Radar interferometry from the ALOS satellite captured the coseismic ground deformation associated with the 2010 Mw 8.8 Maule, Chile earthquake. The ALOS interferograms reveal a sharp transition in ...fringe pattern at ∼150 km from the trench axis that is diagnostic of the downdip rupture limit of the Maule earthquake. An elastic dislocation model based on ascending and descending ALOS interferograms and 13 near‐field 3‐component GPS measurements reveals that the coseismic slip decreases more or less linearly from a maximum of 17 m (along‐strike average of 6.5 m) at 18 km depth to near zero at 43–48 km depth, quantitatively indicating the downdip limit of the seismogenic zone. The depth at which slip drops to near zero appears to be at the intersection of the subducting plate with the continental Moho. Our model also suggests that the depth where coseismic slip vanishes is nearly uniform along the strike direction for a rupture length of ∼600 km. The average coseismic slip vector and the interseismic velocity vector are not parallel, which can be interpreted as a deficit in strike‐slip moment release.
For many practical applications, ranging from cadastre and engineering to scientific, GNSS locations must refer to a specific epoch in a known reference frame to establish a consistent spatial ...relationship between georeferenced features measured at different times. When an earthquake occurs, an effectively instantaneous coseismic offset in position is observed. This offset varies as a function of distance and direction from the earthquake’s rupture zone and depends on its type and magnitude. When GNSS is used to measure the position of a point after an earthquake, the result includes the coseismic displacement suffered by that point and this displacement must be removed to provide coordinates in the conventional epoch. When post-event GNSS observations are far from continuous GNSS monitoring stations, their coseismic displacements are unknown and must be estimated using surrounding continuous GNSS stations. Interpolation of coseismic displacements, however, is difficult unless a sufficiently dense continuous GNSS network exists, especially in the near-field. We present a methodology for estimating coseismic displacements in areas with low-density continuous GNSS coverage by using geophysical models in a hybrid (dynamic-kinematic) mode. We do this using elastic deformation of a spherical earth to constrain the overall coseismic displacement field without imposing the usual geodynamic constraints on fault slip distribution. Application of this methodology to the 2010 Maule and 2015 Illapel, Chile, earthquakes provides coseismic estimates on survey GNSS stations with rms (95% confidence interval) residuals of ~ 3 cm for Maule, and ~ 2 cm for Illapel. We also tested our models using InSAR and found that the models correctly predict the near-field deformation.
The marine portion of the West Antarctic Ice Sheet (WAIS) in the Amundsen Sea Embayment (ASE) accounts for one-fourth of the cryospheric contribution to global sea-level rise and is vulnerable to ...catastrophic collapse. The bedrock response to ice mass loss, glacial isostatic adjustment (GIA), was thought to occur on a time scale of 10,000 years. We used new GPS measurements, which show a rapid (41 millimeters per year) uplift of the ASE, to estimate the viscosity of the mantle underneath. We found a much lower viscosity (4 × 10
pascal-second) than global average, and this shortens the GIA response time scale from tens to hundreds of years. Our finding requires an upward revision of ice mass loss from gravity data of 10% and increases the potential stability of the WAIS against catastrophic collapse.
A European view of loess history is presented. The major events, or ‘great moments’, considered are (1) Karl Caesar von Leonhard names loess; (2) Charles Lyell popularises loess; (3) Richthofen ...solves ‘The Loess Problem’; (4) John Hardcastle relates loess to climate; (5) Pavel Tutkovskii makes clear the role of glaciers in loess genesis; (6) V.A. Obruchev makes the case for desert loess; (7) L.S. Berg propounds the ‘in-situ’ theory of loess formation; (8) Rudolf Grahmann maps loess in ‘Europa’; (9) R.J. Russell adopts the ‘in-situ’ idea; (10) Liu Tungsheng pioneers Chinese loess stratigraphy; (11) Julius Fink focuses loess research in the INQUA Loess Commission; and (12) George Kukla reshapes the Quaternary by way of loess research. The need for Chinese, Russian, and North American accounts to balance an authoritative view of loess history is recognized. The truly critical moment in the 20th century was the discovery by Liu Tungsheng and his colleagues of multiple palaeosols within the Chinese loess and the associated realization that these implied a multi-event Quaternary.
