Deep Discontinuity Research Articles

Analysis of Structural Information from Aftershock Clouds—A Case Study of the 2008 Ms 8.0 Wenchuan Earthquake

Abstract We present a method to quantitatively analyze the characteristics of clusters and extract cluster centers in aftershock clouds to study the corresponding structural information. Based on a cluster center approach, a 3D rupture surface is constructed based on the aftershocks of the Wenchuan earthquake. The geometric characteristics of the rupture surfaces show that the Longmenshan fault zone should be divided into seven segments from south to north, and for most of the rupture surfaces, there are two discontinuities at depths of 10 and 20 km. According to the cluster characteristic distance of each rupture branch, the number of aftershocks within the cluster distance is counted. The statistical results show that 22% of the aftershocks of the Wenchuan earthquake occurred on the rupture surface parallel to the main fault and that the rest occurred along other nonparallel rupture surfaces or were scattered. The complex branches of rupture surfaces and the existence of rupture surfaces penetrating the 10 km deep discontinuity layer are two common characteristics of the XI intensity area. The change in tendency of the fracture surface between depths of 10 and 20 km may restrain the continued northward extension of the XI intensity area.

Seismic evidence for a 1000 km mantle discontinuity under the Pacific

Seismic discontinuities in the mantle are indicators of its thermo-chemical state and offer clues to its dynamics. Ray-based seismic methods, though limited by the approximations made, have mapped mantle transition zone discontinuities in detail, but have yet to offer definitive conclusions on the presence and nature of mid-mantle discontinuities. Here, we show how to use a wave-equation-based imaging method, reverse-time migration of precursors to surface-reflected seismic body waves, to uncover both mantle transition zone and mid-mantle discontinuities, and interpret their physical nature. We observe a thinned mantle transition zone southeast of Hawaii, and a reduction in impedance contrast around 410 km depth in the same area, suggesting a hotter-than-average mantle in the region. Here, we furthermore reveal a 4000–5000 km-wide reflector in new images of the mid mantle below the central Pacific, at 950–1050 km depth. This deep discontinuity exhibits strong topography and generates reflections with polarity opposite to those originating at the 660 km discontinuity, implying an impedance reversal near 1000 km. We link this mid-mantle discontinuity to the upper reaches of deflected mantle plumes upwelling in the region. Reverse-time migration full-waveform imaging is a powerful approach to imaging Earth’s interior, capable of broadening our understanding of its structure and dynamics and shrinking modeling uncertainties.

A Matching Optimization Algorithm About Low-Altitude Remote Sensing Images Based on Geometrical Constraint and Convolutional Neural Network

This article presents a novel matching optimization algorithm for low-altitude remote sensing images based on a geometrical constraint and a convolutional neural network (CNN). The proposed method was designed to be effective in enhancing the integrity and accuracy of point clouds generated by stereo matching. To overcome the limitations of stereo matching, we trained a CNN to predict how well image patches match and used it in patch optimization. The main advantage of this approach is that the proposed algorithm can decrease the mismatching and errors caused by noise, deep discontinuity, and weak texture in low-altitude remote sensing images and can reconstruct an integrated and accurate point cloud. Comparative studies and experimental results validate the accuracy of the proposed algorithm when used for dense point generation from low-altitude remote sensing images.

Disposition of magmatic eruptions and fault distribution in northwestern Saudi Arabia using pseudo-depth slice magnetic anomaly

AbstractThis study presents the disposition of magmatic eruptions with a fault distribution in northwestern Saudi Arabia, where intensive magma invades the lithosphere. Structural and magmatic features are traced at successive depths through high-resolution magnetic anomaly pseudo-depth slices. The total horizontal gradient technique is applied to pseudo-depth slice magnetic anomalies to enhance the linear trends of faults and related magmatic activity. A comprehensive cross-section constructed from the projection of gradient horizontal maxima relative to pseudo-slices allows the visualization of the vertical behavior of faults and magma sources. Three major fault systems were identified, primarily aligned in the N–S, NE–SW and NW–SE directions. They are characterized by increasing length and width with depth. The N-S fault system is a major non-planar deep system throughout the area, affected by the NW–SE and NE–SW deep discontinuities. The evolution of these discontinuities with depth successfully shows magma uprising zones represented by a circular horizontal gradient, which starts to appear at a depth of 4500 m with a vertical continuity to the surface. They are interpreted as possible locations of ascending magma chambers or vents. The disposition of these magma sources with fault distribution can show a close relationship between the fault systems and the magma eruptions. The interpreted magma vents appear where the NE-trending transform faults intersect the NW or N–S fault zone. These intersections may represent weak zones that act as vertical conduits through which magma discontinuously erupts into the overlying crust, forming major volcanic fields in the eastern Red Sea.

