Boundary Off Research Articles

Microphysics of shock-grain interaction for inertial confinement fusion ablators in a fluid approach.

Ablator materials used for inertial confinement fusion, such as high-density carbon (HDC) and beryllium, have grain structure which may lead to small-scale density nonuniformity and the generation of perturbations when the materials are shocked and compressed. Here, we use a combination of a linear theory of shock interaction with density nonuniformity [Velikovich et al., Phys. Plasmas 14, 072706 (2007)10.1063/1.2745809] and numerical simulations to study shock interaction with a model representation of HDC grains. While the shock-grain interaction is nonlinear, the linear theory shows some key features of the shock-grain interaction, which also hold for the (nonlinear) simulations. The postshock perturbations are made up of sonic reflections off of grain boundaries and vorticity deposition along them, with the latter dominating the perturbed energy content. The mean (per mass) postshock perturbed kinetic energy decreases with increasing grain size, but energy will be deposited at increasing spatial scale. From the perspective of the postshock perturbed energy, the detailed linear theory largely supports a proposed method [S. Davidovits et al., Phys. Plasmas 29, 112708 (2022)1070-664X10.1063/5.0107534] for deresolving the grains (in a similar grains model) that treats the grains statistically. Our simulation results highlight the influence of thermal conduction on the perturbation dynamics at grain scales.

Flow-topography interactions in the western tropical Atlantic boundary off Northeast Brazil

Flow-Topography Interaction can be considered as a particular set of processes resulting of the currents interaction with a topographic gradient, specially associated with submarine canyon areas, which are important morphological features with potential to upwelling and cross-isobath transport on the continental margins. The South Pernambuco Continental Shelf (SPCS) and Pernambuco Plateau located on the Southwestern Tropical Atlantic (SWTA), present incised morphological features, highlighting the shelf valleys and blind canyons, which do not have a connection to the shelf or an onshore river system. They are likely features for interactions between the dominant along-shelf flow represented by the strong western boundary North Brazil Undercurrent. We investigated potential canyon induced upwelling and the respective mechanisms at the late spring/early fall context. CTD and reanalysis data from GLORYS12V1, and in situ bathymetric measurements were used to characterise the hydrodynamics and canyon morphology, respectively. Then, we combined both to obtain dimensionless numbers from dynamical scale analysis to infer possible imbalances of the acting forces. Reanalysis data evidenced uplift at the slope not related to the blind canyons. CTD data indicated a seasonal variation of the intrusion of water masses, especially at the shelf-break for the Middle shelf valley and Campas shelf valley. A temperature difference of 2.5 °C (2.0 °C) between surface and deep waters was observed during the late spring. A stepwise temperature structure was present in both seasons, indicating instability below the mixed layer depth, the uplifting of isotherms, and the corrosion of the lower portion of the surface mixed layer. The dimensionless parameters analysis reveals highest Rossby values during the fall, mainly in Zieta shelf valley (R0=130.87) and Csv (R0=111.71), and lower values for the canyons of the Pernambuco Plateau. Our hypothesis is that the shelf valleys might play a role in conducting the uplifted slope water coast-ward. For the blind canyons, although no related upwelling was observed, reanalysis revealed the presence of a deep anti-cyclonic eddy at one of the blind canyon's mouth. Rossby and Burger numbers indicate a weak geostrophic balance at the canyon rim, and instability of the horizontal length scale of the pressure gradient force, with tendency to vorticity control. While the paradigm that shelf and coastal waters off north-eastern Brazil are mostly oligotrophic in the surface is true, our observation of shallow (<60 m) subsurface uplift should be considered in future works in the SWTA.