There are certain controls which operate to demarcate the nature and size range of quartz particles in terrestrial detrital sediments. The particles fall into discrete and definable populations, ...which are separated by ‘Tanner gaps’. Quartz sand nature is determined largely by a eutectic-like reaction, which takes place in the original igneous rock. This reaction delivers a fine mix of quartz and feldspar units, which on weathering deliver quartz sand. The formation of quartz silt is more contentious; it appears that silt production is essentially controlled by the presence in larger quartz particles of ‘Moss defects’, crystalline defects introduced into the quartz structure by earlier events, e.g. the high-low displacive transformation in cooling quartz. There appear to be two modes in airborne quartz particles (which have been called large dust and small dust). The larger mode is the loess mode (around 20–60 μm) and the smaller mode falls into the classification with high-level, long-travel dust (mode around 2–6 μm). The quartz in small dust is around the same size as the clay mineral agglomerate particles (CMA) which form a considerable proportion of high level dust clouds. The CMA particles form from lake deposits; the size is controlled by the openness of the packing in the lake sediments. This can be demonstrated by a simple Monte Carlo model.
There are large problems of irrigation, hydrocollapse and soil erosion associated with the loess deposits of Central Asia. To get to grips with these we need a clear view of the nature and formation ...of the loess, and in this region there are still disputes and disagreements and controversies. Important events in the loess deposit formation process can be identified and studied, and relative significances assigned. There are large loess deposits in the vicinity of Tashkent, in the north-east of Uzbekistan. These were mapped and studied for many years by G.A. Mavlyanov and associates; they used a terminology which appears to be based on Pavlov's nineteenth century usage and developed a ‘polygenetic’ formation theory for loess deposits. This was a formation theory very much associated with Central Asia and essentially favouring a ‘proluvial’ mechanism. A speculative look at the deposits near Tashkent allows alternative terminologies and formation mechanisms to be considered. In particular the widespread Soviet antipathy to aeolian deposition can be examined. The deposits associated with the Chirchik river, upstream of Tashkent, might be affected by the Pavlov mechanisms, but could be topped by aeolian deposits. The collapse of loess when wetted is controlled by the nature of the ground and is a very significant interaction of soil and water, in particular in Central Asia. Hydrocollapse and water erosion are closely related and are controlled by the complex nature of loess ground. Dust clouds in eastern Uzbekistan are largely loess related, but in the west dust material is raised from the drying Aral Sea bed; this is often clay mineral agglomerate material and can carry dangerous pollutants.
The fractal is presented as a method for describing the geometry of particles, with particular reference to the breakdown of granular soils and the formation of loess. The preliminary results are ...reported: (a) for the extent to which silt due to comminution exhibits a fractal distribution; (b) the tendency of fractal dimension to change with the comminution process; and (c) the relationship between fractal dimension describing particle size distribution and the grinding time. Laboratory simulation confirms the general tendency of fractal characteristics to reflect the size reduction process.
Loess and loess-like deposits were much studied in the Soviet Union, and are currently under investigation in Russia and surrounding countries. There is a vast literature in Russian, which touches on ...all aspects of loess science and technology. In particular, the studies of the origin of collapsibility are almost totally in Russian, and of course studies on the various regions of Russia and the countries of the Former Soviet Union FSU appear in Russian. This review looks at the literature in Russian and attempts to pick out key contributors, major topics and works and to identify the critical regions and zones of investigation. Because so many regions of the FSU had people living on loess ground, there is a vast literature on engineering geology and ground engineering topics, and this tends to dominate all the literature on loess in Russian. Following Russian practice, the fine-grained deposits under consideration are divided into loess and loess-like deposits. Three main topics are recognised across the whole spectrum of loess research: formation and distribution of loess deposits; stratigraphy, cyclicity and palaeoclimatology; and engineering topics, in particular hydrocollapse and subsidence, and we concentrate on the engineering geology topics. An attempt is made, based on the map of Abelev and Abelev Abelev, Yu.M., Abelev, M.Yu., 1968. Fundamentals of design and construction on collapsible macroporous soils, 2nd ed. Stroiizdat, Moscow, 431 pp. (in Russian) of collapsing loess deposits, to define seven loess regions within the geographical limits of the old USSR. The seven regions are those where geotechnical problems might be expected.