Complicated Lithospheric Structure Beneath the Contiguous US Revealed by Teleseismic S‐Reflections

AbstractLithospheric discontinuities, including the lithosphere‐asthenosphere boundary (LAB) and the enigmatic mid‐lithospheric discontinuities (MLDs), hold important clues about the structure and evolution of tectonic plates. However, P‐ and S‐receiver‐function (PRF and SRF) techniques, two traditional techniques to image Earth's deep discontinuities, have some shortcomings in imaging lithosphere discontinuities. Here, we propose a new method using reflections generated by teleseismic S waves (hereafter S‐reflections) to image lithospheric discontinuities, which are less affected by multiple phases than PRFs and have better depth resolution than SRFs. We apply this method to the data collected by the Transportable Array and other regional seismic networks and obtain new high‐resolution images of the lithosphere below the contiguous US. Beneath the tectonically active Western US, we observe a negative polarity reflector (NPR) in the depth range of 60–110 km, with greatly varying amplitude and depth, which correlates with active tectonic processes. We interpret this feature as the LAB below the Western US. Beneath the tectonically stable Central and Eastern US, we observe two NPRs in the depth ranges of 60–100 km and 100–150 km, whose amplitude and depth also vary significantly, and which appear to correlate with past tectonic processes. We interpret these features as MLDs below the Central and Eastern US. Our results show reasonable agreement with results from PRFs, which have similar depth resolution, suggesting the possibility of joint inversion of S‐reflections and PRFs to constrain the properties of lithospheric discontinuities.

Constraints on Thermal History of Mars From Depth of Pore Closure Below InSight

AbstractPlanetary crusts undergo viscous closure of pores at depth; if the thickness of this porous layer can be measured, constraints on crustal thermal evolution can be derived. We apply a pore closure model developed for the Moon to Mars and take into account the geological processes that may alter the depth of this transition region. If the 8–11 km deep discontinuity in seismic wave speed detected by the InSight lander marks the base of the porous layer, the heat flux at the time the porosity was created must have exceed 60 mW m−2, probably indicating a time prior to 4 Ga.

Sharpness of the paired 660-km discontinuity beneath the Izu-Bonin area

The 660-km discontinuity that separates the Earth's upper and lower mantle has primarily been attributed to phase changes in olivine and other minerals. Resolving the sharpness is essential for predicting the composition of the mantle and for understanding its dynamic effects. In this study, we used S-to-P conversions from the 660-km interface, termed S660P, arriving in the P-wave coda from one earthquake in the Izu–Bonin subduction zone recorded by stations in Alaska. The S660P signals were of high quality, providing us an unprecedented opportunity to resolve the sharpness of the discontinuity. Our study demonstrated, based on the impedance contrast given by the IASP91 model, that the discontinuity has a transitional thickness of ~5 km. In addition, we observed a prominent arrival right after the S660P, which was best explained by S-to-P conversions from a deeper discontinuity at a depth of ~720 km with a transitional thickness of ~20 km, termed S720P. The 720-km discontinuity is most likely the result of a phase transition from majoritic garnet to perovskite in the segregated oceanic crust (mainly the mid-oceanic ridge basalt composition) at the uppermost lower mantle beneath this area. The inferred phase changes are also consistent with predictions from mineral physics experiments.

Farmland Use Transitions After the CAP Greening: a Preliminary Analysis Using Markov Chains Approach

This paper represents a preliminary attempt to evaluate ex-post impact of the CAP greening payment on farmland use changes, testing by a Markov Chain approach whether farmland use transitions dynamics changed after the introduction of this new policy instrument. Unlike previous contributions, relying on ex-ante simulations, this analysis is based on the actual behaviour of farmers over the period immediately after the last CAP reform. Such ex-post assessment was based on real georeferenced data on farmland allocation, collected in the Lombardy Region, in Northern Italy, over the period 2011-2016. As the current CAP has recently entered in force (in 2015), the present analysis covers the first two years of implementation of the new rules along with the previous four years. Results are in line with previous ex-ante simulations in the same region, detecting a deep discontinuity for those farmland uses characterised by monoculture before the introduction of the greening. They show a significant discontinuity of farmland use transitions in the reference area after the introduction of greening rules, pointing to a decrease in maize monoculture, in favour of other cereals and legume crops like soybean and alfalfa. Unlike some critical opinions that see current greening rules as a “low profile” compromise, the present analysis points to a strong effect of such rules on regions with high-intensity agriculture.

