Forearc density structure of the overriding plate in the northern area of the giant 1960 Valdivia earthquake

The objective of this work is to analyse the density structure of the continental forearc in the northern segment of the 1960 Mw 9.6 Valdivia earthquake. Regional 2D and local 3D density models have been obtained from available gravity data in the area, complemented by new gravimetric stations. Models are constrained by independent geophysical and geological information and new TEM and MT soundings. The results show a segmentation of the continental wedge along and perpendicular to the margin, highlighting a high-density anomaly, below the onshore forearc basin, that limits the late Paleozoic–early Mesozoic metamorphic basement in the region where Chaitenia terrane has been proposed. A progressive landward shift of this anomaly correlates with the high slip patch of the giant 1960 Mw 9.6 Valdivia earthquake. Based on these results, we propose that the horizontal extension of the less rigid basement units conforming the marine wedge and Coastal Cordillera domain could modify the process of stress loading during the interseismic periods, and also that changes in position and extension of the late Paleozoic–early Mesozoic accretionary complex could be linked with the frictional properties of the interplate boundary. This analysis provides new evidence of the role of the overriding plate structure in the seismotectonic process in subduction zones.

Thermohaline interleaving induced by horizontal temperature and salinity gradients from above

In this work we show that horizontal gradients of temperature and salinity with compensating effects on density can drive thermohaline intrusion in the fluid layer below. Specifically, different types of double diffusive convection generate differential vertical fluxes from the top boundary, which then sustain horizontal temperature and salinity gradients within the bulk. Interleaving layers develop in the bulk and slope downward towards the cold fresh side, which are of the diffusive type. New layers emerge near the bottom boundary and shift the existing layers upward due to the density difference induced by the divergence of the vertical fluxes through the top surface. Detailed analyses reveal that the present intrusion is consistent with those in the narrow fronts, and both layer thickness and current velocity follow the corresponding scaling laws. Such intrusion process provides an extra path to transfer heat and salinity horizontally towards the cold and fresh side, but transfer the density anomaly towards the warm and salty side. These findings extend the circumstances where thermohaline intrusions may be observed.

Dissecting a Zombie: Joint Analysis of Density and Resistivity Models Reveals Shallow Structure and Possible Sulfide Deposition at Uturuncu Volcano, Bolivia

The recent identification of unrest at multiple volcanoes that have not erupted in over 10 kyr presents an intriguing scientific problem. How can we distinguish between unrest signaling impending eruption after kyr of repose and non-magmatic unrest at a waning volcanic system? After ca. 250 kyr without a known eruption, in recent decades Uturuncu volcano in Bolivia has exhibited multiple signs of unrest, making the classification of this system as “active”, “dormant”, or “extinct” a complex question. Previous work identified anomalous low resistivity zones at <10 km depth with ambiguous interpretations. We investigate subsurface structure at Uturuncu with new gravity data and analysis, and compare these data with existing geophysical data sets. We collected new gravity data on the edifice in November 2018 with 1.5 km spacing, ±15 μGal precision, and ±5 cm positioning precision, improving the resolution of existing gravity data at Uturuncu. This high quality data set permitted both gradient analysis and full 3-D geophysical inversion, revealing a 5 km diameter, positive density anomaly beneath the summit of Uturuncu (1.5–3.5 km depth) and a 20 km diameter arc-shaped negative density anomaly around the volcano (0.5–7.5 depth). These structures often align with resistivity anomalies previously detected beneath Uturuncu, although the relationship is complex, with the two models highlighting different components of a common structure. Based on a joint analysis of the density and resistivity models, we interpret the positive density anomaly as a zone of sulfide deposition with connected brines, and the negative density arc as a surrounding zone of hydrothermal alteration. Based on this analysis we suggest that the unrest at Uturuncu is unlikely to be pre-eruptive. This study shows the value of joint analysis of multiple types of geophysical data in evaluating volcanic subsurface structure at a waning volcanic center.

Variabel Insitu Density Anomaly Untuk Aplikasi Fusi Oseanografi

Densitas massa air berkaitan dengan berat jenis. Dimana data info tentang densitas sangat dibutuhkan untuk perhitungan perbandingan berat jenis massa air yang akan dimasukkan ke bodi kapal selam dalam rangka mengatur keseimbangan kapal selam melayang di kolom air. Aplikasi Sistem Fusi Oseanografi telah berhasil dibangun pada tahun 2019. Aplikasi ini masih membutuhkan data-data Oseanografi yang lain yang mendukung keperluan sektor maritim secara umum dan sektor hankam secara khusus. Secara khusus di sektor hankam data karakteristik masa air laut umumnya diperlukan untuk perhitungan lanjutan variabel-variabel penting dari operasi militer bawah laut. Sebagai contoh operasi kapal selam, dan pemasangan ranjau bawah laut. Kedua contoh operasi tersebut memerlukan data dan informasi tentang densitas air laut. Penelitian ini bertujuan untuk 1) Melakukan perhitungan variabel densitas air laut terhadap kedalaman di 11 WFO dan di seluruh perairan Indonesia; 2) Memvisualisasikan variabel densitas di beberapa kedalaman secara bulanan dan tahunan; 3) Memutakhirkan webdatabase sistem fusioseanografi yang sudah terbangun dengan menambahkan variable densitas air laut (Insitu Density Anomaly) terhadap kedalaman, dengan menampilkan karakteristik densitas air laut secara tahunan maupun bulanan, selain itu ditampilkan sesuai region WFO dan di seluruh Perairan Indonesia; 4) Melakukan uji coba input dan output data densitas air laut (Insitu Density Anomaly) di aplikasi android sistem Fusioseanografi. Sistem aplikasi Fusioseanografi di android dapat di akses pada google play dengan link;

