diode and waveguide on a single chip

We attempt to integrate light-emitting diode (LED) and waveguide on the same GaN-on-silicon platform, which is fashioned with suspended p–n junction InGaN/GaN multiple quantum wells. Silicon substrate is removed to form highly confined waveguide structures and suspended LED. The light emission measurements experimentally demonstrate that part of the LED emission is coupled into suspended waveguide. The light is then guided in the waveguide and propagates along the waveguide structure, and is finally diffracted into the air at the waveguide output facet. The light spectra captured by a micro-transmittance setup confirm that the lateral light propagation inside the waveguide is electrically driven and power-dependent. These results indicate that the proposed integrated device is promising for the monolithic integration of LED with waveguide and photodetector toward next-generation photonic chips based on the GaN-on-silicon platform.

Tectonic evolution of the North Patagonian Andes (41°–44° S) through recognition of syntectonic strata

The North Patagonian fold-thrust belt (41°–44° S) is characterized by a low topography, reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone. This particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment. Here, new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages, evaluating the prevailing crustal regime for the different mountain domains through time. Growth strata and progressive unconformities, controlled by extensional or compressive structures, were recognized in volcanic and sedimentary rocks from the cordilleran to the extra-Andean domain. These data were used to construct a balanced cross section, whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology. Our results indicate two main compressive stages, interrupted by an extensional relaxation period. The first contractional stage in the mid-Cretaceous inverted Jurassic–Lower Cretaceous half graben systems, reactivating the western Cañadón Asfalto rift border ~500km away from the trench, at a time of arc foreland expansion. For this stage, available thermochronological data reveal forearc cooling episodes, and global tectonic reconstructions indicate mid-ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement. Widespread synextensional volcanism is recognized throughout the Paleogene during plate reorganization; retroarc Paleocene-–Eocene flare up activity is interpreted as product of a slab rollback, and fore-to-retroarc Oligocene slab/asthenospheric derived products as an expression of enhanced extension. The second stage of mountain growth occurred in Miocene time associated with Nazca Plate subduction, reaching nearly the same amplitude than the first compressive stage. Extensional weakening of the upper plate predating the described contractional stages appears as a necessary condition for abnormal lateral propagation of deformation.

Anatomy and paleofluid evolution of laterally restricted extensional fault zones in the Jabal Qusaybah anticline, Salakh arch, Oman

The E-W−trending Jabal Qusaybah anticline, at the western termination of the Salakh arch, Oman Mountains, is characterized by a complex fault network that developed in layered Cretaceous carbonates. This network includes NE-SW left-lateral, N-S extensional, and subordinate E-W extensional fault zones. The N-S−striking extensional faults zones are roughly perpendicular to the fold axis and are best developed in the longitudinally bulged central sector of the anticlinal crest. They are likely due to along-strike outer-arc extension associated with positive fault inversion and salt migration. These extensional fault zones are confined within, and locally abut, major NE-SW left-lateral strike-slip fault zones. Extensional fault displacements range between a few decimeters and ∼60 m, whereas the maximum exposed trace lengths range between a few meters and ∼800 m. Narrow (∼1−15-cm-thick) cataclastic fault cores are surrounded by vein-dominated damage zones as thick as tens of meters. Moreover, fault zones show widespread evidence for substantial dilation in the form of (1) dilation breccias, (2) infilling by large columnar calcite crystals and aggregates, and (3) centimeter- to meter-thick veins. Dilation breccias and calcite infillings are primarily localized at fault tips, fault overlaps, and interaction zones between strike-slip and extensional fault segments. Displacement profiles along the N-S−striking extensional fault zones indicate that they are one order of magnitude shorter than values predicted by most published displacement-length scaling laws. By analyzing fault abutting geometries, detailed vein relative chronology, δ13C and δ18O signatures, and fluid inclusion data from calcite veins and calcite fault infillings, we propose a model whereby a deep-seated, regionally sized, left-lateral strike-slip fault system that was active during anticline growth inhibited the lateral propagation of late-stage transversal extensional fault zones. Our findings show that, in this geological setting, the structural position, rather than fault displacement, is the parameter controlling the location of the more dilatants (and permeable) fault segments. Results of the present work suggest that fault intersections may be more useful than fault throw for predicting zones of enhanced vertical fluid flow in structurally complex carbonate reservoirs.

Optical crosstalk analysis of micro‐pixelated GaN‐based light‐emitting diodes on sapphire and Si substrates

With the aid of depth‐resolved confocal microscopy, the optical crosstalk phenomenon in GaN‐based micro‐pixel light‐emitting diodes (μ‐LEDs) on Si substrates are thoroughly investigated and compared with its counterpart on sapphire substrate. Noticeable optical crosstalk is invariably present in GaN‐on‐sapphire devices as the thick transparent sapphires beneath the μ‐LEDs serve as optical waveguides to favor lateral propagation of the emitted light, eventually causing unwanted noise signals. μ‐LEDs adopting the GaN‐on‐Si platform can effectively suppress unwanted optical crosstalk and sustain superior performance at different injection currents, which are well‐suited for a wide range of μ‐LED applications.Light intensity maps illustrating crosstalk performances of GaN‐on‐sapphire μ‐LEDs with backsides coated with (left) Al mirror and (middle) black paint, and (right) GaN‐on‐Si μ‐LED, captured by confocal microscopy.