Crustal Formation on a Spreading Ridge Above a Mantle Plume: Receiver Function Imaging of the Icelandic Crust

AbstractIceland sits astride a mid‐ocean ridge underlain by a mantle hot spot. The interplay of these two geological processes has the potential to generate a complex and laterally variable crustal structure. The thickness of the Icelandic crust is a long running and controversial debate, with estimates ranging from a thin 20‐km crust to a thick 40‐km crust. We present new images of the first‐order seismic discontinuity structure of the Icelandic crust based on a joint inversion of receiver function and ambient noise‐derived surface wave dispersion data. Inversion results are validated through comparison to receiver functions multiphase common conversion point stacks across the densely instrumented Northern Volcanic Zone. We find a multilayered crustal structure consisting of a 6‐ to 10‐km‐thick upper crust underlain by either one or two discontinuities. The shallower discontinuity is found at depths of ≈20 km throughout Iceland. The deeper discontinuity is only present in some regions, defining the base of a lens‐like lower layer with maximum depths of 44 km above the center of the mantle plume. Either of these two discontinuities could be interpreted as the seismic Moho, providing an explanation why previous estimates of crustal thickness have diverged. Such structure may form via underplating of a preexisting oceanic crust as has been hypothesized in other ocean island plume settings. However, we demonstrate with a simple petrological model that variability in seismic discontinuity structure can also be understood as a consequence of compositional variation in melts generated with distance from the plume center.

Seismic constraints on the radial dependence of the internal rotation profiles of sixKeplersubgiants and young red giants

Context : We still do not know which mechanisms are responsible for the transport of angular momentum inside stars. The recent detection of mixed modes that contain the signature of rotation in the spectra of Kepler subgiants and red giants gives us the opportunity to make progress on this issue. Aims: Our aim is to probe the radial dependance of the rotation profiles for a sample of Kepler targets. For this purpose, subgiants and early red giants are particularly interesting targets because their rotational splittings are more sensitive to the rotation outside the deeper core than is the case for their more evolved counterparts. Methods: We first extract the rotational splittings and frequencies of the modes for six young Kepler red giants. We then perform a seismic modeling of these stars using the evolutionary codes CESAM2k and ASTEC. By using the observed splittings and the rotational kernels of the optimal models, we perform inversions of the internal rotation profiles of the six stars. Results: We obtain estimates of the mean rotation rate in the core and in the convective envelope of these stars. We show that the rotation contrast between the core and the envelope increases during the subgiant branch. Our results also suggest that the core of subgiants spins up with time, contrary to the RGB stars whose core has been shown to spin down. For two of the stars, we show that a discontinuous rotation profile with a deep discontinuity reproduces the observed splittings significantly better than a smooth rotation profile. Interestingly, the depths that are found most probable for the discontinuities roughly coincide with the location of the H-burning shell, which separates the layers that contract from those that expand. These results will bring observational constraints to the scenarios of angular momentum transport in stars.

CONSTRAINTS ON SUBDUCTION GEODYNAMICS FROM SEISMIC ANISOTROPY

AbstractMuch progress has been made over the past several decades in delineating the structure of subducting slabs, but several key aspects of their dynamics remain poorly constrained. Major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology, slab hydration and dehydration, mechanical coupling between slabs and the ambient mantle, the geometry of mantle flow above and beneath slabs, and the interactions between slabs and deep discontinuities such as the core‐mantle boundary. Observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy: when mantle rocks are deformed, a preferred orientation of individual mineral crystals or materials such as partial melt often develops, resulting in the directional dependence of seismic wave speeds. Measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems. Here I review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge, slab, and sub‐slab anisotropy. I also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations. I evaluate different models in light of constraints from seismology, geodynamics, and mineral physics. Finally, I discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress, particularly in frontier areas such as understanding slab dynamics in the deep mantle.