The particles in finer-grained detrital sediments are usually composed of quartz. They fall into two size grades: sand (2 mm–62 μm) and silt (62 μm–2 μm). These size gradings conceal important ...geological processes since there are geological controls on both the quartz sand and silt populations. Sand nature is largely controlled by geochemical reactions, for example in cooling granite from which it is eventually released by weathering action. The quartz is among the last part of the rock system to solidify and the eutectic-like reaction which occurs ensures that the quartz exists as small crystalline units, each suffering considerable cooling and recrystallisation stresses. Silt is broken quartz, and has traditionally been considered to lack a specific geological control. The situation is confused by the large range of materials that fall into the size category, but there do seem to be distinguishable modes and possibly comminution limits within the 60 μm span. The controls operating in this size range are probably the critical concentration of `Moss' defects in the quartz particles. Moss postulated the formation of specific crystal defects in the quartz formed in granites. These affect sand formation and it is possible that they also control the mode size of silt particles. Within the silt range there may be several usefully definable populations, as Moss proposed for sand. The Quaternary appears to be a silt-rich period due to tectonic and glacial activity, but silt production is apparent throughout the sedimentary record. Very long-term silt producing processes are required. To produce silt in nature, on a large scale, very energetic processes are required. Many processes that are believed to generate silt particles have been listed. However, large-scale production is essentially due to glacial grinding, or to intense weathering processes in high, cold, tectonically active mountain regions. The region of High Asia (of crustal overlap) is a major generator of silt particles. These form the productive alluvial soils of north India, most of the nation of Bangladesh, the loess deposits along the Syr-darya and Amu-darya rivers in Central Asia, and the great loess deposits of North China. Some claims have been made for silt production in hot deserts. Large amounts of very fine aerosolic dust are produced, but in terms of loess-sized particles this is a small-scale process and leads to modest, disputed deposits. The loess deposits around the Sahara usually have smaller mode sizes (e.g., Nigeria) or larger mode sizes (e.g., Libya, Tunisia) than the true Chinese mode at 25 μm. This paper aims to introduce the distinguishing properties of sand and silt, discuss in detail the possible processes of silt formation in relation to the evidence of what is produced, describe the major silt populations, and conclude on the most likely formation process(es). In particular three silt ranges are discussed in relation to the
R-size diagram: C, 2–5 μm, D
1, 20–30 μm, and D
2, ∼60 μm. These can represent Canadian quickclay (QQ), Chinese loess and the ideal Loughborough Loess (LL) and North African loess (NAL). It is intended that this paper will put into context the diverse work in the area, and in so doing shed light on what is an often overlooked subject.
In 1970 G.A. Mavlyanov, in Tashkent, published his proposed set of research topics for workers on loess in engineering geology. They concerned (1) formation theory, (2) property variations, (3) ...property/genesis correlations, (4) standard terminology, (5) classification, (6) formation vs. environment, (7) water/property relationships, (8) irrigation, (9) collapse management, (10) collapse theory, (11) collapse forecast in irrigation, (12) equipment development, (13) very high sensitivity studies, (14) collapse in seismic areas, (15) micro-seismic zoning. The proposals were not widely appreciated; now there is a chance to present a translation into English, an updating and a commentary on the key concepts. Proposal 1 was the longest on the original list and receives most discussion—it is here that the maximum reconciliation is required—between approaches to loess formation.
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