Suspended GaN-based nanostructure for integrated optics

We show the fabrication and characterization of a suspended GaN-based nanostructure in the visible wavelength region that combines InGaN/GaN multiple quantum wells (MQWs) active layer with rib waveguides and then creates multiple separate beamlets. It is implemented on a GaN-on-silicon platform, where silicon substrate is removed and suspended epitaxial films are thinned by back wafer etching technique. When the InGaN/GaN MQWs active layer is optically excited, part of the emitted light is confined inside epitaxial films and acts the light source. The lateral propagation direction is controlled by the rib waveguide, and the light intensity and the propagation mode can be tuned by changing the rib waveguide structure. Experimental and simulated results indicate the proposed suspended GaN-based structure is promising for the integration of emitting device with planar optical circuit in the visible wavelength region.

A Hilbert Transform Based Shear Wave Speed Estimation Method for Shear Wave Elasticity Imaging

In this paper, a Hilbert transform based method is used to estimate shear wave speed. Shear wave speed can be measured from the lateral propagation of particle displacements or velocities within the tissue, these particle displacements or velocities are generated by simulating radio frequency signals measured from ultrasound probe elements that image the displaced particles generated from a finite-element model (FEM) that simulates the dynamic response of tissues to acoustic radiation forces. The proposed shear wave speed estimation method is based on locating a zero-amplitude crossing in the Hilbert transform of the cross-correlation function between the particle displacement measured at first lateral location greater than the lateral width of shear wave and the displacement measured and subsequent lateral lines under examination at a certain depth. The results obtained from this method is compared to the lateral Time to Peak (TTP) method that finds the instance at which the maximum displacement is detected at each lateral location under examination at a certain depth. The proposed algorithm reveals a reconstruction of materials having shear modulus of 1.43±0.20, 2.92±0.39, 4.09±0.54, 8.13±1.06, 12.11±1.52, 16.16±2.08 kPa on particle displacement signals for 1.33, 2.835, 4, 8, 12, and 16 kPa shear moduli materials respectively and 1.34±0.40, 2.66±0.41, 3.77±0.58, 7.45±1.14, 11.34±1.51, and 14.90±2.08 kPa on particle velocity signals for 1.33, 2.835, 4, 8, 12, and 16 kPa shear moduli materials respectively. Finally, the proposed method is based on locating a zero-amplitude crossing in the Hilbert transform of the cross-correlation function appears to provide more accurate results than Lateral TTP method.

Dislocation confinement in the growth of Na flux GaN on metalorganic chemical vapor deposition-GaN

We have demonstrated a GaN growth technique in the Na flux method to confine c-, (a+c)-, and a-type dislocations around the interface between a Na flux GaN crystal and a GaN layer grown by metalorganic chemical vapor deposition (MOCVD) on a (0001) sapphire substrate. Transmission electron microscopy (TEM) clearly revealed detailed interface structures and dislocation behaviors that reduced the density of vertically aligned dislocations threading to the Na flux GaN surface. Submicron-scale voids were formed at the interface above the dislocations with a c component in MOCVD-GaN, while no such voids were formed above the a-type dislocations. The penetration of the dislocations with a c component into Na flux GaN was, in most cases, effectively blocked by the presence of the voids. Although some dislocations with a c component in the MOCVD-GaN penetrated into the Na flux GaN, their propagation direction changed laterally through the voids. On the other hand, the a-type dislocations propagated laterally and collectively near the interface, when these dislocations in the MOCVD-GaN penetrated into the Na flux GaN. These results indicated that the dislocation propagation behavior was highly sensitive to the type of dislocation, but all types of dislocations were confined to within several micrometers region of the Na flux GaN from the interface. The cause of void formation, the role of voids in controlling the dislocation behavior, and the mechanism of lateral and collective dislocation propagation are discussed on the basis of TEM results.

Controls on transgressive sill growth

Igneous sills represent an important contribution to upper crustal magma transport and storage. This study focuses on an exemplary 20–50-m-thick transgressive sill in the Faroe Islands on the European Atlantic passive margin, which is hosted in layered lavas (1–20 m thick) and basaltic volcaniclastic units (1–30 m thick). Preserved steps in the sill, and offset intrusive segments, are consistent with initial propagation via segmented fractures followed by inflation to create a through-going sheet. Although steps correspond to the position of some host rock interfaces and volcaniclastic horizons, most interfaces are bypassed. Transgressive sill contacts are subparallel to thrust faults that record ENE-WSW shortening, which are observed within the surrounding country rock and within the sill. Remnant sill segments are elongate along a NNW-SSE axis, parallel to the derived intermediate stress axis for thrust faults. The overall transgressive geometry is consistent with regional horizontal shortening, with steps indicating transitions between transgressive and lateral sill propagation are controlled locally by layering. This work emphasizes the importance of scale of observation in considering the controls on sill emplacement, and in particular, that layering is not the primary control on geometry.