Educational Horizons of Contemporary Pakistan

When we glance at the intellectual horizons of Pakistan, what appears before our eyes is an intractable mAalA©e of inconsistent and often conflicting systems, riven by deep fissures and pervasive discontinuities. This situation, not unlike that in practically any contemporary Muslim society, does not mean that there is any inherent or actual intellectual inferiority in these societies. Pakistan itself can boast a vast treasure of talents, skills, and rigor of intellect. But it does engender a marked fragmentation of the country’s population.

Thinking things and feeling things: on an alleged discontinuity in folk metaphysics of mind

According to the discontinuity view, people recognize a deep discontinuity between phenomenal and intentional states, such that they refrain from attributing feelings and experiences to entities that do not have the right kind of body, though they may attribute thoughts to entities that lack a biological body, like corporations, robots, and disembodied souls. We examine some of the research that has been used to motivate the discontinuity view. Specifically, we focus on experiments that examine people's aptness judgments for various mental state ascriptions to groups. These studies seem to reveal that people are more inclined to think of groups as having intentionality than as having phenomenology. Combined with the fact that groups obviously lack a single biological body, this has been taken as evidence that people operate according to the relevant discontinuity. However, these studies support discontinuity only on the assumption that the experimental participants are interpreting the relevant group mental state ascriptions in a specific way. We present evidence that people are not interpreting these ascriptions in a way that supports discontinuity. Instead, we argue that people generally interpret group mental state ascriptions distributively, as attributions of mental states to various group members.

Delineating deep basement discontinuities of Qarun Lake Area, Egypt

The current study is mainly concerned with the description and analysis of the available aeromagnetic anomalies using different methodologies. Some structural elements could be deduced from the qualitative interpretation of such magnetic anomalies. The analysis of the worked magnetic maps, which included the total intensity magnetic map, reduced to-pole map, upward-continued maps, downward-continued maps, anomaly separation based on their wavelengths, or anomaly widths and enhanced horizontal gradient filtering aided in divulging the structural regime of the basement rocks, as well as the shallower features. As a result of the investigation, a basement tectonic map of the study area was constructed. This map shows that the area is portrayed by the presence of several major alternating basement swells and troughs in belts trending ENE–WSW, N–S, NE–SW and E–W. These major trends with the other minor trends dissected the basement surface into several tilted fault blocks forming anticlinal and synclinal zones with various depths and directions. These structural elements are shown in the basement tectonic map, and named Camel Pass-Abu Roash high, El-Sagha high, El Faras-El faiym high and Qattrani-El Gindi low trends.

Information theory–based measures of similarity for imaging shallow-mantle discontinuities

Mode conversions, such as the P-to-s (Ps) converted waves, are now employed in a routine manner to image the velocity boundaries in Earth9s interior. However, there exists an ambiguity in establishing shallow-mantle velocity discontinuities in the depth range 100–300 km through the Ps receiver function approach. This primarily stems from overlap in the time windows of arrivals of direct converted phases from the target depth boundaries (∼100–300 km depth) and reverberations originating from shallow structures (e.g., from crust and/or shallow lithosphere layers). Attempts have been made to address this problem. Classically, limited success has been achieved through methods such as the move-out, which are essentially performed in the measurement space. Recognizing this, we explore generic space-related information theory measures of similarity to extract diagnostics of discrimination between the primary converted waves and the multiply reflected arrivals in Ps receiver functions. Various measures of similarity, such as the mutual information (MI), and associated normalized distance measures, like the normalized variation of information (NVI) and normalized information distance (NID), are successfully applied to receiver function data sampling regions of different tectonic regimes of wide antiquity. Our seismological stations are located in the Archean-Proterozoic craton–mobile belt regions of SE India, Canada, and Phanerozoic United States. Significantly, at several locations in SE India, we interpret the unambiguous presence of midlithospheric discontinuities for the first time. We also either reconfirm or negate the presence of midlithospheric discontinuities beneath stations FFC (Flin Flon) and HRV (Harvard) located in North America. This study reinforces the presence of significant velocity contrast features related to the Lehmann discontinuity depth beneath the Precambrian cratonic stations of India (Hyderabad and Cuddapah) and the Phanerozoic Pasadena station in the United States. Further, multiple deep discontinuities of opposing velocity contrasts are delineated at depths of ∼275 km and ∼320 km beneath station PAS (Pasadena). Our results therefore show tremendous potential to unambiguously detect and distinguish between direct converted seismological phases and multiple reverberations. These information theory approaches discriminate the seismic phases unequivocally. This new approach thus complements the S-to-p (Sp) receiver function technique, which is suitable for detection of shallow-mantle discontinuities (midlithospheric discontinuities, lithosphere-asthenosphere boundary, Lehmann, etc.).