Large-scale evolution of the central-east Greenland margin: New insights to the North Atlantic glaciation history

Abstract The continental shelf of central-east Greenland is shaped by several glacially carved transverse troughs that form the oceanward extension of the major fjord systems. The evolution of these troughs through time, and their relation with the large-scale glaciation of the Northern Hemisphere, is poorly understood. In this study seismostratigraphic analyses have been carried out to determine the morphological and structural development of this important sector of the East Greenland glaciated margin. The age of major stratigraphic discontinuities has been constrained by a direct tie to ODP site 987 drilled in the Greenland Sea basin plain off Scoresby Sund fan system. The areal distribution and internal facies of the identified seismic units reveal the large-scale depositional pattern formed by ice-streams draining a major part of the central-east Greenland ice sheet. Initial sedimentation along the margin was, however, mainly controlled by tectonic processes related to the margin construction, continental uplift, and fluvial processes. From late Miocene to present, progradational and erosional patterns point to repeated glacial advances across the shelf. The evolution of depo-centres suggests that ice sheet advances over the continental shelf have occurred since late Miocene, about 2 Myr earlier than previously assumed. This cross-shelf glaciation is more pronounced during late Miocene and early Pliocene along Blosseville Kyst and around the Pliocene/Pleistocene boundary off Scoresby Sund; indicating a northward migration of the glacial advance. The two main periods of glaciation were separated by a major retreat of the ice sheet to an inland position during middle Pliocene. Mounded-wavy deposits interpreted as current-related deposits suggest the presence of changing along-slope current dynamics in concert with the development of the modern North Atlantic oceanographic pattern.

Holocene turbidites record earthquake supercycles at a slow-rate plate boundary

Ongoing evidence for earthquake clustering calls for records of numerous earthquake cycles to improve seismic hazard assessment, especially where recurrence times overstep historical records. We show that most turbidites emplaced at the Africa-Eurasia plate boundary off west Algeria over the past ∼8 k.y. correlate across sites fed by independent sedimentary sources, requiring a regional trigger. Correlation with paleoseismic data inland and ground motion predictions support that M ∼7 earthquakes have triggered the turbidites. The bimodal distribution of paleo-events supports the concepts of earthquake supercycles and rupture synchronization between nearby faults: 13 paleo-earthquakes underpin clusters of 3–6 events with recurrence intervals of ∼300–600 yr, separated by periods of quiescence of ∼1.6 k.y. without major events on other faults over the study area. This implies broad phases of strain loading alternating with phases of strain release. Our results suggest that fault slip rates are time dependent and call for revising conventional seismic hazard models

津波遡上高の詳細分布から推定される2011年東北地方太平洋沖地震の断層モデル

The distribution of tsunami run-up heights generally has spatial variations, because run-up heights are controlled by coastal topography including local-scale landforms such as natural levees, in addition to land use. Focusing on relationships among coastal topography, land conditions, and tsunami run-up heights of historical tsunamis—Meiji Sanriku (1896 A.D.), Syowa Sanriku (1933 A.D.), and Chilean Sanriku (1960 A.D.) tsunamis—along the Sanriku coast, it is found that the wavelength of a tsunami determines inundation areas as well as run-up heights. Small bays facing the Pacific Ocean are sensitive to short wavelength tsunamis, and large bays are sensitive to long wavelength tsunamis. The tsunami observed off Kamaishi during the 2011 off the Pacific coast of Tohoku Earthquake was composed of both short and long wavelength components. We examined run-up heights of the Tohoku tsunami, and found that: (1) coastal areas north of Kamaishi and south of Yamamoto were mainly attacked by short wavelength tsunamis; and (2) no evidence of short wavelength tsunamis was observed from Ofunato to the Oshika Peninsula. This observation coincides with the geomorphologically proposed source fault model, and indicates that the extraordinary large slip along the shallow part of the plate boundary off Sendai, proposed by seismological and geodesic analyses, is not needed to explain the run-up heights of the Tohoku tsunami. To better understand spatial variations of tsunami run-up heights, submarine crustal movements, and source faults, a detailed analysis is required of coastal topography, land conditions, and submarine tectonic landforms from the perspective of geomorphology.