On the mechanisms governing dike arrest: Insight from the 2000 Miyakejima dike injection

Magma stored beneath volcanoes is sometimes transported out of the magma chambers by means of laterally propagating dikes, which can lead to fissure eruptions if they intersect the Earth's surface. The driving force for lateral dike propagation can be a lateral tectonic stress gradient, the stress gradient due to the topographic loads, the overpressure of the magma chamber, or a combination of those forces.The 2000 dike intrusion at Miyakejima volcano, Izu arc, Japan, propagated laterally for about 30 km and stopped in correspondence of a strike-slip system, sub-perpendicular to the dike plane. Then the dike continued to inflate, without further propagation. Abundant seismicity was produced, including five M>6 earthquakes, one of which occurred on the pre-existing fault system close to the tip of the dike, at approximately the time of arrest. It has been proposed that the main cause for the dike arrest was the fault-induced stress.Here we use a boundary element numerical approach to study the interplay between a propagating dike and a pre-stressed strike-slip fault and check the relative role played by dike–fault interaction and topographic loading in arresting the Miyakejima dike. We calibrate the model parameters according to previous estimates of dike opening and fault displacement based on crustal deformation observations. By computing the energy released during the propagation, our model indicates whether the dike will stop at a given location. We find that the stress gradient induced by the topography is needed for an opening distribution along the dike consistent with the observed seismicity, but it cannot explain its arrest at the prescribed location. On the other hand, the interaction of dike with the fault explains the arrest but not the opening distribution. The joint effect of the topographic load and the stress interaction with strike-slip fault is consistent with the observations, provided the pre-existing fault system is pre-loaded with a significant stress, released gradually during the dike–fault interplay.Our results reveal how the mechanical interaction between dikes and faults may affect the propagation of magmatic intrusions in general. This has implications for our understanding of the geometrical arrangement of rift segments and transform faults in Mid Ocean Ridges, and for the interplay between dikes and dike-induced graben systems.

Forecasting the path of a laterally propagating dike

AbstractAn important aspect of eruption forecasting is predicting the path of propagating dikes. We show how lateral dike propagation can be forecast using the minimum potential energy principle. We compare theory to observed propagation paths of dikes originating at the Bárðarbunga volcano, Iceland, in 2014 and 1996, by developing a probability distribution for the most likely propagation path. The observed propagation paths agree well with the model prediction. We find that topography is very important for the model, and our preferred forecasting model considers its influence on the potential energy change of the crust and magma. We tested the influence of topography by running the model assuming no topography and found that the path of the 2014 dike could not be hindcasted. The results suggest that lateral dike propagation is governed not only by deviatoric stresses but also by pressure gradients and gravitational potential energy. Furthermore, the model predicts the formation of curved dikes around cone‐shaped structures without the assumption of a local deviatoric stress field. We suggest that a likely eruption site for a laterally propagating dike is in topographic lows. The method presented here is simple and computationally feasible. Our results indicate that this kind of a model can be applied to mitigate volcanic hazards in regions where the tectonic setting promotes formation of laterally propagating vertical intrusive sheets.

Suspended p–n Junction InGaN/GaN Multiple-Quantum-Well Device With Selectable Functionality

We demonstrate optoelectronic devices implemented on suspended p–n junction InGaN/GaN multiple quantum wells (MQWs) for the further monolithic integration of an optical source, a waveguide, and a photodetector on the same GaN-on-silicon wafer. The fabricated suspended membrane device exhibits selectable functionalities either for efficient light-emitting diodes (LEDs) or sensitive photodetectors. Typical current–voltage (I-V) characteristics are obtained for the device operated under the LED mode, and the emitted light intensity is effectively modulated by the applied voltage. Lateral in-plane propagation of emitted light in a suspended membrane is experimentally presented. The simulation results show that the thickness-dependent optical performance can be tuned by back wafer thinning for epitaxial films. The device operated under the photodetector mode exhibits a static photocurrent on–off ratio $\eta_{s}$ of $2.25\times 10^{5}$ at a 1-V bias voltage with the illumination power of 690 $\mu\mbox{W}$ and the wavelength of 450 nm. The photocurrent also shows a rectangular pulse response of the same duration as a 1-s rectangular illumination pulse at a 0-V bias voltage with the illumination power of 1 mW. The temporal photocurrent on–off ratio $\eta_{t}$ is around $1.01\times 10^{5}$ . This paper opens a promising way to realize the monolithic integration of a LED, a waveguide, and a photodetector on a GaN-on-silicon platform.