Molecular genetic evidence of a deep phylogenetic discontinuity between the asian and european races of pygmy wood mouse based on the mitochondrial cytochrome b gene variation

The variation of mitochondrial DNA (mtDNA) cytochrome b gene sequences of pygmy wood mouse Sylvaemus uralensis (Pallas, 1811) from local populations of European Russia, West Siberia, and neighboring countries (Moldova, Kazakhstan, Uzbekistan, and Turkmenistan) has been studied. Phylogenetic analysis based on our results and GenBank data revealed two clusters of haplotypes: the Western clade, which was reliably subdivided into two sequence groups, and the Eastern clade with no significant differentiation. The clusters corresponded exactly to the European and Asian races of pygmy wood mouse recognized previously on the basis of biochemical and karyotypic variation. We suppose that the Asian race can be considered as an independent allopatric species. This concept is supported by the following evidence: the high interrace divergence level suggesting more than 1 Ma of divergent evolution, the absence of common haplotypes and the hiatus between the main peaks of the mismatch distribution, difference in the codon usage frequencies, fixed nucleotide substitutions in cyt b, as well as different amino acid sequences of cytochrome b. Only specimens of the western phylogenetic lineage should be classified as S. uralensis (Pallas, 1811), while S. tokmak, according to its first description (Severtsov, 1873), may be considered as the species uniting specimens of the eastern phylogenetic lineage.

Seismic discontinuities in the mantle transition zone and at the top of the lower mantle beneath eastern China and Korea: Influence of the stagnant Pacific slab

We have analyzed broadband data to identify and determine mantle discontinuities in the mantle transition zone (MTZ) beneath eastern China, where the Pacific slab is stagnant. The depths of the 410 and 660km discontinuities are generally shallower and deeper, respectively, than the global averages in and near the Pacific slab beneath eastern China. The MTZ is thicker in the slab than the global average. This observation is consistent with the thermally controlled olivine to wadsleyite transformation for the 410km discontinuity and the post-spinel transformation for the 660km discontinuity. Other discontinuities appear from 690 to 750km in the lower mantle part of the Pacific slab. Recent mineralogical experiments indicate that the most plausible interpretation of these deep discontinuities is that they represent the ilmenite to perovskite transformation in a cold environment, such as that in the Pacific slab.

Where do innovations come from? Transformations in the US economy, 1970–2006

In the 1970s, there was a lively debate on both sides of the Atlantic about deep discontinuities in the development of advanced market societies. Much of this debate centered on the idea of postindustrial society-emphasizing a shift from goods to services and the rise of science-based production. A wide range of scholars argued that U.S. society, in particular, required significant institutional changes to take advantage of these new productive possibilities (Bell 1973; Brick 2006; Touraine 1971). Parallel arguments for discontinuity were made by theorists of fifty-to sixty-year economic long waves (Mandel 1980) and by contributors to regulation theory, who also argued that capitalist societies required new regulatory structures (Aglietta 1979).1 These arguments continued into the next decade, as reflected in the wide interest generated by Piore and Sabel’s argument in the Second Industrial Divide (1984) for a fundamental shift in the organization of production.

Darwin's last word: How words changed cognition

AbstractAlthough Penn et al. make a good case for the existence of deep cognitive discontinuity between humans and animals, they fail to explain how such a discontinuity could have evolved. It is proposed that until the advent of words, no species had mental representations over which higher-order relations could be computed.

Splitting of the 520-Kilometer Seismic Discontinuity and Chemical Heterogeneity in the Mantle

Seismic studies indicate that beneath some regions the 520-kilometer seismic discontinuity in Earth's mantle splits into two separate discontinuities (at approximately 500 kilometers and approximately 560 kilometers). The discontinuity near 500 kilometers is most likely caused by the (Mg,Fe)2SiO4 beta-to-gamma phase transformation. We show that the formation of CaSiO3 perovskite from garnet can cause the deeper discontinuity, and by determining the temperature dependence for this reaction we demonstrate that regional variations in splitting of the discontinuity arise from variability in the calcium concentration of the mantle rather than from temperature changes. This discontinuity therefore is sensitive to large-scale chemical heterogeneity. Its occurrence and variability yield regional information on the fertility of the mantle or the proportion of recycled oceanic crust.