Seismic and gravity constraints on the nature of the basement in the Africa‐Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin

AbstractWe present a new classification of geological domains at the Africa‐Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene‐to‐present‐day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high‐velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine‐Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike‐slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain.

Mixing process on the northeast coast of Hokkaido in summer

Direct measurements using a free-falling micro-profiler were conducted on the northeast coast of Hokkaido in the summer of 2007 to clarify the mixing process in the Soya Warm Current (SWC) region in terms of microstructure. The distribution of the Turner angle (Tu) showed that these regions have a high potential for double diffusive convection, but direct measurements of the turbulent dissipation rate (e) and dissipation of temperature variance (\( \chi_{T} \)) did not necessarily correspond to each other in the SWC region, especially in the offshore front of SWC and farther offshore. The mixing efficiency indicated that, even though the Turner angle (Tu) indicated a high potential for double diffusive convection, turbulent mixing was the main contributor to the mixing process in this region, and double-diffusive convection only contributed partially and sparsely, especially in the boundary off SWC water. The bottom mixed layer (BML) is known to thicken off the SWC. The vertical diffusivity coefficient was enhanced near the bottom (10−4–10−3 m2 s−1) off the SWC, and these results support that turbulence near the bottom off the SWC contributed to the thickening of the BML.

Seismic reflection and bathymetric evidences for the Nankai earthquake rupture across a stable segment-boundary

Seismic reflection profiles reveal steeply landward-dipping splay faults in segment B (the 1946 Nankai earthquake rupture, M 8.3) as well as segment C (the 1944 Tonankai earthquake rupture, M 8.1) of the Nankai subduction zone. The splay faults, branching upward from the plate-boundary interface, almost reach the seafloor, producing seafloor fault scarps. The swath-bathymetry map exhibits a ∼200-km-long, remarkable seafloor lineament with which the seafloor fault scarps align in the segments B and C. The seafloor lineament, which we believe is produced by repeating slips on the splay faults, is almost laterally continuous across a stable boundary off Kii Peninsula inbetween the two segments. These seafloor and subsurface features could be due to multiple, simultaneous coseismic slips across the B–C boundary, when subduction thrust earthquakes accompany the co-seismic slips on the splay fault. The splay faults are associated with (1) fluid expulsion, (2) dynamic deformation, and (3) tsunami generation.

Similarities and Differences in the Rupture Process of the M 4.8 Repeating-Earthquake Sequence off Kamaishi, Northeast Japan: Comparison between the 2001 and 2008 Events

Earthquakes of M ∼5 have repeatedly occurred at the same location on the plate boundary off Kamaishi, northeast Japan, with a mean recurrence interval of about 5.5 years. The latest two events ( M 4.8 on 13 November 2001, and M 4.7 on 11 January 2008) were successfully observed by the broadband seismic network of Tohoku University covering the Tohoku District of northeast Japan. We estimated the source processes of the 2001 and 2008 events by carefully picking the onsets of P and S waves and by inverting seismic waveforms recorded by the network. The results show that both events were caused by the rupture of the same asperity patch (diameter, ∼1 km). As the previous 1995 event was also reported to have ruptured the source area of the 2001 event, at least the last three events (1995, 2001, and 2008) in this earthquake sequence are thought to have been caused by repeated ruptures of the same asperity. A closer examination, however, reveals a small discrepancy in the slip distribution between the last two events, which explains the difference in the high-frequency components of the seismograms. The regions in which slip was smaller during the 2001 event than during the 2008 event nearly coincide with the source areas of the smaller repeating earthquakes that occurred just before the 2001 event. This finding suggests that the activity of smaller events immediately before the mainshock can influence the slip distribution of the mainshock.

Coseismic slip distribution of the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) estimated based on GPS data— Was the asperity in Miyagi-oki ruptured?

