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This paper presents analysis of geomorphological indices for predicting the maximum observed earthquake (MOb‒Max) in research region, conducted in three steps: (i) determination of the magnitude of completeness (Mc) of the study area; (ii) assessment of the sensitivity of the geomorphological indicators (10 indices) to earthquake magnitude prediction; (iii) determination of the MOb–Max value. With a multilayer perceptron (MLP) neural network model with one hidden layer (10-14-1) and three methods of data sensitivity assessment for neural networks (Garson's algorithm, Olden's algorithm, Partial Derivatives method) combined with the simple ranking method, we evaluated the importance of 10 geomorphological indices correlated with earthquake magnitude. We find that group-1 is drainage density index (L) and Slope index (S) (average rank 28.5). Group-2 is the mountain front sinuosity index (Smf), drainage basin shape index (Bs) (average rank 18). The most important group-3 is asymmetry factor index (AF), focal statistics index (ΔGH) and hypsometric integral index (HI) (average rank 13.4). The last group-4 with the lowest earthquake magnitude correlation value includes stream length‒gradient index (SL), valley floor width to height ratio (Vf), fractal dimension (FD) (average rank 10.7). Using an MLP neural network with one hidden layer (8-18-1) and eight input geomorphological indices (L, S, Smf, Bs, AF, ΔGH, HI, SL), the earthquake prediction within the Cao Bang and neighboring provinces becomes MOb‒Max = 6.0 and includes the following seven sources: Song (River) Nuoc Den, Song Quay Son, Quang Yen-Song Bang, Cao Bang-Tien Yen, Song Ta Chien, Ha Giang, and Na Hang areas. [ABSTRACT FROM AUTHOR]

We present the results of gas-geochemical surveys in the sea surface water layer, water column, and bottom sediments of the Tatar Strait (north of the Sea of Japan) in 2012, 2014, 2015, 2017, and 2018. The distribution of methane fluxes at the water-atmosphere interface is examined, and its relationship with the geologic structure of the Tatar Strait area is discussed. Methane emission has been revealed throughout most of the Tatar Strait area. The most intense methane fluxes at the water-atmosphere interface, up to 482 mol/(km2×day), are observed on the gas-bearing southwestern shelf and on the gas hydrate slope of Sakhalin Island. The high concentrations of methane in seawater and the high contents of methane, hydrogen, and helium in the shelf and slope bottom sediments are probably due to the seismotectonic activity in the region, the presence of gas hydrates, gas concentration zones, gas migration channels, and the regional deep structure. Application of the model for calculation of the flux and impurity transfer fields to the studied water area has shown high methane emission from the sea surface in areas of vertical gas migration from lithospheric sources. The contribution of hydrodynamic factors to the formation of such zones of high methane emission is less than that of geologic factors. The obtained data on methane flux at the water-atmosphere interface for a shallow sea gave a detailed insight into the main gas discharge zones in the southern Tatar Strait. [ABSTRACT FROM AUTHOR]