Anomalies from correlation functions in defect conformal field theory

In previous work, we showed that an anomaly in the one point function of marginal operators is related by the Wess-Zumino condition to the Euler density anomaly on a two dimensional defect or boundary. Here we analyze in detail the two point functions of marginal operators with the stress tensor and with the displacement operator in three dimensions. We show how to get the boundary anomaly from these bulk two point functions and find perfect agreement with our anomaly effective action. For a higher dimensional conformal field theory with a four dimensional defect, we describe for the first time the anomaly effective action that relates the Euler density term to the one point function anomaly, generalizing our result for two dimensional defects.

The anomalous behavior of liquids in three-dimensional and two-dimensional spaces

Using a molecular dynamics method water-like anomalies in a core-softened system depending on the potential parameters and space dimension were investigated. We have examined the anomalies of density, diffusion and structure and have shown that the sequence of anomalous regions cardinally depends on the repulsive step width and space dimension. Thus, in a three-dimensional (3D) system with small values of the step width the sequence of anomalous regions is the same as in water, whereas in a two-dimensional (2D) system – as in liquid silica. With an increase in the step width, an inversion of the regions of the diffusion anomaly and of the density anomaly is observed. Such an unusual sequence of anomalous regions different from water and liquid silica is exclusively caused by the step width and does not depend on the space dimension.

Forearc density structure of the overriding plate in the northern area of the giant 1960 Valdivia earthquake

The objective of this work is to analyse the density structure of the continental forearc in the northern segment of the 1960 Mw 9.6 Valdivia earthquake. Regional 2D and local 3D density models have been obtained from available gravity data in the area, complemented with new gravimetric stations. Models are constrained by independent geophysical/geological information and new TEM and MT soundings. The results show a segmentation of the continental wedge along and perpendicular to the margin, highlighting a high density anomaly, below the onshore forearc basin, that limits the Late Paleozoic-Early Mesozoic metamorphic basement in the region where Chaitenia terrain has been proposed. A progressive landward shift of this anomaly correlates with the high slip patch of the giant 1960 Mw 9.6 Valdivia earthquake. Based on these results, we propose that the horizontal extension of the less rigid basement units conforming the marine wedge and Coastal Cordillera domain could modify the process of stress loading during the interseismic periods, and also that changes in position and extension of the Late Paleozoic-Early Mesozoic accretionary complex could be linked with the frictional properties of the interplate boundary. This analysis provides new evidence of the role of the overriding plate structure on the seismotectonic process in subduction zones.

Lonosphere-thermosphere Relation as Seen in Measured and Modeled Electron and Neutral Densities

The availability of in-situ neutral and electron densities along the orbit of the satellite missions GRACE and CHAMP provide a good opportunity to study the ionosphere-thermosphere (IT) system. The aim of this paper is (1) to use these data sets, to study the IT density relation empirically via correlation properties for different conditions depending on solar activity, geomagnetic latitude, and local time and (2) to verify whether these relations are consistent with the output of the TIE-GCM model of the thermosphere and ionosphere. Our results show that the correlations of electron and neutral densities strongly depend on magnetic local time (MLT) with a minimal correlation between 6-9h MLT, e.g., every 131 days for CHAMP around 400km altitude and every 160 days for GRACE around 500km. During low solar activity, the correlation of modeled and measured densities agrees well for both satellites. On the contrary, we note that the correlations between the modeled values are higher, especially during high solar activity, where the difference between correlations of modeled and measured densities is about 0.2. We suggest that the reason for this misalignment might be related to the poor representation of the equatorial density anomaly in the model especially during high solar activity. We believe our results will be useful for studies that aim at assimilating electron densities into a physical model to improve the prediction of neutral densities, since the skill of data assimilation depends to a large extent on the representation of the correlation between both densities.

How the growth of ice depends on the fluid dynamics underneath

Convective flows coupled with solidification or melting in water bodies play a major role in shaping geophysical landscapes. Particularly in relation to the global climate warming scenario, it is essential to be able to accurately quantify how water-body environments dynamically interplay with ice formation or melting process. Previous studies have revealed the complex nature of the icing process, but have often ignored one of the most remarkable particularities of water, its density anomaly, and the induced stratification layers interacting and coupling in a complex way in the presence of turbulence. By combining experiments, numerical simulations, and theoretical modeling, we investigate solidification of freshwater, properly considering phase transition, water density anomaly, and real physical properties of ice and water phases, which we show to be essential for correctly predicting the different qualitative and quantitative behaviors. We identify, with increasing thermal driving, four distinct flow-dynamics regimes, where different levels of coupling among ice front and stably and unstably stratified water layers occur. Despite the complex interaction between the ice front and fluid motions, remarkably, the average ice thickness and growth rate can be well captured with the theoretical model. It is revealed that the thermal driving has major effects on the temporal evolution of the global icing process, which can vary from a few days to a few hours in the current parameter regime. Our model can be applied to general situations where the icing dynamics occur under different thermal and geometrical conditions.