We investigated the crustal deformation associated with the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) that occurred on March 11, 2011, along the plate boundary off Tohoku district, northeastern Japan, based on dense GPS observation. Coseismic displacements due to this event were applied to estimate the causal interplate slip by means of a geodetic inversion analysis. The major slip area is located around the asperities of the 1981 Miyagi-oki (M 7.2) and 2003 Fukushima-oki (M 6.8) earthquakes and the maximum slip is estimated as being up to 35 m. The estimated slip distribution suggests that the asperities of the Miyagi-oki earthquake in 1978 (M 7.4) that had not been ruptured during the Miyagi-oki earthquake in 2005 were ruptured as a part of the main shock fault of the 2011 off the Pacific coast of Tohoku Earthquake.

Restoration of interplate locking after the 2005 Off-Miyagi Prefecture earthquake, detected by GPS/acoustic seafloor geodetic observation

[1] A 7.2-magnitude earthquake occurred on the plate boundary off Miyagi Prefecture, northeastern Japan, on 16 August 2005. From seafloor geodetic observations using the GPS/acoustic combination technique in this area, we have detected notable seafloor movements associated with, and subsequent to this event. The time series of horizontal coordinates obtained at the seafloor reference point MYGW, located about 10 km east of the epicenter, indicates that the strain accumulated for the interseismic period was partly released by the event and a constant strain accumulation restarted after 1–2 years of the post-seismic period with an erratic movement. The horizontal velocity of MYGW after the restart above is estimated to be about 5.7 cm/year toward WNW relative to the Eurasian plate. Our result is consistent with those derived from terrestrial GPS measurements and implies that the interplate locking was restored in the rupture area of the 2005 event around 2007.

Arc–continent collision and orogenesis in western Tasmanides: Insights from reactivated basement structures and formation of an ocean–continent transform boundary off western Tasmania

Crustal architecture in formerly contiguous basement terranes in SE Australia, Tasmania and northern Victoria Land is a legacy of late Neoproterozoic–Cambrian subduction-related processes, culminating in formation of the Delamerian–Ross orogen. Structures of Delamerian–Ross age were subsequently reactivated during late Mesozoic–Cenozoic Gondwana breakup, strongly influencing the geometry of continental rifting and providing clues about the origins and configuration of the pre-existing basement structures. An ocean–continent transform boundary developed off western Tasmania follows the trace of an older Paleozoic strike-slip structure (Avoca–Sorell fault system) optimally oriented for reactivation during the final separation of Australia from Antarctica. This boundary cuts across rocks preserving an earlier record of arc–continent collision during the course of which continental crust was subducted to mantle depths and Cambrian mafic–ultramafic island arc rocks were thrust westwards over late Neoproterozoic–Cambrian passive margin sequences. Collision was accompanied by development of a foreland basin into which 520–600 Ma arc-derived detrital zircons were shed. Following a reversal in subduction polarity, and change to transcurrent motion along the Gondwana margin, Tasmania migrated northward along the proto-Avoca fault system before entering a subduction zone located along the Heathcote–Governor fault system, precipitating a second collision, south-vergent thrusting, and tectonic reworking of the already accreted Cambrian arc–forearc assemblages and underlying passive margin sequences.

Basement architecture and formation of an ocean-continent transform boundary off western Tasmania: insights from aeromagnetic and seismic reflection data collected from a frontier petroleum province

Basement architecture and formation of an ocean-continent transform boundary off western Tasmania: insights from aeromagnetic and seismic reflection data collected from a frontier petroleum province

