Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra

Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records

The moment method used to infer stress from fault/slip data in sigma space: invalidity and modification

The moment method has recently been used to infer stress in sigma space from fault/slip data. However, if these data are distributed along a hyperplane having a smaller dimension than that of the space minus one, due to limited fault/slip population or biased sampling of it, the best solution of stress vector is not in most cases, as expected, the eigenvector of the datum matrix relating to the smallest eigenvalue. The solution lies within the subspace composed of the eigenvectors relating to the small eigenvalues, for which some auxiliary constraints need to be included. Shear sense constraint alone is adopted, and incorporated by way of grid search, which gives rise to a range of accepted stress vectors in the subspace. Examples from the Chelungpu fault, Taiwan, illustrate the feasibility of the proposed scheme

A hierarchical cluster approach for forward separation of heterogeneous fault/slip data into subsets

A new simple method of stress inversion uses hierarchical cluster analysis for forward separation of heterogeneous fault/slip data into subsets. Fault/slip data are classified into homogeneous fault classes, and a clustering routine classifies these into subsets. The method includes a way of discarding some residual data at the first stage that makes it fairly easy to recognize and eliminate some spurious fault data. However, this method is a type of hard division that overlooks the indeterminate nature of fault data. The more heterogeneous the data, the larger the calculation needed to find from a K-data set the homogeneous fault class that agglomerates a pair of 5-data subsets, sampled in a binomial distribution, with the maximum similarity in estimated stress vector between them. The K-data set is a working data group successively taken from the whole data. Given P phases of different stress state, the minimum value of K is 5P+1. Results from applying the method to two examples, artificial and real, demonstrate the feasibility of the method

On the use of imaginary faults in palaeostress analysis

The imaginary fault refers to the counterpart of a certain given fault that has a similar expression about the Wallace Bott hypothesis. It is included to further reduce the feasible fields for the principal stress directions using the right dihedra method. The given fault and its imaginary fault have a similar dip-slip sense under the extensional or compressional regime but, as proved in this paper, a different dip-slip sense under the strike-slip regime. Their relation in dip-slip sense does no change with the rotation of the coordinate system, thus making possible the general use in the reduction of the imaginary faults under any tectonic regime. A procedure for this use is proposed and applied to a real example to demonstrate the feasibility of this method. (C) 2017 Elsevier Ltd. All rights reserved

Synthetic slip plane, the combination of a pair of twinned and untwinned e-planes in a single calcite crystal: Application in dynamic analysis

This paper defines a synthetic slip plane as the linear combination of a pair of twinned and untwinned e-planes in a single calcite crystal. This auxiliary slip plane can be used together with the twinned e-plane either to further constrain the extents of the compression and tension axes in graphic dynamic analysis or to better estimate the reduced stress in numerical dynamic analysis. In this paper we proposed the novel method that solves for the reduced stress by maximizing the sum of the shear stress along the slip line on each twinned e-plane or synthetic slip plane under the constraint of the 1-valued second stress invariant. This new method yields an analytical solution of stress. It is applied to a series of artificial examples without any measurement error generated under the prescribed stresses. The estimated stresses are generally accurate and robust, which illustrates the feasibility of this new method

A Multilayer Rubber Board Radar Absorbing Material

Based on the theory of impedance matching, a multilayer absorbing material with the "pitfall" structure was designed. The multilayer absorbing material with 5 layers was obtained by optimization of the schemes, and the material shows 2 absorbing peaks in the broadband of 2~18 GHz frequencies. The peak in high frequencies can be adjusted with no effect on the peak in low frequencies through changing the thickness of the fifth layer. The changes of input impedances were displayed by analyzing the impedance chart. The prepared multilayer absorbing material was named JB-5, which processes the reflectivity no more than -12 dB in 6~17 GHz with the thickness no more than 5 mm and a good performance of standing the environment. The absorbing material can be produced in laboratory and pasted on surfaces of target with special adhesive by trimmed into required shapes so as to reduce the reflection of electromagnetic waves effectively

Paleostress Analysis from Calcite Twins at the Longshan Dome (Central Hunan, South China): Mesozoic Mega-Fold Superimposition in the Reworked Continent

It is generally accepted that during the Mesozoic NE−NNE-trending folds overprinted E−W-trending folds to form the Longshan dome in the central South China continent, although the interference map does not tell the relative ages of the fold sets. In an effort to deepen our understanding of the process of reworking the continent, paleostress analysis using calcite twins was carried out in this study to verify or falsify this model. Ten limestone samples were collected from Upper-Paleozoic limestones on the flanks of the dome and were measured using the universal stage for calcite e-twins. E-twins in the samples are divisible into two kinds, thick (≥1 μm) and thin (<1 μm), indicative of relatively higher and lower deformation temperatures, respectively. Stress estimates obtained using the improved version of Shan et al.’s (2019) method were grouped into two layer-parallel shortening (LPS) subsets and three non-LPS subsets. These subsets comprise four tectonic regimes: NWW−SEE compression (LPS1 and non-LPS1), NNE−SSW compression (LPS2 and non-LPS2), NW−SE extension (non-LPS3a) and NNE−SSW extension (non-LPS3b). They were further arranged in a temperature-decreasing order to establish a complex deformation sequence of the study area. In the sequence NE−NNE-trending folds have an older age than E−W-trending folds, something different from the model. The approximately N−S regional compression responsible for the former folds should have a profound effect on the intensely deformed continent, something ignored in earlier work