Plasticity effects in dynamically loaded nickel aluminide bicrystals

This work is concerned with achieving an improved understanding of the role of material strength effects during interactions of shock waves with grain boundaries. To this end, experiments have been performed using nanosecond laser shocks of nickel aluminide bicrystals at tens of GPa. Velocity histories were measured along a line on the free surface of the bicrystals and used to characterize the material behavior. Unstable plastic flow in 〈 1 0 0 〉 grains was seen to occur when loaded above 700 m s −1 free surface velocity. Observations of the grain boundary region showed that a smooth transition occurred between the elastic precursors in both grains as well as the plastic waves (when plastic flow is evident). Futhermore, the length of the transition zone across the boundary was observed to be larger than the projection of the boundary, indicating that refraction of the incident wave resulted in the initiation of transmitted and reflected waves. A model is developed to explain the experimentally observed behavior. The model describes the scattering of elastic–plastic waves off of grain boundaries in crystalline materials where slip is the active deformation mechanism. Reflected elastic release waves and transmitted plastic waves scattering at large angles (i.e. 56° for the transmitted wave) from the boundary are predicted for the case of an incident plastic wave propagating along 〈 1 1 1 〉 and impacting a 45° inclined boundary, which appears to be consistent with the experimental VISAR records. The case of an incident 〈 1 0 0 〉 plastic wave could not be treated since the incident polarization vector is either parallel or perpendicular to the operative slip vectors in NiAl.

Wave particles

We present a new method for the real-time simulation of fluid surface waves and their interactions with floating objects. The method is based on the new concept of wave particles, which offers a simple, fast, and unconditionally stable approach to wave simulation. We show how graphics hardware can be used to convert wave particles to a height field surface, which is warped horizontally to account for local wave-induced flow. The method is appropriate for most fluid simulation situations that do not involve significant global flow. It is demonstrated to work well in constrained areas, including wave reflections off of boundaries, and in unconstrained areas, such as an ocean surface. Interactions with floating objects are easily integrated by including wave forces on the objects and wave generation due to object motion. Theoretical foundations and implementation details are provided, and experiments demonstrate that we achieve plausible realism. Timing studies show that the method is scalable to allow simulation of wave interaction with several hundreds of objects at real-time rates.

2005年宮城県沖地震(&lt;I&gt;M&lt;/I&gt;7.2)に伴った地震時・地震後地殻変動から推定されたプレート境界面上のすべり分布

A typical interplate earthquake with M7.2 occurred on August 16, 2005 on the plate boundary off Miyagi Prefecture. Co- and post-seismic deformations associated with this event were investigated to reveal the causal interplate slips using continuous GPS data and geodetic inversion. The co-seismic slip distribution shows good agreement with that estimated by seismic waveform inversions. The major slip area is limited to the southeastern part of the rupture area of the 1978 Miyagi-oki earthquake (M7.4). The post-seismic slip extended uni-laterally to the southwest of the co-seismic slippage. These distinctive features both of the co- and post-seismic slips might be caused by the existence of the locked plate interface in the northern and southwestern parts of the 1978 rupture area, where seismogenic stress has not released yet.

Introduction to the special section for the 2005 M7.2 Miyagi-oki earthquake

An M=7.2 earthquake occurred on the plate boundary off Miyagi Prefecture, northeastern Japan, at 11:46 a.m. Japanese Standard Time on 16 August 2005, when the number of people returning to their homes after the holidays was at a peak. This earthquake resulted in the Japanese bullet train of Tohoku/Akita/Yamagata/Shinkansen falling out of service for half a day, and it took a whole day for the service to get back to normal. A suspended ceiling also fell at a public facility in Sendai city, and many people were injured. Overall, this earthquake injured 79 people, and caused partial damage to 339 buildings. Large earthquakes with a magnitude of ∼7.5 have occurred repeatedly at a recurrence interval of ‘37 years along the plate boundary off Miyagi Prefecture. When the M=7.2 event occurred in the source area of the anticipated Miyagioki earthquake, more than 27 years had passed since the last event, and the possibility of an earthquake occurrence within the next 10 years exceeded 50% according to the evaluation report by the Headquarters for Earthquake Research Promotion (2003) of the Japanese government. Among all of the anticipated earthquakes in Japan, this Miyagi-oki earthquake had the highest probability of occurrence. Although the August 2005 Miyagi-oki earthquake occurred within the source area of the anticipated Miyagioki earthquake, the magnitude was slightly smaller than M=7.5 that had been anticipated. For this reason, the Headquarters for Earthquake Research Promotion predicted that this earthquake is not the anticipated Miyagi-oki earthquake. However, if this 2005 earthquake is not the one anticipated—subsequently denoted here as the “coming” earthquake—when are we to expect the Miyagi-oki earthquake? Moreover, what is happening within the source area of the coming Miyagi-oki earthquake at this moment? It is critical for us to provide answers to those questions in order to get a clear picture of the coming Miyagi-oki earthquake. Dense nationwide seismic and GPS networks, which were recently constructed as the “Kiban” networks [in Japanese, this means the basic observation network (Okada et al., 2004; Sagiya, 2004)], were successful in recording the mainshock rupture, aftershock activity and post-

Co- and post-seismic slip associated with the 2005 Miyagi-oki earthquake (M7.2) as inferred from GPS data

Abstract A large earthquake with M7.2 occurred on August 16, 2005 along the plate boundary off Miyagi Prefecture. Co- and post-seismic deformations associated with this event were investigated to reveal the causal interplate slips using continuous GPS data and geodetic inversion. The coseismic slip distribution shows good agreement with that estimated by seismic waveform inversions. The major slip area is limited to the southeastern part of the rupture area of the previous 1978 event. The post-seismic slip extended to the southwest of the co-seismic slip area. These distinctive features of both the co- and post-seismic slips might be caused by the existence of the locked plate interface, where seismogenic stress has not released yet, in the northern part of the 1978 rupture area.

Coseismic slip distribution of the 2005 off Miyagi earthquake (M7.2) estimated by inversion of teleseismic and regional seismograms

Abstract A large earthquake (M7.2) occurred along the plate boundary off Miyagi Prefecture (Miyagi-Oki), northeastern Japan, on August 16, 2005. In this area, large earthquakes (~M7.5) have occurred repeatedly at intervals of about 37 years, and more than 27 years have passed since the last event occurred. To estimate the relationship between this earthquake and the previous events, we determined coseismic slip distribution by this 2005 Miyagi-Oki earthquake by adopting the seismic waveform inversion method of Yagi et al. (2004) and compared it with that of the previous 1978 Miyagi-Oki earthquake. We performed two cases of the inversions; inversion using only far-field seismograms and that using far-field seismograms and local seismograms simultaneously. Both results show that a large slip occurred near the hypocenter and rupture extended to the westward deeper portion. Considering that the rupture area of the 2005 event partly overlapped with the southeastern part of that of the 1978 event, suggests this result the possibility that plural asperities exist which cause the sequence of Miyagi-Oki earthquakes and that the 2005 event ruptured one of such asperities, although the previous 1978 event ruptured all the asperities at one time.

A frequency domain laser based ultrasonic system for time resolved measurement of broadband acoustic transients

A high-sensitivity frequency domain laser based ultrasonic system is presented which uses a low power, amplitude modulated continuous wave (cw) laser source for acoustic wave generation. The acoustic signals are detected using a path stabilized Michelson interferometer coupled to a rf lock-in amplifier. The modulation frequency of the generation laser is scanned over the bandwidth of interest, and transient acoustic signals are reconstructed from the frequency domain data. The effects of measurement frequency resolution, bandwidth, and time domain aliasing on the reconstructed transient response are discussed. Experimental results on thin plates, where diffuse acoustic wave fields lasting several hundred microseconds are seen as a result of multiple reflections off of sample boundaries, demonstrate that the time domain signal can be unambiguously reconstructed through appropriate selection of frequency resolution. Time domain reconstructions of acoustic signals over a bandwidth of 200MHz demonstrate the utility of the approach for acoustic microscopy; individual acoustic transients can be detected with extremely high signal to noise ratio and time gated for analysis.